Sunlight interacting with the Earth's atmosphere makes the sky blue. In outer space the astronauts see blackness because outer space has no atmosphere.

Sunlight consists of light waves of varying wavelengths, each of which is seen as a different color. The minute particles of matter and molecules of air in the atmosphere intercept and scatter the white light of the sun. A larger portion of the blue color in white light is scattered, more so than any other color because the blue wavelengths are the shortest.

When the size of atmospheric particles are smaller than the wavelengths of the colors, selective scattering occurs-the particles only scatter one color and the atmosphere will appear to be that color. Blue wavelengths especially are affected, bouncing off the air particles to become visible.

This is why the sun looks yellow from Earth (yellow equals white minus blue). In space, the sun appears white because there is nothing in between to scatter its white light.

At sunset, the sky changes color because as the sun drops to the horizon, sunlight has more atmosphere to pass through and loses more of its blue wavelengths. The orange and red, having the longer wavelengths and making up more of sunlight at this distance, are most likely to be scattered by the air particles.

The scattering of visible light by atmospheric gases is most correctly called the Tyndall effect, but it is more commonly known to physicists as Rayleigh scattering after Lord Rayleigh, who studied it in more detail a few years later. Rayleigh Scattering is where red, orange, yellow, and green are passed through and blue, indigo, and violet are "scattered" out creating the color.

Whichever direction you look, some of this scattered blue light reaches you. Since you see the blue light from everywhere overhead, the sky looks blue.

(*As for why the sky does not appear violet -- the wavelength most scattered -- see the explanation at the related link below.)

Blue light is scattered in all directions by the tiny molecules of air in Earth's atmosphere. Blue is scattered more than other colors because it travels as shorter, smaller waves. This is why we see a blue sky most of the time.
The sky appears blue to us because of the scattering of the blue light component of the light from the Sun. Some alpine lakes also appear a quite light blue colour for the same reason, light is scattered by tiny suspended flakes of minerals in the water.
Because the water particles in the air split the light and Blue light is dispersed the furthest that's why it creates the illusion the sky is blue

The world's highest recorded air temperature is officially recognized by the World Meteorological Organization as 134°F (57.6°C) recorded at Death Valley, California, USA on 10 July 1913.

Note that this is in recorded history. Higher temperatures have occurred, of course, at different times during the 4.55 billion years of Earth's history.

Related Information:

El Azizia, Libya, held this record for 90 years, after recording a temperature of 136°F (58°C) on 13 September 1922. It was coincidentally also on 13 September of 2012 that this record was stripped by the World Meteorological Organization after a team of experts determined that there were enough questions surrounding this measurement that this temperature probably did not occur.

The temperature had been suspect in atmospheric science circles for a number of reasons. One being that the time of year is inconsistent with such a high reading. Also, the type and exposure of the measuring instruments cast doubt on the accuracy of the data. However, other temperatures in the same general area approach that maximum, especially in the cloudless southern Sahara, far from the moderating effects of water. Several links are provided below for more information on this process.

Other Earth Temperature Highs:

The modern, most reliably recorded air temperature in the world was 129.2°F (54.0°C) at Death Valley on 30 June 2013.

The highest naturally occurring temperature (at Earth's core) is higher than the melting point of iron and is estimated to be approximately 5000°C.

The highest temperature ever created in a laboratory experiment: Scientists, using the Z machine, have produced plasma at temperatures of more than 2 billion degrees Kelvin (3.6 billion degrees F) at Sandia National Laboratories, located near Albuquerque New Mexico.

Dasht-e Lut, a desert in southeastern Iran, was identified as having the hottest surface temperature (not air temperature) of 70.7 degrees C (159 degrees F) This was only during the years of study in 2004 and 2005 by MODIS, which is a satellite remote sensor, mounted on NASA satellites Aqua and Terra.

Caveats to the Above:

Modern measuring methods, instruments, and techniques are more sophisticated and standardized today. Example: The World Meteorological Organization, recommends that air temperatures be measured at a height of 1.25 to 2 meters (which is approximately 4 feet, 1.2 inches to 6 feet, 6.7 inches) above ground level.

The most likely places on Earth for record high temperatures are in depressions in desert regions, especially in areas below sea level. The Dallol (Danakil) Depression in Africa (Ethiopia), Death Valley in USA, and the area around Lake Eyre in Australia are likely candidates. However, the Gobi Desert's temperatures, while far from any ocean, are mitigated by altitude. The Dallol Depression had a weather station for a short while (only a few years). It was run by a mining company, and wasn't there long enough to measure an extreme maximum to beat the Libyan record. It did however, measure very high mean average temperatures while it operated.

The thing to remember about very hot places is that data is sparse. This is because very few people with high levels of technology stay in these places for long. The environment of the Dallol Depression is hostile to human life. 135

134.6

The instrument, most commonly used in science, is a barometer.

Related Information:

The word, Barometer, is derived from baro, meaning weight or pressure, and meter, meaning measuring device.

Barometers can be either analog or digital. The traditional analog barometer is known as an aneroid barometer. These are the round chrome or brass type that you would normally see on the bridge of a ship, many times accompanied by clock, temperature, and/or humidity gauge.

For an accurate and reliable aneroid barometer, you should expect to pay $249.00 or more. For aneroid barometers, accuracy and reliability will wane incrementally below that price. The cost of scientific instruments, including barometers, are directly tied to accuracy and reliability. In some cases, however, as you go up in price, accuracy will remain stable but quality of materials and craftsmanship will drive the price upwards (i.e. use of thick solid brass or chrome).

Digital barometers emulate the results achieved from an aneroid barometer (sometimes called a "nautical barometer). Their accuracy varies wildly and is not necessarily tied to price. For example, the barometers, in even the most reasonably priced (under $100.00) La Crosse Weather Stations, are exemplary performers. Anecdotal observations over many years show that the La Crosse variance from NIST traceable, accurate weather stations has been minimal (±.01). Other inexpensive manufacturer's products have nowhere near this steady and predictable tolerance. And many are as much as .06-.10 or 2-3mb off after initial calibration.

All barometers are not the same. Most have elevation limitations. With the Weems & Plath barometers, specific elevations are designated by each individual product. So, be sure to probe for this information before you buy. Some barometers can be upgraded for high elevation use. But this is relatively expensive, and generally for those barometers to be used in terrain of 5,000ft.

Digital barometers can have the same limitations. Again, be careful when you purchase. We are not aware of any low cost digital that will function correctly over 5,000-6,000 ft elevation. For high altitudes, or if you're a stickler for accuracy, you must consider the Davis, RainWise, WeatherHawk, or Columbia Weather Systems. Do not rely on any barometer above 5,000-6,000 ft for mission critical or safety applications, unless you are absolutely certain of its well defined and guaranteed specifications. Remember that as you begin to challenge the stated limitations of any scientific device, your inaccuracies will almost certainly increase as you approach the stated threshold. For example, a stated 6,000 ft elevation limit may function perfectly well up to 4,000 ft. Then, possibly a gradual fall-off in accuracy between 4,000-5,000ft. But then a rapid and possibly logarithmic increase in error percentage over 5,000ft. This is just an example and not meant to be a basis for calculating decreasing accuracy in any scientific instrument.

The original analog barometer was the water ball. This instrument featured a glass reservoir at its bottom that fed into a narrowing tube that protruded upwards. As atmospheric pressure increased, the water was driven upwards into the tube, to indicate fair or improving weather conditions. Conversely, as the air pressure dropped, the water level in the tube fell, to indicate a change to more inclement weather. As the water level fell even lower in the tube, it became a more urgent indicator of impending foul weather.

Hurricanes and tornadoes are both natural disasters that produce powerful, destructive winds that spiral cyclonically inwards via low pressure (clockwise in the southern hemisphere, counterclockwise in the northern hemisphere).

Hurricanes have a calm, clear eye at the center of rotation and it is believed that many tornadoes have a similar feature.

Both have scales for rating intensity:

• Tornadoes are rated on the Fujita scale from F0 to F5 based on damage, some countries, including the United States have upgraded to the Enhanced Fujita scale (EF0 to EF5).
• Hurricanes are rated on the Saffir-Simpson scale from Category 1 to Category 5.

The instrument that measures humidity is called a hygrometer.

A hygrometer is an instrument that measures relative humidity in the air. One common kind of hygrometer is a psychrometer, a device that measures the temperature of a wet bulb and a dry bulb simultaneously. The wet bulb should be cooler (if it's above freezing), because water evaporates from the bulb, taking energy with it. If the air is more humid, the evaporation is slower, so the bulb is closer to the dry bulb's temperature. A comparison of the wet and dry bulb temperature using a Psychrometric Chart indicates the relative humidity of the air.

Hygrometers can be combined with other systems as the sensor to regulate humidity. The resulting instrument may be called a humidistat or hygristor, which function somewhat like a thermostat adding or subtracting moisture, not heat, to the air. Types of Hygrometers include:

• a dry bulb thermometer and a wet bulb thermometer with a Psychrometric chart

• A hygrograph which gives a continuous record of the humidity value using human hair, on a graph

• A hygristor using lithium chloride is used to find out the humidity values at different altitudes. Hygristor's resistance varies with the humidity and this principle is used to find out the humidity.

• A humidity indicator card (HIC) is a card on which a moisture-sensitive chemical is impregnated such that it will change color as the humidity changes

In term of units; humidity can be expressed by

• Absolute humidity: total moisture/volume of air

• Relative humidity: total moisture/saturated moisture

• Specific humidity: total moisture/weight of dry air

In term of method, Various equipment can be used to measure water content direct or indirectly.

• Direct measure by cooling the air down to condensation point.
• Indirect measure by measure air conductivity and related to presence of humidity. Infrared spectrometry is used to measure presence of moisture from IR absorption.

In term of equipment:

One device is known as a hygrometer. A hygrometer is used to measure humidity.

Not to be confused with the hydrometer which measures the specific gravity of liquids.

A Psychrometer is a type of Hygrometer. A psychrometer consists of two thermometers, one which is dry and one which is kept moist with distilled water on a sock or wick.

As an upgrade in technology there is the trace moisture sensor which is a phosphorous pentoxide (P205), a very hydrophilic material, the resistivity of which changes with the humidity, so it is used in electronic devices designed to make use of the property.

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Another tool that could be used is a Cyanometer, an instrument for measuring 'blueness', specifically the color intensity of blue sky. It is attributed to Horace-Bénédict de Saussure and Alexander von Humboldt. It consists of squares of paper dyed in graduated shades of blue and arranged in a color circle or square that can be held up and compared to the color of the sky. The blueness of the atmosphere indicates transparency and the amount of water vapor.

hygrometers and psychrometers

40 °C is equal to 104 °F

The conversion formula is Fahrenheit temperature = (9/5 x Celsius temperature)+ 32
40 degree Celsius = 104 degree Fahrenheit

• Atmospheric Scientists study weather, ozone, climate change and pollution of the atmosphere.
• Climatologists study climates.
• Meteorologists study the atmosphere and weather.
• Operational Meteorologists forecast the weather.
• Physical Meteorologists study the properties of the atmosphere, the transmission of light, sound and radio waves, and the factors that affect the formation of weather.
• Synoptic Meteorologists develop new tools for forecasting weather.

Atmospheric pressure at sea level is the result of the force of gravity on the matter above sea level (the atmospheric gases). The amount of matter is not constant due to the height and density of the atmosphere (mostly due to temperature and water content/humidity).

Unfortunately for the student, there are many, many different units for measuring atmospheric pressure. Standard air pressure at sea level is most easily defined as 1 atmosphere, or 1 atm.

In terms of an international (ISO) standard, it is defined to be 101325 Pa or 101.3 kPa (kilo-Pascals) at a temperature of 15 °C. In meteorology outside of the United States (and sometimes among scientists in the USA), hPa (hectoPascal) is most commonly used (=1013.25 hPa)

Note that a Pascal is also equal to N/m2 - Newtons per square meter, while 1 hpa = 1 mb (millibar) which is convenient for meteorologists, as noted above. Therefore, standard atmospheric pressure also = 1.01325 bar = 1013.25 mb.

The metric value is commonly accepted to be 760mmHg(millimeters of mercury, also "torr"). "Millimeters of Mercury" is a measure that come from a kind of barometer (pressure meter) that uses a column of mercury in a glass tube to measure pressure: The higher the pressure, the taller the column of mercury.

In American units of measure, it's 29.92 in. Hg (inches of mercury) or 14.696 psi (pounds per square inch). This means that, at sea level, the weight of air pressing on every square inch of something is almost 15 pounds.

Something to think about: If you had 1 square inch of room-temperature mercury that was 29.92" tall, it would weigh ... 14.696 pounds!

Again, these are the average atmospheric pressures only at sea level. Pressure drops as we gain altitude; for instance, in Denver, approximately 1 mile above sea level, atmospheric pressure drops to approximately 12.2 PSI or 841.4 millibar.

If you were at sea level, the weight of the air pressing down on you would be 1.03 kilograms per square centimeter.or 1013.25 millibars.

The line where these two air masses meet is called a front.

• If cold air advances and pushes away the warm air, it forms a cold front.
• Cold fronts are associated with rain following the front itself.

• When warm air advances, it rides up over the denser, cold air mass to form a warm front.
• Warm fronts are associated with rain leading the front itself.
• If neither air mass advances, it forms a stationary front.
• If dry air advances into moist air and there is no significant temperature difference, it forms a dry line.
• It is not uncommon to see severe thunderstorms develop along cold fronts and dry lines.

20°C is equal to 68°F

The conversion formula is °F = (9/5 °C)+ 32

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F = [20 * (9/5)] + 32

F = 36 + 32

F = 68.
It's easy to convert from Celsius to Fahrenheit by yourself. Tf = (9/5)*Tc+32, where Tc = temperature in degrees Celsius, Tf = temperature in degrees Fahrenheit.20 C is 68 F.
20 degrees Celsius is 68 degrees Fahrenheit.
Conversion from Celsius to Fahrenheit is done in three steps:

1. Multiply value in degrees Celsius by 9.

2. Divide result of step 1 by 5.

3. Add 32 to result of step 2.

Conversion formula: [°F] = [°C] * 9 / 5 + 32 = 20 * 9 / 5 + 32 = 68 °F
68 F

In the United States, the vernal equinox, which signifies the start of astronomical spring in the northern hemisphere, actually happens on March 19, 20, or 21 each year. We haven’t had a March 19 equinox since 1896, and we won’t have a March 21 equinox until 2101.

I say it marks the beginning of astronomical spring because meteorological spring (based on weather patterns) starts March 1.

Astronomical spring is a little harder to explain. The Earth’s axis is always tilted at about 23 degrees, meaning that depending on where it is in its orbit, one hemisphere or the other is closer to the sun. The equinoxes (the vernal equinox in March and the autumnal equinox in September) mark the points in the orbit where neither hemisphere is tilted toward nor away from the sun, meaning day and night are nearly equal.

Cold fronts are defined by cold air advancing, sliding under and displacing warmer air - they are steeper and move more quickly.

Warm air cannot displace cold air easily because it is less dense. Therefore, it rides up and over it, producing stratus and nimbostratus clouds where light precipitation falls.
the boundary of an advancing mass of warm air, in particular the leading edge of the warm sector of a low-pressure system.