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What is Stereopsis?

Updated: 9/15/2023
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Nettapper

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it refers to the ability to infer info on the 3D structure and distance of a scene from 2 or more images taken from different viewpoints

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What are the disadvantages of the parallax method?

Visual perceptionMain articles: stereopsis, depth perception, binocular vision, and Binocular disparityThis image demonstrates parallax. TheSun is visible above the streetlight. The reflection in the water is a virtual image of the Sun and the streetlight. The location of the virtual image is below the surface of the water, offering a different vantage point of the streetlight, which appears to be shifted relative to the more distant Sun.As the eyes of humans and other animals are in different positions on the head, they present different views simultaneously. This is the basis of stereopsis, the process by which the brain exploits the parallax due to the different views from the eye to gain depth perception and estimate distances to objects.[3] Animals also use motion parallax, in which the animals (or just the head) move to gain different viewpoints. For example, pigeons (whose eyes do not have overlapping fields of view and thus cannot use stereopsis) bob their heads up and down to see depth.[4]Parallax in astronomyParallax is an angle subtended by a line on a point. In the upper diagram the earth in its orbit sweeps the parallax angle subtended on the sun. The lower diagram shows an equal angle swept by the sun in a geostatic model. A similar diagram can be drawn for a star except that the angle of parallax would be tiny.Parallax arises due to change in viewpoint but that can occur due to motion of the observer, or of that which is being observed, or of both. What is essential is relative motion. By observing parallax, measuring angles and using geometry, one can determine the distance to various objects.Stellar parallaxMain article: Stellar parallaxStellar parallax created by the relative motion between the Earth and a star, can be seen, in the Copernican model, as arising from the orbit of the Earth around the Sun: the star onlyappears to move relative to more distant objects in the sky. In a geostatic model, the movement of the star would have to be taken as real with the star oscillating across the sky with respect to the background stars.Stellar parallax is most often measured using annual parallax, defined as the difference in position of a star as seen from the Earth and Sun, i. e. the angle subtended at a star by the mean radius of the Earth's orbit around the Sun. The parsec (3.26 light-years) is defined as the distance for which the annual parallax is 1 arcsecond. Annual parallax is normally measured by observing the position of a star at different times of the year as the Earth moves through its orbit. Measurement of annual parallax was the first reliable way to determine the distances to the closest stars. The first successful measurements of stellar parallax were made by Friedrich Bessel in 1838 for the star 61 Cygni using a heliometer.[5]Stellar parallax remains the standard for calibrating other measurement methods. Accurate calculations of distance based on stellar parallax require a measurement of the distance from the Earth to the Sun, now based on radar reflection off the surfaces of planets.[6]The angles involved in these calculations are very small and thus difficult to measure. The nearest star to the Sun (and thus the star with the largest parallax), Proxima Centauri, has a parallax of 0.7687 ± 0.0003 arcsec.[7] This angle is approximately that subtended by an object 2 centimeters in diameter located 5.3 kilometers away.The fact that stellar parallax was so small that it was unobservable at the time was used as the main scientific argument against heliocentrism during the early modern age. It is clear from Euclid's geometry that the effect would be undetectable if the stars were far enough away, but for various reasons such gigantic distances involved seemed entirely implausible: it was one of Tycho's principal objections to Copernican heliocentrism that in order for it to be compatible with the lack of observable stellar parallax, there would have to be an enormous and unlikely void between the orbit of Saturn and the eighth sphere (the fixed stars).[8]In 1989, the satellite Hipparcos was launched primarily for obtaining parallaxes and proper motions of nearby stars, increasing the reach of the method tenfold. Even so, Hipparcos is only able to measure parallax angles for stars up to about 1,600 light-years away, a little more than one percent of the diameter of the Milky Way Galaxy. The European Space Agency's Gaia mission, due to launch in August 2013, will be able to measure parallax angles to an accuracy of 10 microarcseconds, thus mapping nearby stars (and potentially planets) up to a distance of tens of thousands of light-years from earth.[9]ComputationStellar parallax motionDistance measurement by parallax is a special case of the principle of triangulation, which states that one can solve for all the sides and angles in a network of triangles if, in addition to all the angles in the network, the length of at least one side has been measured. Thus, the careful measurement of the length of one baseline can fix the scale of an entire triangulation network. In parallax, the triangle is extremely long and narrow, and by measuring both its shortest side (the motion of the observer) and the small top angle (always less than 1 arcsecond,[5] leaving the other two close to 90 degrees), the length of the long sides (in practice considered to be equal) can be determined.Assuming the angle is small (see derivation below), the distance to an object (measured in parsecs) is the reciprocal of the parallax (measured in arcseconds): For example, the distance to Proxima Centauri is 1/0.7687=1.3009 parsecs (4.243 ly).[7]Diurnal parallaxDiurnal parallax is a parallax that varies with rotation of the Earth or with difference of location on the Earth. The Moon and to a smaller extent the terrestrial planets or asteroids seen from different viewing positions on the Earth (at one given moment) can appear differently placed against the background of fixed stars.[10][11] Lunar parallaxLunar parallax (often short for lunar horizontal parallax or lunar equatorial horizontal parallax), is a special case of (diurnal) parallax: the Moon, being the nearest celestial body, has by far the largest maximum parallax of any celestial body, it can exceed 1 degree.[12] The diagram (above) for stellar parallax can illustrate lunar parallax as well, if the diagram is taken to be scaled right down and slightly modified. Instead of 'near star', read 'Moon', and instead of taking the circle at the bottom of the diagram to represent the size of the Earth's orbit around the Sun, take it to be the size of the Earth's globe, and of a circle around the Earth's surface. Then, the lunar (horizontal) parallax amounts to the difference in angular position, relative to the background of distant stars, of the Moon as seen from two different viewing positions on the Earth:- one of the viewing positions is the place from which the Moon can be seen directly overhead at a given moment (that is, viewed along the vertical line in the diagram); and the other viewing position is a place from which the Moon can be seen on the horizon at the same moment (that is, viewed along one of the diagonal lines, from an Earth-surface position corresponding roughly to one of the blue dots on the modified diagram).The lunar (horizontal) parallax can alternatively be defined as the angle subtended at the distance of the Moon by the radius of the Earth[13] -- equal to angle p in the diagram when scaled-down and modified as mentioned above.The lunar horizontal parallax at any time depends on the linear distance of the Moon from the Earth. The Earth-Moon linear distance varies continuously as the Moon follows its perturbed and approximately elliptical orbit around the Earth. The range of the variation in linear distance is from about 56 to 63.7 earth-radii, corresponding to horizontal parallax of about a degree of arc, but ranging from about 61.4' to about 54'.[12] The Astronomical Almanac and similar publications tabulate the lunar horizontal parallax and/or the linear distance of the Moon from the Earth on a periodical e.g. daily basis for the convenience of astronomers (and formerly, of navigators), and the study of the way in which this coordinate varies with time forms part of lunar theory.Diagram of daily lunar parallaxParallax can also be used to determine the distance to the Moon.One way to determine the lunar parallax from one location is by using a lunar eclipse. A full shadow of the Earth on the Moon has an apparent radius of curvature equal to the difference between the apparent radii of the Earth and the Sun as seen from the Moon. This radius can be seen to be equal to 0.75 degree, from which (with the solar apparent radius 0.25 degree) we get an Earth apparent radius of 1 degree. This yields for the Earth-Moon distance 60.27 Earth radii or 384,399 kilometres (238,854 mi) This procedure was first used by Aristarchus of Samos[14] and Hipparchus, and later found its way into the work of Ptolemy.[citation needed] The diagram at right shows how daily lunar parallax arises on the geocentric and geostatic planetary model in which the Earth is at the centre of the planetary system and does not rotate. It also illustrates the important point that parallax need not be caused by any motion of the observer, contrary to some definitions of parallax that say it is, but may arise purely from motion of the observed.Another method is to take two pictures of the Moon at exactly the same time from two locations on Earth and compare the positions of the Moon relative to the stars. Using the orientation of the Earth, those two position measurements, and the distance between the two locations on the Earth, the distance to the Moon can be triangulated:Example of lunar parallax: Occultation of Pleiades by the MoonThis is the method referred to by Jules Verne in From the Earth to the Moon:Until then, many people had no idea how one could calculate the distance separating the Moon from the Earth. The circumstance was exploited to teach them that this distance was obtained by measuring the parallax of the Moon. If the word parallax appeared to amaze them, they were told that it was the angle subtended by two straight lines running from both ends of the Earth's radius to the Moon. If they had doubts on the perfection of this method, they were immediately shown that not only did this mean distance amount to a whole two hundred thirty-four thousand three hundred and forty-seven miles (94,330 leagues), but also that the astronomers were not in error by more than seventy miles (≈ 30 leagues).Solar parallaxAfter Copernicus proposed his heliocentric system, with the Earth in revolution around the Sun, it was possible to build a model of the whole solar system without scale. To ascertain the scale, it is necessary only to measure one distance within the solar system, e.g., the mean distance from the Earth to the Sun (now called an astronomical unit, or AU). When found by triangulation, this is referred to as the solar parallax, the difference in position of the Sun as seen from the Earth's centre and a point one Earth radius away, i. e., the angle subtended at the Sun by the Earth's mean radius. Knowing the solar parallax and the mean Earth radius allows one to calculate the AU, the first, small step on the long road of establishing the size and expansion age[15] of the visible Universe. A primitive way to determine the distance to the Sun in terms of the distance to the Moon was already proposed by Aristarchus of Samos in his book On the Sizes and Distances of the Sun and Moon. He noted that the Sun, Moon, and Earth form a right triangle (right angle at the Moon) at the moment of first or last quarter moon. He then estimated that the Moon, Earth, Sun angle was 87°. Using correct geometry but inaccurate observational data, Aristarchus concluded that the Sun was slightly less than 20 times farther away than the Moon. The true value of this angle is close to 89° 50', and the Sun is actually about 390 times farther away.[14] He pointed out that the Moon and Sun have nearly equal apparent angular sizes and therefore their diameters must be in proportion to their distances from Earth. He thus concluded that the Sun was around 20 times larger than the Moon; this conclusion, although incorrect, follows logically from his incorrect data. It does suggest that the Sun is clearly larger than the Earth, which could be taken to support the heliocentric model[citation needed].Measuring Venus transit times to determine solar parallaxAlthough Aristarchus' results were incorrect due to observational errors, they were based on correct geometric principles of parallax, and became the basis for estimates of the size of the solar system for almost 2000 years, until the transit of Venus was correctly observed in 1761 and 1769.[14] This method was proposed by Edmond Halley in 1716, although he did not live to see the results. The use of Venus transits was less successful than had been hoped due to the black drop effect, but the resulting estimate, 153 million kilometers, is just 2% above the currently accepted value, 149.6 million kilometers.Much later, the Solar System was 'scaled' using the parallax of asteroids, some of which, such as Eros, pass much closer to Earth than Venus. In a favourable opposition, Eros can approach the Earth to within 22 million kilometres.[16] Both the opposition of 1901 and that of 1930/1931 were used for this purpose, the calculations of the latter determination being completed by Astronomer Royal Sir Harold Spencer Jones.[17]Also radar reflections, both off Venus (1958) and off asteroids, like Icarus, have been used for solar parallax determination. Today, use of spacecraft telemetry links has solved this old problem. The currently accepted value of solar parallax is 8".794 143.[18]Dynamic or moving-cluster parallaxMain article: Moving cluster methodThe open stellar cluster Hyades in Taurus extends over such a large part of the sky, 20 degrees, that the proper motions as derived from astrometry appear to converge with some precision to a perspective point north of Orion. Combining the observed apparent (angular) proper motion in seconds of arc with the also observed true (absolute) receding motion as witnessed by the Doppler redshift of the stellar spectral lines, allows estimation of the distance to the cluster (151 light-years) and its member stars in much the same way as using annual parallax.[19]Dynamic parallax has sometimes also been used to determine the distance to a supernova, when the optical wave front of the outburst is seen to propagate through the surrounding dust clouds at an apparent angular velocity, while its true propagation velocity is known to be the speed of light.[20]DerivationFor a right triangle, where is the parallax, 1 AU (149,600,000 km) is approximately the average distance from the Sun to Earth, and is the distance to the star. Using small-angle approximations (valid when the angle is small compared to 1radian),so the parallax, measured in arcseconds, isIf the parallax is 1", then the distance isThis defines the parsec, a convenient unit for measuring distance using parallax. Therefore, the distance, measured in parsecs, is simply , when the parallax is given in arcseconds.[21]Parallax error in astronomyPrecise parallax measurements of distance have an associated error. However this error in the measured parallax angle does not translate directly into an error for the distance, except for relatively small angles. The reason for this is that an error toward a smaller angle results in a greater error in distance than an error toward a larger angle. However, an approximation of the distance error can be computed bywhere d is the distance and p is the parallax. The approximation is far more accurate for parallax errors that are small relative to the parallax than for relatively large errors. For meaningful results in stellar astronomy, Dutch astronomer Floor van Leeuwen recommends that the parallax error be no more than 10% of the total parallax when computing this error estimate.[22]Parallax error in measurement instrumentsThe correct line of sight needs to be used to avoid parallax error.Measurements made by viewing the position of some marker relative to something to be measured are subject to parallax error if the marker is some distance away from the object of measurement and not viewed from the correct position. For example, if measuring the distance between two ticks on a line with a ruler marked on its top surface, the thickness of the ruler will separate its markings from the ticks. If viewed from a position not exactly perpendicular to the ruler, the apparent position will shift and the reading will be less accurate than the ruler is capable of.A similar error occurs when reading the position of a pointer against a scale in an instrument such as an analog multimeter. To help the user avoid this problem, the scale is sometimes printed above a narrow strip of mirror, and the user's eye is positioned so that the pointer obscures its own reflection, guaranteeing that the user's line of sight is perpendicular to the mirror and therefore to the scale. The same effect alters the speed read on a car's speedometer by a driver in front of it and a passenger off to the side, values read from a graticule not in actual contact with the display on an oscilloscope, etc.Photogrammetric parallaxAerial picture pairs, when viewed through a stereo viewer, offer a pronounced stereo effect of landscape and buildings. High buildings appear to 'keel over' in the direction away from the centre of the photograph. Measurements of this parallax are used to deduce the height of the buildings, provided that flying height and baseline distances are known. This is a key component to the process of photogrammetry. Parallax error in photographyContax III rangefinder camera with macro photography setting. Because the viewfinder is on top of the lens and of the close proximity of the subject, goggles are fitted in front of the rangefinder and a dedicated viewfinder installed to compensate for parallax.Parallax error can be seen when taking photos with many types of cameras, such as twin-lens reflex cameras and those including viewfinders (such as rangefinder cameras). In such cameras, the eye sees the subject through different optics (the viewfinder, or a second lens) than the one through which the photo is taken. As the viewfinder is often found above the lens of the camera, photos with parallax error are often slightly lower than intended, the classic example being the image of person with his or her head cropped off. This problem is addressed in single-lens reflex cameras, in which the viewfinder sees through the same lens through which the photo is taken (with the aid of a movable mirror), thus avoiding parallax error.Parallax is also an issue in image stitching, such as for panoramas.In computer graphicsMain articles: Parallax scrolling and Parallax mappingIn many early graphical applications, such as video games, the scene was constructed of independent layers that were scrolled at different speeds in a simulated parallax motion effect when the player/cursor moved, a method called parallax scrolling. Some hardware had explicit support for such layers, such as the Super Nintendo Entertainment System. This gave some layers the appearance of being farther away than others and was useful for creating an illusion of depth, but only worked when the player was moving. Now, most games are based on much more comprehensive three-dimensional graphic models, although portable game systems (such as Nintendo DS) still often use parallax.[citation needed]Parallax-based graphics continue to be used for many online applications where the bandwidth required by three-dimensional graphics is excessive.[citation needed]Parallax scrolling has also been adapted to website design generally implemented using javascript and modern web standards.[23] The technique has since appeared in many different forms and variations on virtually thousands of websites.Parallax in sightsParallax affects sights in many ways. On sights fitted to small arms, bows in archery, etc. the distance between the sighting mechanism and the weapon's bore or axis can introduce significant errors when firing at close range, particularly when firing at small targets. This difference is generally referred to as "sight height"[24] and is compensated for (when needed) via calculations that also take in other variables such as bullet drop, windage, and the distance at which the target is expected to be.[25] Sight height can be used to advantage when "sighting-in" rifles for field use. A typical hunting rifle (.222 with telescopic sights) sighted-in at 75m will be useful from 50m to 200m without further adjustment.[citation needed] Parallax in optical sightsFurther information: Telescopic sight#Parallax compensationIn optical sights parallax refers to the apparent movement of the reticle in relationship to the target when the user moves his/her head laterally behind the sight (up/down or left/right),[26] i.e. it is an error where the reticle does not stay aligned with the sight's own optical axis.In optical instruments such as telescopes, microscopes, or in telescopic sights used on small arms and theodolites, the error occurs when the optics are not precisely focused: the reticle will appear to move with respect to the object focused on if one moves one's head sideways in front of the eyepiece. Some firearm telescopic sights are equipped with a parallax compensation mechanism which basically consists of a movable optical element that enables the optical system to project the picture of objects at varying distances and the reticle crosshairs pictures together in exactly the same optical plane. Telescopic sights may have no parallax compensation because they can perform very acceptably without refinement for parallax with the sight being permanently adjusted for the distance that best suits their intended usage. Typical standard factory parallax adjustment distances for hunting telescopic sights are 100 yd or 100 m to make them suited for hunting shots that rarely exceed 300 yd/m. Some target and military style telescopic sights without parallax compensation may be adjusted to be parallax free at ranges up to 300 yd/m to make them better suited for aiming at longer ranges.[citation needed] Scopes for rimfires, shotguns, and muzzleloaders will have shorter parallax settings, commonly 50 yd/m[citation needed] for rimfire scopes and 100 yd/m[citation needed] for shotguns and muzzleloaders. Scopes for airguns are very often found with adjustable parallax, usually in the form of an adjustable objective, or AO. These may adjust down as far as 3 yards (2.74 m).[citation needed]Non-magnifying reflector or "reflex" sights have the ability to be theoretically "parallax free". But since these sights use parallel collimated light this is only true when the target is at infinity. At finite distances eye movement perpendicular to the device will cause parallax movement in the reticle image in exact relationship to eye position in the cylindrical column of light created by the collimating optics.[27][28] Firearm sights, such as some red dot sights, try to correct for this via not focusing the reticle at infinity, but instead at some finite distance, a designed target range where the reticle will show very little movement due to parallax.[27] Some manufactures market reflector sight models they call "parallax free",[29] but this refers to an optical system that compensates for off axis spherical aberration, an optical error induced by the spherical mirror used in the sight that can cause the reticle position to diverge off the sight's optical axis with change in eye position.[30][31]Artillery gunfireBecause of the positioning of field or naval artillery guns, each one has a slightly different perspective of the target relative to the location of the fire-control system itself. Therefore, when aiming its guns at the target, the fire control system must compensate for parallax in order to assure that fire from each gun converges on the target. Parallax rangefindersParallax theory for finding naval distancesA coincidence rangefinder or parallax rangefinder can be used to find distance to a target.As a metaphorIn a philosophic/geometric sense: An apparent change in the direction of an object, caused by a change in observational position that provides a new line of sight. The apparent displacement, or difference of position, of an object, as seen from two different stations, or points of view. In contemporary writing parallax can also be the same story, or a similar story from approximately the same time line, from one book told from a different perspective in another book. The word and concept feature prominently in James Joyce's 1922 novel, Ulysses. Orson Scott Card also used the term when referring to Ender's Shadow as compared to Ender's Game. The artist Sarah Morris named her studio Parallax, in reference to her parallel production of paintings and films. The metaphor is invoked by Slovenian philosopher Slavoj Žižek in his work The Parallax View. Žižek borrowed the concept of "parallax view" from the Japanese philosopher and literary critic Kojin Karatani. "The philosophical twist to be added (to parallax), of course, is that the observed distance is not simply subjective, since the same object that exists 'out there' is seen from two different stances, or points of view. It is rather that, as Hegel would have put it, subject and object are inherently mediated so that an 'epistemological' shift in the subject's point of view always reflects an ontological shift in the object itself. Or-to put it in Lacanese-the subject's gaze is always-already inscribed into the perceived object itself, in the guise of its 'blind spot,' that which is 'in the object more than object itself', the point from which the object itself returns the gaze. Sure the picture is in my eye, but I am also in the picture

Related questions

What are the grades of binocular vision?

Simultaneous macular perception,fusion and stereopsis

What is the prefix of opsis?

the prefix means 'sight' in the sense of stereopsis seeing solid objects

What is 3D LED Display?

3D Displays is a device capable of conveying depth perception to the viewer by means of stereopsis for binocular vision.3 D display technology that enables a three-dimensional effect, so that viewers perceive that an image has depth as well as height and width, similarly to objects in the real world.

What does modal eye mean?

Infants first become sensitive at about two months to kinematic, or motion-carried information for distance, as when one surface moves in front of another. At about four months, infants are able to perceive depth via the difference in the optical projections at the two retinas to determine depth, known as stereopsis.

What is phoria?

To maintain stereopsis and singleness of vision, the eye need to be pointed accurately.The position of each eye in its orbit is controlled by six extraocular muscles. Slight differences in the length or insertion position or strength of the same muscle in the two eyes can lead to a tendency for one eye to drift position in its orbit from the other, especially when one is tired. This is known as Phoria.

What is the function of optic chiasm in the body?

the optic chiasm is the cross-shape when some of the information from the left eye and right eye cross over and pass into opposite sides of the brain. stereopsis is a binocular depth cue, the greater the difference between the view seen by the left and right eye the closer the viewer is looking. since the image seen by both eyes is different it uses the optic chiasm to pass into both sides of the brain so it can be interpreted by the visual cortex.

How do you use synoptophore?

It is a piece of equipment used by orthoptists who specialize in dealing with eye squints and binocular single vision. The synoptophore can help to measure the angle of the squint present i.e how big it is and you can measure the angle in different position of gazes. it cam also be use to measure vertical and torsional deviations. Motor and sensory fusion can also be measure along with stereopsis (3D) vision . First the patient's IPD is set by keeping your head straight and aligning the patient's eyes with the white line on the eyepieces. To measure the angle of deviation the tubes are moved in towards you if it is an inward deviation and move the tube away from you to measure a outward deviation in degrees. For sensory and motor fusion the tubes are converged and then diverged until the patient cant see the image as single .

What factors are needed for binocular vision?

Most people find this concept of binocular vision confusing. The word binocular conjures up an image of the hand-held, dual-eyepiece telescope that is used for birdwatching and at sports competitions to see the action up close. Binocular vision, however, refers to a particular perspective or way of seeing the world.In binocular vision, the eyes are used together to produce a view that is stereoscopic or three dimensional (3-D). This means that we can see things in terms of their length, width, and depth. We share this feature with other animals, such as monkeys, hawks, cats and dogs.Our eyes are located forward in the head and some distance apart, with the nose serving as a divider in between. This attribute enables us to obtain two distinct views of the same object, each seen from a slightly different angle or parallax. Our brain combines these images to create a stereoscopic, three-dimensional reference in our visual field.Binocular vision has three primary advantages over monocular vision, or vision in which only one eye is used.A wider horizontal visual field (one eye = 150°; two eyes = 180°+)It gives binocular summation or an enhanced ability to detect faint imagesIt gives stereopsis or precise depth perception.what factors are responsible for binocular vision

How does 3D television work?

A TV showing 3D content displays two separate images of the same scene simultaneously, one intended for the viewer's right eye and one for the left eye. The two full-size images occupy the entire screen and appear intermixed with one another - objects in one image are often repeated or skewed slightly to the left (or right) of corresponding objects in the other - when viewed without the aid of special 3D glasses. When viewers don the glasses, they perceive these two images as a single 3D image, a process known as "fusing."The system relies on a phenomenon of visual perception called stereopsis. The eyes of an adult human lie about 2.5 inches apart, which lets each eye see objects from slightly different angles. The two images on a 3D TV screen present objects from two slightly different angles as well, and when those images combine in the viewer's mind with the aid of the glasses, the illusion of depth is created.It's the same as the 3d you experience on movie theaters. The light comes out as a polarized one. One polaroid in your glasses lets pass 1 type of light while the other part is passed by the other one. So you get two perspective of the same image which is kind of like real life. In real life your eyes see the same object in different perspective which then your brain merges to make a 3D picture.The other method is the glasses(electronic ones) lets one image display at one eye and then after a fraction of a second the same image is displayed in the other eye. So your brain is forced to perceive the two images as the same image even though they are displayed after a certain delay.

What are the disadvantages of the parallax method?

Visual perceptionMain articles: stereopsis, depth perception, binocular vision, and Binocular disparityThis image demonstrates parallax. TheSun is visible above the streetlight. The reflection in the water is a virtual image of the Sun and the streetlight. The location of the virtual image is below the surface of the water, offering a different vantage point of the streetlight, which appears to be shifted relative to the more distant Sun.As the eyes of humans and other animals are in different positions on the head, they present different views simultaneously. This is the basis of stereopsis, the process by which the brain exploits the parallax due to the different views from the eye to gain depth perception and estimate distances to objects.[3] Animals also use motion parallax, in which the animals (or just the head) move to gain different viewpoints. For example, pigeons (whose eyes do not have overlapping fields of view and thus cannot use stereopsis) bob their heads up and down to see depth.[4]Parallax in astronomyParallax is an angle subtended by a line on a point. In the upper diagram the earth in its orbit sweeps the parallax angle subtended on the sun. The lower diagram shows an equal angle swept by the sun in a geostatic model. A similar diagram can be drawn for a star except that the angle of parallax would be tiny.Parallax arises due to change in viewpoint but that can occur due to motion of the observer, or of that which is being observed, or of both. What is essential is relative motion. By observing parallax, measuring angles and using geometry, one can determine the distance to various objects.Stellar parallaxMain article: Stellar parallaxStellar parallax created by the relative motion between the Earth and a star, can be seen, in the Copernican model, as arising from the orbit of the Earth around the Sun: the star onlyappears to move relative to more distant objects in the sky. In a geostatic model, the movement of the star would have to be taken as real with the star oscillating across the sky with respect to the background stars.Stellar parallax is most often measured using annual parallax, defined as the difference in position of a star as seen from the Earth and Sun, i. e. the angle subtended at a star by the mean radius of the Earth's orbit around the Sun. The parsec (3.26 light-years) is defined as the distance for which the annual parallax is 1 arcsecond. Annual parallax is normally measured by observing the position of a star at different times of the year as the Earth moves through its orbit. Measurement of annual parallax was the first reliable way to determine the distances to the closest stars. The first successful measurements of stellar parallax were made by Friedrich Bessel in 1838 for the star 61 Cygni using a heliometer.[5]Stellar parallax remains the standard for calibrating other measurement methods. Accurate calculations of distance based on stellar parallax require a measurement of the distance from the Earth to the Sun, now based on radar reflection off the surfaces of planets.[6]The angles involved in these calculations are very small and thus difficult to measure. The nearest star to the Sun (and thus the star with the largest parallax), Proxima Centauri, has a parallax of 0.7687 ± 0.0003 arcsec.[7] This angle is approximately that subtended by an object 2 centimeters in diameter located 5.3 kilometers away.The fact that stellar parallax was so small that it was unobservable at the time was used as the main scientific argument against heliocentrism during the early modern age. It is clear from Euclid's geometry that the effect would be undetectable if the stars were far enough away, but for various reasons such gigantic distances involved seemed entirely implausible: it was one of Tycho's principal objections to Copernican heliocentrism that in order for it to be compatible with the lack of observable stellar parallax, there would have to be an enormous and unlikely void between the orbit of Saturn and the eighth sphere (the fixed stars).[8]In 1989, the satellite Hipparcos was launched primarily for obtaining parallaxes and proper motions of nearby stars, increasing the reach of the method tenfold. Even so, Hipparcos is only able to measure parallax angles for stars up to about 1,600 light-years away, a little more than one percent of the diameter of the Milky Way Galaxy. The European Space Agency's Gaia mission, due to launch in August 2013, will be able to measure parallax angles to an accuracy of 10 microarcseconds, thus mapping nearby stars (and potentially planets) up to a distance of tens of thousands of light-years from earth.[9]ComputationStellar parallax motionDistance measurement by parallax is a special case of the principle of triangulation, which states that one can solve for all the sides and angles in a network of triangles if, in addition to all the angles in the network, the length of at least one side has been measured. Thus, the careful measurement of the length of one baseline can fix the scale of an entire triangulation network. In parallax, the triangle is extremely long and narrow, and by measuring both its shortest side (the motion of the observer) and the small top angle (always less than 1 arcsecond,[5] leaving the other two close to 90 degrees), the length of the long sides (in practice considered to be equal) can be determined.Assuming the angle is small (see derivation below), the distance to an object (measured in parsecs) is the reciprocal of the parallax (measured in arcseconds): For example, the distance to Proxima Centauri is 1/0.7687=1.3009 parsecs (4.243 ly).[7]Diurnal parallaxDiurnal parallax is a parallax that varies with rotation of the Earth or with difference of location on the Earth. The Moon and to a smaller extent the terrestrial planets or asteroids seen from different viewing positions on the Earth (at one given moment) can appear differently placed against the background of fixed stars.[10][11] Lunar parallaxLunar parallax (often short for lunar horizontal parallax or lunar equatorial horizontal parallax), is a special case of (diurnal) parallax: the Moon, being the nearest celestial body, has by far the largest maximum parallax of any celestial body, it can exceed 1 degree.[12] The diagram (above) for stellar parallax can illustrate lunar parallax as well, if the diagram is taken to be scaled right down and slightly modified. Instead of 'near star', read 'Moon', and instead of taking the circle at the bottom of the diagram to represent the size of the Earth's orbit around the Sun, take it to be the size of the Earth's globe, and of a circle around the Earth's surface. Then, the lunar (horizontal) parallax amounts to the difference in angular position, relative to the background of distant stars, of the Moon as seen from two different viewing positions on the Earth:- one of the viewing positions is the place from which the Moon can be seen directly overhead at a given moment (that is, viewed along the vertical line in the diagram); and the other viewing position is a place from which the Moon can be seen on the horizon at the same moment (that is, viewed along one of the diagonal lines, from an Earth-surface position corresponding roughly to one of the blue dots on the modified diagram).The lunar (horizontal) parallax can alternatively be defined as the angle subtended at the distance of the Moon by the radius of the Earth[13] -- equal to angle p in the diagram when scaled-down and modified as mentioned above.The lunar horizontal parallax at any time depends on the linear distance of the Moon from the Earth. The Earth-Moon linear distance varies continuously as the Moon follows its perturbed and approximately elliptical orbit around the Earth. The range of the variation in linear distance is from about 56 to 63.7 earth-radii, corresponding to horizontal parallax of about a degree of arc, but ranging from about 61.4' to about 54'.[12] The Astronomical Almanac and similar publications tabulate the lunar horizontal parallax and/or the linear distance of the Moon from the Earth on a periodical e.g. daily basis for the convenience of astronomers (and formerly, of navigators), and the study of the way in which this coordinate varies with time forms part of lunar theory.Diagram of daily lunar parallaxParallax can also be used to determine the distance to the Moon.One way to determine the lunar parallax from one location is by using a lunar eclipse. A full shadow of the Earth on the Moon has an apparent radius of curvature equal to the difference between the apparent radii of the Earth and the Sun as seen from the Moon. This radius can be seen to be equal to 0.75 degree, from which (with the solar apparent radius 0.25 degree) we get an Earth apparent radius of 1 degree. This yields for the Earth-Moon distance 60.27 Earth radii or 384,399 kilometres (238,854 mi) This procedure was first used by Aristarchus of Samos[14] and Hipparchus, and later found its way into the work of Ptolemy.[citation needed] The diagram at right shows how daily lunar parallax arises on the geocentric and geostatic planetary model in which the Earth is at the centre of the planetary system and does not rotate. It also illustrates the important point that parallax need not be caused by any motion of the observer, contrary to some definitions of parallax that say it is, but may arise purely from motion of the observed.Another method is to take two pictures of the Moon at exactly the same time from two locations on Earth and compare the positions of the Moon relative to the stars. Using the orientation of the Earth, those two position measurements, and the distance between the two locations on the Earth, the distance to the Moon can be triangulated:Example of lunar parallax: Occultation of Pleiades by the MoonThis is the method referred to by Jules Verne in From the Earth to the Moon:Until then, many people had no idea how one could calculate the distance separating the Moon from the Earth. The circumstance was exploited to teach them that this distance was obtained by measuring the parallax of the Moon. If the word parallax appeared to amaze them, they were told that it was the angle subtended by two straight lines running from both ends of the Earth's radius to the Moon. If they had doubts on the perfection of this method, they were immediately shown that not only did this mean distance amount to a whole two hundred thirty-four thousand three hundred and forty-seven miles (94,330 leagues), but also that the astronomers were not in error by more than seventy miles (≈ 30 leagues).Solar parallaxAfter Copernicus proposed his heliocentric system, with the Earth in revolution around the Sun, it was possible to build a model of the whole solar system without scale. To ascertain the scale, it is necessary only to measure one distance within the solar system, e.g., the mean distance from the Earth to the Sun (now called an astronomical unit, or AU). When found by triangulation, this is referred to as the solar parallax, the difference in position of the Sun as seen from the Earth's centre and a point one Earth radius away, i. e., the angle subtended at the Sun by the Earth's mean radius. Knowing the solar parallax and the mean Earth radius allows one to calculate the AU, the first, small step on the long road of establishing the size and expansion age[15] of the visible Universe. A primitive way to determine the distance to the Sun in terms of the distance to the Moon was already proposed by Aristarchus of Samos in his book On the Sizes and Distances of the Sun and Moon. He noted that the Sun, Moon, and Earth form a right triangle (right angle at the Moon) at the moment of first or last quarter moon. He then estimated that the Moon, Earth, Sun angle was 87°. Using correct geometry but inaccurate observational data, Aristarchus concluded that the Sun was slightly less than 20 times farther away than the Moon. The true value of this angle is close to 89° 50', and the Sun is actually about 390 times farther away.[14] He pointed out that the Moon and Sun have nearly equal apparent angular sizes and therefore their diameters must be in proportion to their distances from Earth. He thus concluded that the Sun was around 20 times larger than the Moon; this conclusion, although incorrect, follows logically from his incorrect data. It does suggest that the Sun is clearly larger than the Earth, which could be taken to support the heliocentric model[citation needed].Measuring Venus transit times to determine solar parallaxAlthough Aristarchus' results were incorrect due to observational errors, they were based on correct geometric principles of parallax, and became the basis for estimates of the size of the solar system for almost 2000 years, until the transit of Venus was correctly observed in 1761 and 1769.[14] This method was proposed by Edmond Halley in 1716, although he did not live to see the results. The use of Venus transits was less successful than had been hoped due to the black drop effect, but the resulting estimate, 153 million kilometers, is just 2% above the currently accepted value, 149.6 million kilometers.Much later, the Solar System was 'scaled' using the parallax of asteroids, some of which, such as Eros, pass much closer to Earth than Venus. In a favourable opposition, Eros can approach the Earth to within 22 million kilometres.[16] Both the opposition of 1901 and that of 1930/1931 were used for this purpose, the calculations of the latter determination being completed by Astronomer Royal Sir Harold Spencer Jones.[17]Also radar reflections, both off Venus (1958) and off asteroids, like Icarus, have been used for solar parallax determination. Today, use of spacecraft telemetry links has solved this old problem. The currently accepted value of solar parallax is 8".794 143.[18]Dynamic or moving-cluster parallaxMain article: Moving cluster methodThe open stellar cluster Hyades in Taurus extends over such a large part of the sky, 20 degrees, that the proper motions as derived from astrometry appear to converge with some precision to a perspective point north of Orion. Combining the observed apparent (angular) proper motion in seconds of arc with the also observed true (absolute) receding motion as witnessed by the Doppler redshift of the stellar spectral lines, allows estimation of the distance to the cluster (151 light-years) and its member stars in much the same way as using annual parallax.[19]Dynamic parallax has sometimes also been used to determine the distance to a supernova, when the optical wave front of the outburst is seen to propagate through the surrounding dust clouds at an apparent angular velocity, while its true propagation velocity is known to be the speed of light.[20]DerivationFor a right triangle, where is the parallax, 1 AU (149,600,000 km) is approximately the average distance from the Sun to Earth, and is the distance to the star. Using small-angle approximations (valid when the angle is small compared to 1radian),so the parallax, measured in arcseconds, isIf the parallax is 1", then the distance isThis defines the parsec, a convenient unit for measuring distance using parallax. Therefore, the distance, measured in parsecs, is simply , when the parallax is given in arcseconds.[21]Parallax error in astronomyPrecise parallax measurements of distance have an associated error. However this error in the measured parallax angle does not translate directly into an error for the distance, except for relatively small angles. The reason for this is that an error toward a smaller angle results in a greater error in distance than an error toward a larger angle. However, an approximation of the distance error can be computed bywhere d is the distance and p is the parallax. The approximation is far more accurate for parallax errors that are small relative to the parallax than for relatively large errors. For meaningful results in stellar astronomy, Dutch astronomer Floor van Leeuwen recommends that the parallax error be no more than 10% of the total parallax when computing this error estimate.[22]Parallax error in measurement instrumentsThe correct line of sight needs to be used to avoid parallax error.Measurements made by viewing the position of some marker relative to something to be measured are subject to parallax error if the marker is some distance away from the object of measurement and not viewed from the correct position. For example, if measuring the distance between two ticks on a line with a ruler marked on its top surface, the thickness of the ruler will separate its markings from the ticks. If viewed from a position not exactly perpendicular to the ruler, the apparent position will shift and the reading will be less accurate than the ruler is capable of.A similar error occurs when reading the position of a pointer against a scale in an instrument such as an analog multimeter. To help the user avoid this problem, the scale is sometimes printed above a narrow strip of mirror, and the user's eye is positioned so that the pointer obscures its own reflection, guaranteeing that the user's line of sight is perpendicular to the mirror and therefore to the scale. The same effect alters the speed read on a car's speedometer by a driver in front of it and a passenger off to the side, values read from a graticule not in actual contact with the display on an oscilloscope, etc.Photogrammetric parallaxAerial picture pairs, when viewed through a stereo viewer, offer a pronounced stereo effect of landscape and buildings. High buildings appear to 'keel over' in the direction away from the centre of the photograph. Measurements of this parallax are used to deduce the height of the buildings, provided that flying height and baseline distances are known. This is a key component to the process of photogrammetry. Parallax error in photographyContax III rangefinder camera with macro photography setting. Because the viewfinder is on top of the lens and of the close proximity of the subject, goggles are fitted in front of the rangefinder and a dedicated viewfinder installed to compensate for parallax.Parallax error can be seen when taking photos with many types of cameras, such as twin-lens reflex cameras and those including viewfinders (such as rangefinder cameras). In such cameras, the eye sees the subject through different optics (the viewfinder, or a second lens) than the one through which the photo is taken. As the viewfinder is often found above the lens of the camera, photos with parallax error are often slightly lower than intended, the classic example being the image of person with his or her head cropped off. This problem is addressed in single-lens reflex cameras, in which the viewfinder sees through the same lens through which the photo is taken (with the aid of a movable mirror), thus avoiding parallax error.Parallax is also an issue in image stitching, such as for panoramas.In computer graphicsMain articles: Parallax scrolling and Parallax mappingIn many early graphical applications, such as video games, the scene was constructed of independent layers that were scrolled at different speeds in a simulated parallax motion effect when the player/cursor moved, a method called parallax scrolling. Some hardware had explicit support for such layers, such as the Super Nintendo Entertainment System. This gave some layers the appearance of being farther away than others and was useful for creating an illusion of depth, but only worked when the player was moving. Now, most games are based on much more comprehensive three-dimensional graphic models, although portable game systems (such as Nintendo DS) still often use parallax.[citation needed]Parallax-based graphics continue to be used for many online applications where the bandwidth required by three-dimensional graphics is excessive.[citation needed]Parallax scrolling has also been adapted to website design generally implemented using javascript and modern web standards.[23] The technique has since appeared in many different forms and variations on virtually thousands of websites.Parallax in sightsParallax affects sights in many ways. On sights fitted to small arms, bows in archery, etc. the distance between the sighting mechanism and the weapon's bore or axis can introduce significant errors when firing at close range, particularly when firing at small targets. This difference is generally referred to as "sight height"[24] and is compensated for (when needed) via calculations that also take in other variables such as bullet drop, windage, and the distance at which the target is expected to be.[25] Sight height can be used to advantage when "sighting-in" rifles for field use. A typical hunting rifle (.222 with telescopic sights) sighted-in at 75m will be useful from 50m to 200m without further adjustment.[citation needed] Parallax in optical sightsFurther information: Telescopic sight#Parallax compensationIn optical sights parallax refers to the apparent movement of the reticle in relationship to the target when the user moves his/her head laterally behind the sight (up/down or left/right),[26] i.e. it is an error where the reticle does not stay aligned with the sight's own optical axis.In optical instruments such as telescopes, microscopes, or in telescopic sights used on small arms and theodolites, the error occurs when the optics are not precisely focused: the reticle will appear to move with respect to the object focused on if one moves one's head sideways in front of the eyepiece. Some firearm telescopic sights are equipped with a parallax compensation mechanism which basically consists of a movable optical element that enables the optical system to project the picture of objects at varying distances and the reticle crosshairs pictures together in exactly the same optical plane. Telescopic sights may have no parallax compensation because they can perform very acceptably without refinement for parallax with the sight being permanently adjusted for the distance that best suits their intended usage. Typical standard factory parallax adjustment distances for hunting telescopic sights are 100 yd or 100 m to make them suited for hunting shots that rarely exceed 300 yd/m. Some target and military style telescopic sights without parallax compensation may be adjusted to be parallax free at ranges up to 300 yd/m to make them better suited for aiming at longer ranges.[citation needed] Scopes for rimfires, shotguns, and muzzleloaders will have shorter parallax settings, commonly 50 yd/m[citation needed] for rimfire scopes and 100 yd/m[citation needed] for shotguns and muzzleloaders. Scopes for airguns are very often found with adjustable parallax, usually in the form of an adjustable objective, or AO. These may adjust down as far as 3 yards (2.74 m).[citation needed]Non-magnifying reflector or "reflex" sights have the ability to be theoretically "parallax free". But since these sights use parallel collimated light this is only true when the target is at infinity. At finite distances eye movement perpendicular to the device will cause parallax movement in the reticle image in exact relationship to eye position in the cylindrical column of light created by the collimating optics.[27][28] Firearm sights, such as some red dot sights, try to correct for this via not focusing the reticle at infinity, but instead at some finite distance, a designed target range where the reticle will show very little movement due to parallax.[27] Some manufactures market reflector sight models they call "parallax free",[29] but this refers to an optical system that compensates for off axis spherical aberration, an optical error induced by the spherical mirror used in the sight that can cause the reticle position to diverge off the sight's optical axis with change in eye position.[30][31]Artillery gunfireBecause of the positioning of field or naval artillery guns, each one has a slightly different perspective of the target relative to the location of the fire-control system itself. Therefore, when aiming its guns at the target, the fire control system must compensate for parallax in order to assure that fire from each gun converges on the target. Parallax rangefindersParallax theory for finding naval distancesA coincidence rangefinder or parallax rangefinder can be used to find distance to a target.As a metaphorIn a philosophic/geometric sense: An apparent change in the direction of an object, caused by a change in observational position that provides a new line of sight. The apparent displacement, or difference of position, of an object, as seen from two different stations, or points of view. In contemporary writing parallax can also be the same story, or a similar story from approximately the same time line, from one book told from a different perspective in another book. The word and concept feature prominently in James Joyce's 1922 novel, Ulysses. Orson Scott Card also used the term when referring to Ender's Shadow as compared to Ender's Game. The artist Sarah Morris named her studio Parallax, in reference to her parallel production of paintings and films. The metaphor is invoked by Slovenian philosopher Slavoj Žižek in his work The Parallax View. Žižek borrowed the concept of "parallax view" from the Japanese philosopher and literary critic Kojin Karatani. "The philosophical twist to be added (to parallax), of course, is that the observed distance is not simply subjective, since the same object that exists 'out there' is seen from two different stances, or points of view. It is rather that, as Hegel would have put it, subject and object are inherently mediated so that an 'epistemological' shift in the subject's point of view always reflects an ontological shift in the object itself. Or-to put it in Lacanese-the subject's gaze is always-already inscribed into the perceived object itself, in the guise of its 'blind spot,' that which is 'in the object more than object itself', the point from which the object itself returns the gaze. Sure the picture is in my eye, but I am also in the picture

Standard ophthalmic exam?

DefinitionA standard ophthalmic exam is a series of tests done to check your vision and the health of your eyes.See also: Refraction testAlternative NamesRoutine eye examination; Eye exam - standard; Snellen chartHow the test is performedThe eye doctor will ask questions about your overall health and family's medical history. You should tell the doctor if you have noticed any eye problems.The doctor checks your vision (visual acuity) using a chart of random letters of different sizes. This is called the Snellen chart.To see inside your eye, the doctor looks through a magnifying glass that has a light on the end (an ophthalmoscope). The device allows the doctor to see the retina and nearby blood vessels, back of the eye (fundus), and optic nerve area.Sometimes, you'll be given eye drops so that the doctor can better view the back of the eye. Another magnifying device called a slit lamp is used to see the clear surface of the eye (cornea). See: Slit-lamp examDifferent machines and methods test your eye's reaction to light, eye movement, and side (peripheral) vision. To see if you need glasses, the doctor places several lenses in front of your eye, one at a time, and asks you when the letters on the Snellen chart are easier to see.Color blindnessis tested using multicolored dots that form numbers. See: Color vision testThe doctor checks for glaucoma using a method called tonometry.How to prepare for the testMake an appointment with an eye doctor (some take walk-in patients). Avoid eye strain the day of the test. You may need someone to drive you home if the doctor uses eye drops to perform certain eye tests.How the test will feelThe tests cause no pain or discomfort.Why the test is performedYou should have regular eye exams. Such exams allow for early detection of eye problems and help determine the cause of vision changes.Various eye and medical problems can be found by a routine eye test, including glaucoma, cataracts, high blood pressure, macular degeneration, and diabetes. People with diabetes should have their eyes examined at least once a year.Certain types of work require that you get eye exams. For example, pilots, race car drivers, and military personnel.Normal Values20/20 (normal) visionAbility to differentiate colorsNo signs of glaucomaNormal optic nerve, retinal vessels, and fundusWhat abnormal results meanAbnormal results may be due to:Age-related macular degeneration (ARMD)AstigmatismBlocked tear ductCataractsColor blindnessCorneal abrasion (or dystrophy)Corneal ulcers and infectionsDamaged nerves or blood vessels in the eyeDiabetes-related nerve damage in the eye (diabetic retinopathy)GlaucomaHyperopiaLazy eye(amblyopia)MyopiaPresbyopiaStrabismusTraumaThis list may not be all-inclusiveWhat the risks areIf you received drops to dilate your eyes for the ophthalmoscopy, your vision will be blurred and sunlight can damage your eye. Wear dark glasses or shade your eyes to avoid discomfort until the dilation wears off.Special considerationsMany eye diseases, if detected early, are curable or can be treated.

What are a few words that have ere in it?

abampere abamperes accoutered adhere adhered adherence adherences adherend adherends adherent adherently adherents adherer adherers adheres administered adulterer adulterers adulteress adulteresses aerenchyma aerenchymas aerenchymata afferent afferently afferents aftereffect aftereffects altered alterer alterers ampere amperes angered answered answerer answerers antimere antimeres antlered anywhere anywheres aphaereses aphaeresis aphaeretic aphereses apheresis ashlered asthenosphere asthenospheres atmosphere atmosphered atmospheres attempered austere austerely austereness austerenesses austerer austerest backscattered bacteremia bacteremias bacteremic badgered banistered bannered banneret bannerets bannerette bannerettes bantered banterer banterers barbered bartered barterer barterers bathysphere bathyspheres battered bayadere bayaderes beavered bediapered befingered beflowered beleaguered belligerence belligerences belligerencies belligerency belligerent belligerently belligerents belvedere belvederes bereave bereaved bereavement bereavements bereaver bereavers bereaves bereaving bereft beret berets beretta berettas bergere bergeres beshivered bespattered betattered bettered bewhiskered bewildered bewilderedly bewilderedness bewilderednesses bickered bickerer bickerers bioengineered biosphere biospheres bistered bittered bitterer bitterest blabbered blastomere blastomeres blathered blatherer blatherers blattered blethered blinkered blistered blithered blubbered blundered blunderer blunderers blustered blusterer blusterers bolstered bolsterer bolsterers bordereau bordereaux bordered borderer borderers bothered bouldered boutonniere boutonnieres bowered brassiere brassieres broidered brokered brothered buccaneered bucklered buckminsterfullerene buckminsterfullerenes buffered buggered bumpered bunkered butchered buttered butterfingered calendered calenderer calenderers calipered callipered cambered cankered cantered cantilevered capered caperer caperers carabiniere 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counterefforts counterespionage counterespionages counterevidence counterevidences counterexample counterexamples counterordered countertransference countertransferences couturiere couturieres covered coverer coverers cowered craniocerebral cratered cumbered cumberer cumberers cylindered cyphered cytodifferentiation cytodifferentiations dackered daggered daikered dandered dangered dapperer dapperest daundered decentered decerebrate decerebrated decerebrates decerebrating decerebration decerebrations deciphered decipherer decipherers dedifferentiate dedifferentiated dedifferentiates dedifferentiating dedifferentiation dedifferentiations deference deferences deferent deferential deferentially deferents deflowered deflowerer deflowerers delivered deliverer deliverers delustered demergered dere derealization derealizations deregulate deregulated deregulates deregulating deregulation deregulations derelict dereliction derelictions derelicts derepress derepressed derepresses derepressing 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etherealnesses everywhere exosphere exospheres faltered falterer falterers farmerette farmerettes fathered feathered featheredge featheredged featheredges featheredging fellmongered fendered fere feres feretories feretory festered fettered fetterer fetterers fevered fibered filibustered filibusterer filibusterers filtered filterer filterers fingered fingerer fingerers flattered flatterer flatterers fleered flichtered flickered flittered floundered flowered flowerer flowerers floweret flowerets flowerette flowerettes flustered flusteredly fluttered flutterer flutterers foddered foregathered forereach forereached forereaches forereaching forgathered fostered fosterer fosterers foundered fourragere fourrageres frere freres frittered fritterer fritterers fruiterer fruiterers fullered fullerene fullerenes funereal funereally furthered furtherer furtherers galere galeres gandered garnered gartered gathered gatherer gatherers gauffered gendered gerent gerents gerenuk gerenuks gerrymandered gettered gibbered gibberellin gibberellins gingered glandered glasspapered glimmered glistered glittered glowered godfathered goffered gomerel gomerels grandfathered gruyere gruyeres guttered haeredes haeres haltere haltered halteres hammered hammerer hammerers hampered hamperer hamperers hankered hankerer hankerers harbingered havered haverel haverels headquartered helicoptered hemisphere hemispheres here hereabout hereabouts hereafter hereafters hereat hereaway hereaways hereby heredes hereditament hereditaments hereditarian hereditarians hereditarily hereditary heredities heredity herein hereinabove hereinafter hereinbefore hereinbelow hereinto hereof hereon heres heresiarch heresiarchs heresies heresy heretic heretical heretically heretics hereto heretofore heretrices heretrix heretrixes hereunder hereunto hereupon herewith hexerei hexereis hindered hinderer hinderers hollered holstered homered hovered hoverer hoverers huckstered hungered hunkered hydrosere hydroseres hydrosphere hydrospheres hyperefficient hyperemia hyperemias hyperemic hyperemotional hyperemotionalities hyperemotionality hyperendemic hyperenergetic hyperesthesia hyperesthesias hyperesthetic hypereutectic hypereutectoid hyperexcitabilities hyperexcitability hyperexcitable hyperexcited hyperexcitement hyperexcitements hyperexcretion hyperexcretions hyperextend hyperextended hyperextending hyperextends hyperextension hyperextensions hysterectomies hysterectomized hysterectomy hystereses hysteresis hysteretic imbittered imbowered impowered incoherence incoherences incoherent incoherently incumbered indifference indifferences indifferencies indifferency indifferent indifferentism indifferentisms indifferentist indifferentists indifferently inference inferences inferential inferentially ingathered inhere inhered inherence inherences inherent inherently inheres insincere insincerely insphere insphered inspheres interelectrode interelectrodes interelectron interelectronic interepidemic interest interested interestedly interesting interestingly interestingness interestingnesses interests interethnic interfere interfered interference interferences interferential interferer interferers interferes interlayered intracerebral intracerebrally ionosphere ionospheres irreverence irreverences irreverent irreverently isoproterenol isoproterenols isothere isotheres jabbered jabberer jabberers jackhammered jardiniere jardinieres jeered jeerer jeerers jereed jereeds jeremiad jeremiads jiggered jittered juddered kashered kedgeree kedgerees kerseymere kerseymeres kippered kipperer kipperers knackered koshered laagered lackered lacquered lacquerer lacquerers laddered lagered lanneret lannerets lappered lathered latherer latherers laundered launderer launderers launderette launderettes lavaliere lavalieres lavalliere lavallieres laveered lavendered lawyered layered leaguered leathered leatherette leatherettes lechered leered leistered lettered letterer letterers levered leveret leverets lightered limbered limberer limberest lingered lingerer lingerers lippered lithosphere lithospheres littered litterer litterers lobstered loitered loiterer loiterers loppered louvered lowered lumbered lumberer lumberers lustered mackerel mackerels macromere macromeres magnetosphere magnetospheres makereadies makeready maladministered malingered malingerer malingerers mammered manageress manageresses maneuvered maneuverer maneuverers mannered mastered mattered maundered maunderer maunderers meandered membered mere merely merengue merengues merer meres merest meretricious meretriciously meretriciousness meretriciousnesses mesomere mesomeres mesosphere mesospheres metamere metameres metered meuniere mezereon mezereons mezereum mezereums microampere microamperes micromere micromeres microsphere microspheres milliampere milliamperes minaudiere minaudieres ministered misaltered misentered miserere misereres misnomered misordered misreference misreferences misregistered misremembered misrendered missteered mitered miterer miterers moldered mongered mothered mouldered mufflered multichambered multilayered multitiered multitowered murdered murderee murderees murderer murderers murderess murderesses murthered mustered mutineered muttered mutterer mutterers nattered nereid nereides nereids nereis nereises neutered newspapered nickered niffered nonbelligerencies nonbelligerency nonbelligerent nonbelligerents noncoherent nonconference nonconferences nonhereditary noninterest noninterests noninterference noninterferences nonpreferential noosphere noospheres nowhere nowheres numbered numberer numberers ochered offered offerer offerers officered oosphere oospheres operetta operettas operettist operettists ordered orderer orderers otherwhere outcapered outdelivered outglittered outhomered outmaneuvered outnumbered outpowered outsteered outtowered overdifferentiation overdifferentiations overeager overeagerness overeagernesses overearnest overeasy overeat overeaten overeater overeaters overeating overeats overed overedit overedited overediting overedits overeducate overeducated overeducates overeducating overeducation overeducations overelaborate overelaborated overelaborates overelaborating overelaboration overelaborations overembellish overembellished overembellishes overembellishing overembellishment overembellishments overemote overemoted overemotes overemoting overemotional overemphases overemphasis overemphasize overemphasized overemphasizes overemphasizing overemphatic overenamored overencourage overencouraged overencourages overencouraging overenergetic overengineer overengineered overengineering overengineers overenrolled overentertained overenthusiasm overenthusiasms overenthusiastic overenthusiastically overequipped overestimate overestimated overestimates overestimating overestimation overestimations overevaluation overevaluations overexaggerate overexaggerated overexaggerates overexaggerating overexaggeration overexaggerations overexcite overexcited overexcites overexciting overexercise overexercised overexercises overexercising overexert overexerted overexerting overexertion overexertions overexerts overexpand overexpanded overexpanding overexpands overexpansion overexpansions overexpectation overexpectations overexplain overexplained overexplaining overexplains overexplicit overexploit overexploitation overexploitations overexploited overexploiting overexploits overexpose overexposed overexposes overexposing overexposure overexposures overextend overextended overextending overextends overextension overextensions overextraction overextractions overextrapolation overextrapolations overextravagant overexuberant overmannered overmastered overpowered overwatered overwintered oystered oysterer oysterers ozonosphere ozonospheres palavered paltered palterer palterers pampered pamperer pamperers pamphleteered pandered panderer panderers papered paperer paperers partnered pattered patterer patterers paupered peered peeress peeresses peltered peppered pepperer pepperers perea peregrin peregrinate peregrinated peregrinates peregrinating peregrination peregrinations peregrine peregrines peregrins pereia pereion pereiopod pereiopods peremptorily peremptoriness peremptorinesses peremptory perennate perennated perennates perennating perennation perennations perennial perennially perennials pereon pereopod pereopods perestroika perestroikas persevere persevered perseveres pestered pesterer pesterers petered pewterer pewterers philandered philanderer philanderers philtered photosphere photospheres pickeered pickerel pickerels pickerelweed pickerelweeds pilfered pilferer pilferers pioneered plaistered planisphere planispheres plasmaphereses plasmapheresis plastered plasterer plasterers plateresque plundered plunderer plunderers podomere podomeres pondered ponderer ponderers portered portiere portieres pothered pottered potterer potterers poulterer poulterers powdered powderer powderers powered preerect preerected preerecting preerects preference preferences preferential preferentially premiere premiered premieres prenumbered preordered prerecession prerecord prerecorded prerecording prerecords preregister preregistered preregistering preregisters preregistration preregistrations prerehearsal prerelease prereleases prerenal prerequire prerequired prerequires prerequiring prerequisite prerequisites preretirement preretirements prereturn prereview prerevisionist prerevisionists prerevolution prerevolutionary prisere priseres privateered proffered profiteered properer properest prospered puckered puckerer puckerers puttered putterer putterers quaere quaeres quartered quavered quaverer quaverers queered queerer queerest quivered quiverer quiverers racketeered raftered rapiered realtered rechartered reconnoitered reconquered reconsidered recovered recoverer recoverers redelivered rediscovered reembroidered reencountered reengineered reentered reerect reerected reerecting reerects referee refereed refereeing referees reference referenced references referencing referenda referendum referendums referent referential referentialities referentiality referentially referents refiltered reflowered regathered registered rehammered rejiggered relacquered relettered remaindered remastered remembered rememberer rememberers rencountered rendered renderer renderers renumbered reoffered reordered repapered replastered repowered reread rereading rereadings rereads rerecord rerecorded rerecording rerecords reredos reredoses reregister reregistered reregistering reregisters reregistration reregistrations reregulate reregulated reregulates reregulating reregulation reregulations rerelease rereleased rereleases rereleasing reremice reremind rereminded rereminding rereminds reremouse rerepeat rerepeated rerepeating rerepeats rereview rereviewed rereviewing rereviews rereward rerewards resilvered resoldered retempered reupholstered reuttered revere revered reverence reverenced reverencer reverencers reverences reverencing reverend reverends reverent reverential reverentially reverently reverer reverers reveres rhabdomere rhabdomeres rhizosphere rhizospheres riviere rivieres roistered roisterer roisterers roystered rubbered sabered saggered sandpapered sarcomere sarcomeres sauntered saunterer saunterers scampered scarpered scattered scatterer scatterers sceptered schliere schlieren schmeered schwarmerei schwarmereis sclereid sclereids sclerenchyma sclerenchymas sclerenchymata sclerenchymatous scouthered scowdered scunnered scuppered scuttered seeress seeresses semierect sepulchered sequestered sere sered serein sereins serenade serenaded serenader serenaders serenades serenading serenata serenatas serenate serendipities serendipitous serendipitously serendipity serene serenely sereneness serenenesses serener serenes serenest serenities serenity serer seres serest severe severed severely severeness severenesses severer severest sewered shattered sheered sheerer sheerest sheltered shelterer shelterers shereef shereefs shimmered shivered shiverer shiverers shouldered showered showerer showerers shuddered shuttered sidereal silvered silverer silverers simmered simpered simperer simperers sincere sincerely sincereness sincerenesses sincerer sincerest sintered sistered skeltered skewered skippered skittered slabbered slandered slanderer slanderers slathered slaughtered slaughterer slaughterers slavered slaverer slaverers sledgehammered slenderer slenderest slippered slithered slivered sliverer sliverers slobbered slobberer slobberers sloganeered slubbered slumbered slumberer slumberers smattered smatterer smatterers smithereens smoldered smothered smouldered sneakered sneered sneerer sneerers snickered snickerer snickerers sniggered sniggerer sniggerers snookered sobered soberer soberest soldered solderer solderers soldiered soleret solerets solleret sollerets somewhere somewheres sorcerer sorcerers sorceress sorceresses sovereign sovereignly sovereigns sovereignties sovereignty spattered speered sphere sphered spheres spiered spinneret spinnerets spinnerette spinnerettes splattered splintered spluttered splutterer splutterers sprinklered sputtered sputterer sputterers squandered squanderer squanderers squattered staggered staggerer staggerers stammered stammerer stammerers steamered steamrollered steered steerer steerers stere stereo stereochemical stereochemistries stereochemistry stereoed stereogram stereograms stereograph stereographed stereographic stereographies stereographing stereographs stereography stereoing stereoisomer stereoisomeric stereoisomerism stereoisomerisms stereoisomers stereological stereologically stereologies stereology stereomicroscope stereomicroscopes stereomicroscopic stereomicroscopically stereophonic stereophonically stereophonies stereophony stereophotographic stereophotographies stereophotography stereopses stereopsides stereopsis stereopticon stereopticons stereoregular stereoregularities stereoregularity stereos stereoscope stereoscopes stereoscopic stereoscopically stereoscopies stereoscopy stereospecific stereospecifically stereospecificities stereospecificity stereotactic stereotaxic stereotaxically stereotype stereotyped stereotyper stereotypers stereotypes stereotypic stereotypical stereotypically stereotypies stereotyping stereotypy steres stoppered strangered stratosphere stratospheres stuttered stutterer stutterers suberect subsere subseres suckered suffered sufferer sufferers summered sundered sunderer sunderers supercalendered supered supereffective superefficiencies superefficiency superefficient superego superegoist superegoists superegos superelevate superelevated superelevates superelevating superelevation superelevations superelite superelites supereminence supereminences supereminent supereminently superencipher superenciphered superenciphering superenciphers supererogation supererogations supererogatory superette superettes superexpensive superexpress superexpresses superpowered surrendered suspendered swaggered swaggerer swaggerers sweltered swimmeret swimmerets swithered synaereses synaeresis synereses syneresis syphered tabered tafferel tafferels tampered tamperer tamperers tapered taperer taperers tattered teetered teleconference teleconferenced teleconferences teleconferencing teleconferencings telemetered telfered telomere telomeres telphered tempered temperer temperers tendered tenderer tenderers tenderest tentered terebene terebenes terebic terebinth terebinths teredines teredo teredos terefah terephthalate terephthalates terete tethered there thereabout thereabouts thereafter thereat thereby therefor therefore therefrom therein thereinafter thereinto theremin theremins thereof thereon theres thereto theretofore thereunder thereunto thereupon therewith therewithal thermosphere thermospheres thundered thunderer thunderers tiered tigereye tigereyes tillered timbered tinkered tinkerer tinkerers tittered titterer titterers tochered torchere torcheres tottered totterer totterers towered trailered transferee transferees transference transferences transferential transgendered tricornered triggered troposphere tropospheres trouvere trouveres tuckered turnverein turnvereins tutoyered tuyere tuyeres twittered ulcered umbered unaltered unanswered unbarbered unbelligerent unbuffered unbuttered unceremonious unceremoniously unceremoniousness unceremoniousnesses unchartered uncluttered unconquered unconsidered uncovered undeciphered undelivered undereat undereaten undereating undereats undereducated underemphases underemphasis underemphasize underemphasized underemphasizes underemphasizing underemployed underemployment underemployments underestimate underestimated underestimates underestimating underestimation underestimations underexpose underexposed underexposes underexposing underexposure underexposures underpowered understeered undifferentiated undiscovered unembittered unencumbered unfathered unfettered unfiltered unhampered unhindered uninterest uninterested uninteresting uninterests unlaundered unlettered unlimbered unmannered unmanneredly unmitered unnumbered unordered unpuckered unrecovered unregistered unremembered unsoldered unsphere unsphered unspheres unstoppered untempered untethered unweathered upgathered upholstered upholsterer upholsterers ushered usherette usherettes uttered utterer utterers veered velveret velverets veneered veneerer veneerers venereal verderer verderers verecund vicegerencies vicegerency vicegerent vicegerents viceregal viceregally vicereine vicereines videoconference videoconferences videoconferencing videoconferencings vivandiere vivandieres volunteered vouchered wafered wagered wagerer wagerers wallpapered wandered wanderer wanderers watered waterer waterers wavered waverer waverers weathered weltered were weregild weregilds werewolf werewolves westered where whereabout whereabouts whereas whereases whereat whereby wherefore wherefores wherefrom wherein whereinto whereof whereon wheres wheresoever wherethrough whereto whereunto whereupon wherever wherewith wherewithal wherewithals whickered whimpered whiskered whispered whisperer whisperers wildered wintered winterer winterers withered witherer witherers wondered wonderer wonderers woolgatherer woolgatherers wuthered xerosere xeroseres yabbered yammered yammerer yammerers yattered zippered

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