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Stars

Stars are balls of luminous plasma, held together by gravity. They can be seen twinkling overhead from our planet each night. They are enjoyable to look at, but also have been used as navigation tools for centuries.

22,397 Questions
Astronomy
Stars

All about stars?

Stars are gigantic spheres of nucleosynthesis. They start off as hydrogen mainly but gradually fill up with heavier elements as they synthesise them.

Stars form from nebulae, vast clouds of hydrogen. Pockets of gas in the nebulae ball into spheres by gravity. Through tunnelling (relies on the Uncertainty Priciple of quantum theory), hydrogen nuclei fuse to form helium nuclei and this reaction gives of heat. Millions upon millions of these reactions heat up the star. Hydrogen is converted in this way (nucleosynthetically) into helium and helium into carbon.

A star is a 'delicate balance'. The heat from the core pushes outwards and the mass of the star tries to push the outer layers of the star inwards in collapse. Paradoxically, the larger a star the shorter is the time until it exhausts its nuclear 'fuel'. The nucleosynthetic reactions stop at iron. Energy must be addedto produce elements heavier than iron.

The largest stars (much larger than the Sun) explode as supernovae. The supernova energy is enough for the synthesis of the heavier elements, from iron to uranium.

With no nucleosynthetic energy continuing to be generated, the core collapses. Stars can shrink into white dwarves (where collapse is halted by electron degeneracy) or neutron stars (where collapse is halted by neutron degeneracy), or black holes, where collapse cannot be halted if the mass of the post-supernova core is above a certain limit - the Chandrasekhar limit.

There are a couple of videos on youtube about size and scale in the Universe. They start with the Moon and then show larger and larger and larger objects, from the Sun to Sirius and Aldebaran and the largest star so far known VY Canis Majoris.

The Sun is a star 150 million km from Earth and has a diameter of 1 390 000 km. The nearest star to the Sun is Proxima Centauri and is 4.3 light years from Earth.

Stars can be different colours, depending on their temperatures. Cool stars (from 3500 degrees Celsius) are redder in colour. The hottest stars are blue stars (up to 50 000 degrees Celsius). The Sun is 6000 degrees Celsius on the surface and 15 000 000 degrees Celsius at the centre and is classified as a type G yellow dwarf star.

Stars are classified by their size and colour on the Herzsprung-Russell Diagram.

Stars (in their billions) form huge groups (galaxies) thousands of light years in diameter. Galaxies have several shapes (spiral, barred spiral, elliptical and irregular).

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Astronomy
Stars

Where is the Aldorande star?

Answer

"Aldorande" is the pronunciation of a star called Alderaan.

Alderaan is the disused term for the stars Procyon and Gomesia in the constellation of Canis Minor.

So, your answer is the Canis Minor constellation. Even though the name Alderaan is no longer used.

Alderaan is also a fictional planet in the Star Wars movies.

Answer

Alderaan is pronounced Aldorande in the Star Wars movies and is a fictional planet.

The star Alderaan is an old and disused term for the stars Procyon and Gomeisa in the constellation Canis Minor.

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Astronomy
Stars

How are stars made?

It takes millions of years for free floating diatomic molecules of hydrogen gas in space to congregate in sufficient quantity to produce a protostar (the first stage). The collapse of the gas usually requires some event, such as a collision between gaseous nebula which tend to be inelastic, or the shockwave from a supernova, or the wake of a black hole. Any of these events can nudge gravity to coalesce the gas into a "brown dwarf."

When a brown dwarf has gained enough mass to emit its own light and heat via gravitational collapse, it becomes known as a "protostar." Protostars require 100,000 to a few million years to gain sufficient mass, core heat and pressure, to commence nuclear fusion, even though they can appear as bright as a "true" star. The most common true star is known as a T-Tauri star.

Nuclear fusion occurs as protons of hydrogen combine with neutrons to form helium nuclei (alpha particles). This process takes place in the core of the star, where the temperature is in the millions of degrees and the pressure is extremely high. Nuclear ignition is the point at which one may say a star is "born," and the resulting solar wind slows or halts the infalling nebular gas. Any remaining gas the star pulls into itself would come primarily from what is known as a protoplanetary accretion disk, usually forming parallel to the star's rotational axis.

Helium comes from the word helios, meaning "sun." The helium nucleus is lighter than its constituent parts--the two protons and neutrons of which it is formed. This difference is known as the "mass defect," and is equivalent to the energy liberated in the fusion process. So in its gestational state a protostar shines via gravitational collapse, until the core pressure and temperature is great enough for nuclear fusion, at which point the star shines by the nuclear fusion reaction.

Larger stars are less common, but can form in less time, such as by the collision of numerous protostars.
they are created with hot gasses from the nebula or really hot or exploded stars I believe
A star is born when gas and clouds of dust is forced/pushed together and forms a beautiful star.
they are created with hot gasses from the nebula or really hot or exploded stars I believe
A star is born when gas and clouds of dust is forced/pushed together and forms a beautiful star.

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Stars
Geometry

How many sides does a star have?

A star does not have a fixed number of sides as a triangle or quadrilateral does. A star may have five points, six points, or ten points. The number of sides is twice the number of points, so a six-pointed star has 12 sides.

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Planetary Science
The Moon
Stars

What is the circle of light around the sun called?

The circle of light around the sun is called a Corona. The corona can usually only be seen during a total solar eclipse. When this happens it can be seen as an irregularly shaped glow surrounding the moon.

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Astronomy
Stars

What are facts about a high mass star?

Mainly, a high mass star has a very short lifetime, because it uses its fuel in a much more wasteful manner: due to its higher mass, it will get much hotter, and the fusion will occur much faster.

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Astronomy
Stars
Neutron Stars

How does a super giant become a neutron star?

a massive star becomes red super giant which later results in a supernova explosion. after processes it either becomes a black hole or neutron star

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Astronomy
Seasons
Stars

Why does the Sun change position in the sky over different seasons?

The seasons are due to the motion of the Earth around the Sun. So, it may not be surprising that the Sun's position in the sky changes over seasons, due to the motion of the Earth around the Sun. The explanation is simple. All stars in the sky are moving, but the distant stars are so far away that we cannot detect appreciable motion (even when the Earth moves around the Sun). As a result, the positions of distant stars in the sky are fixed. At any single moment the Sun can be projected as a dot onto the night sky by extending the line that connects the Earth and the Sun (the line of sight) all the way to the sky. As the Earth orbits around the sun the line of sight changes direction and since the distant stars are fixed in the sky, the position of the Sun with respect to the distant stars changes.

<<>>

The main factor that changes the Sun's position in the sky is that the earth's axis of rotation is tilted. This means that the sun is higher above the horizon in the summer months than in the winter.

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Astronomy
Planetary Science
Stars

What angular resolution would you need to see the Sun and Jupiter as distinct points of light if you were looking at it from 15 light years away?

Great question to chew on ! And I think I can work it out, at least

to an order-of-magnitude approximation.

Radius of Jupiter's orbit is around 5 AU = 5 x 93 million = 465,000,000 miles.

15 light years = 15 x 5.8787 x 1012 = 8.818 x 1013 miles

(Tangent)-1 of (5 AU / 15 LY) = 0.000302 degree = roughly like 1.09 arc-second.

There's a rule for the resolution you need in order to completely resolve two sources

that subtend a given angle, and I don,t remember what it is. But the order of magnitude

for this particular case is about 1 arc-second ... with one bright object and a dim one.

That calculation looks right and the separation can theoretically be resolved by a telescope with a 4½" aperture. But there is a big difference in brightness because the Sun would be a star of magnitude 3.2 while Jupiter's magnitude would be about 21. So a considerably bigger telescope would be needed because to see something that dim needs a big aperture, round about 100".

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Astronomy
Stars

What is the biggest star seen from earth other than the sun?

The brightest star seen from Earth, aside from the Sun, is Sirius A. The Sun, of course, is nowhere near the largest star we can see. It only appears big to us because it is so much closer than any other star. Comment: That's not the answer to the question, of course. Even in big telescopes, all stars seem just like points of light from Earth. Perhaps the questioner meant the star we believe is the biggest, of those we can see.

Update: (Comment: This doesn't really answer the question, either.)

The top 10 brightest/biggest stars seen from Earth (minus the sun):

1 - Sirius (1.7 times the diameter of our sun, 9 light years away)

2 - Canopus (65 times solar diameter, 310 light years)

3 - Alpha Centauri

4 - Arcturus (26 times solar diameter, 37 light years)

5 - Vega (2.7 times solar diameter, 25 light years)

6 - Capella (12 times solar diameter, 43 light years away)

7 - Rigel (78 times solar diameter, 800 light years)

8 - Procyon (2 times solar radius, 11 light years)

9 - Achernar

10 - Betelgeuse (Alpha Orionis, 1180 times the diameter of our sun)

Comment. This is one possible answer to the question: VY Canis Majoris (2000 times solar diameter, 5000 light years away - not visible to naked eye). However estimates or the diameters of stars is difficult and there are other candidates for the "biggest star".

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Stars

Why do celestial bodies appear to move from east to west across the sky?

Stars, planets, moons, and various other bodies in space are collectively called celestial bodies. The stars, like the sun, appear to move from east to west. This apparent movement is due to Earth's rotation on its axis. However, there is one star that appears almost stationary to us. This is the Pole star, named so because it is in the direction of the North Pole. All the stars appear to rotate about a point very close to the Pole star, which appears to be almost stationary. The angle of the Pole star above the horizon gives us our latitude on Earth.

There are several other things going on at the same time:

  • The earth revolves about the sun once per year. As it does so, it's inner half faces the sun and sees daylight. Its outer half is in darkness. As it swings around the sun, this dark side points in different directions during the year. In the summer, the dark side points toward the center of the galaxy and the constellation Sagittarius. In the winter, the dark side points away from the center of the galaxy toward the constellation Orion. This is why you see different constellations during different times of the year.
  • Finally, the moon and planets have their own independent orbits which results in their paths being a bit different than the background stars. The moon is the easiest to explain, because it just moves around the earth once per month in a direction that makes it appear to go opposite its apparent rising and setting. The planets are a bit more complex, but their locations can be found using any astronomy chart.
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Astronomy
Physics
Stars

If time stands still at the speed of light why does it take 8 minutes for light from the sun to reach the earth?

According to relativity theory: from an observer's viewpoint it takes about 8 minutes. From the light's viewpoint it takes no time at all. (That's pushing the theory to the limit of course.)There's a lot of detailed stuff below, but that's basically the answer. Very Basic Answer:Because the time dilation explained by relativity affects the object (or light) traveling at relativistic speeds, and NOT observers watching the object (or light) go by. A Little More Information:Here is the reason this is so difficult to grasp. Time is NOT a universal constant. In our everyday experience of the world, it is clear that when a full day goes by for me, a full day will go by for you, no matter where you are on earth, and no matter what the clock time is that we each use to start measuring the day. We have an intuitive sense that time itself passes for me just as it passes for you or anyone anywhere in the world, and this would also be basically true for anyone living on a colony on any of our solar system's planets. It might take hours for a radio message to go from earth to the colony, but we understand that the passage and experience of time for the other party is the same as ours.

It makes perfect sense that we would believe that time is universally constant, because we do not have relativistic experiences that tell us otherwise, and because to us time seems to be so regular and so easily and consistently measured. But here is the big secret: Time is not a universal constant. It does not pass the same way for all locations and for all reference frames no matter what. Einstein theorized this and it has been supported many times in many ways. But you have to be dealing with relativistic velocities (velocities that are significant proportions of the speed of light) in order for the differences in time to be noticeable.

Now, we cannot accelerate to the speed of light. But if we are accelerating relative to our starting point, the closer we get to the speed of light the greater the relativistic affect on time. Light itself is NOT instantaneous; as far as we know from classical physics nothing propagates through space instantaneously. Maybe Quantum Theory allows for such things. Light takes 8 minutes to reach earth from the sun if the time is measured from earth. If you could hitch a ride on one of the photons coming from the sun, (you cannot, of course) first you would get a big shock when the photon hits the sand at your favorite beach. If you survive, YOU would claim that the trip was instantaneous. For YOU (not for observers on earth) time would NOT have passed during the trip from the sun. Yes, it seems impossible. But this is one of the consequences of Einstein's theories of relativity. There is another example of the time distortion idea involving black holes in the discussion area.

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Stars
Galaxies
Nuclear Physics

What causes the sun to produce light?

Heat from nuclear fusion produces massive amounts of energy. Thermal energy is usually associated with Light. The concept of heat creating light is the same basis as to why light bulbs get hot when you turn them on, or why metal gets bright red when you heat it up.

299300301
Astronomy
Stars

Which is the biggest star in night sky?

"Antares" is probably the largest star visible with the naked eye.

However, the largest star may be "VY Canis Majoris" which is about twice as big as Antares, but is not visible with the naked eye. Estimating the radius of a star is not easy and there are a few other possible answers as to what the biggest star actually is.

See related questions.

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Astronomy
Planetary Science
Stars

If the distance to a star is doubled its apparent intensity would what?

It would quarter.

If the distance to a star is doubled, its apparent intensity or brightness would be reduced to one quarter (1/4) that of its original intensity.

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Planetary Science
Stars
Galaxies

What do you call people who study planets and stars?

Astronomers.

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Astronomy
Planetary Science
Stars

Visual magnitude star is 7.3 tells you that?

That object is easily visible with a pair of binoculars.

A star's apparent brightness is exactly 100 times less than another star if its apparent magnitude is +5 greater. So, the star of magnitude 7.3 appears 100 times fainter than a star of magnitude 2.3. (Polaris is a bit brighter than magnitude 2.3).

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Planetary Science
Stars

What ordinarily keeps a star from collapsing?

Thermonuclear fusion reactions produce an outward pressure that counteracts the inward pressure that would lead to collapse due to gravity.

True, but not only! Equilibrium of gravitating bodies (stars, planets, nebula...) depends on state equation: pressure as a function of mass density, temperature. Radiative pressure is important for hot normal star sclasses, but not for dense neutron stars or dwarfs... Particularly, there is not radiation pressure in planets, which are keeping by the balance of gas/liquid pressure and gravitation...

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Astronomy
Planetary Science
Stars

What star is 70 light years away?

There are many, many stars that are at approximately that distance.

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Astronomy
Stars

Why the sun does not shine at night?

Sure it shines. We simply don't see it when it is below the horizon.

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Stars
Black Holes
Astrophysics
Betelgeuse

Is Betelgeuse a black hole?

No, it is a red supergiant star.

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Planetary Science
Stars

Is the north star a satellite or a planet?

Neither. It is actually a star. Its true name is Polaris, just as the true name of the sun is Sol. It is nicknamed the North Star because it is the only star that appears not to move in the sky, because its position is directly over the North Pole.

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Stars

How far out does the sun's gravity reach?

In physical terms - to the ends of the Universe.

In practical terms - to the edge, where something more massive has a greater influence.

In "our" terms, about 2 light years from the Sun (But all depends in which direction you are looking (thinking).

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Astronomy
Stars
Betelgeuse

What is Betelgeuse light distance from earth?

Its between 500 to 790 light years away, but it has been proven difficult to measure. 644 light years is the approximation.

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