atmospheric refraction. Drawing, description

CHILDREN'S SCIENTIFIC LABORATORY
Free library / Directory / Children's Science Lab

atmospheric refraction. Children's Science Lab

Children's Science Lab

atmospheric refraction called the deviation of light rays from a straight line when they pass through the atmosphere due to changes in air density with height. Atmospheric refraction near the earth's surface creates mirages and can cause distant objects to appear flickering, trembling, above or below their true position. In addition, the shape of objects may be distorted - they may appear flattened or stretched. Term "refraction" The same applies to the refraction of sound.

atmospheric refraction is the reason that astronomical objects rise above the horizon somewhat higher than they actually are. Refraction affects not only light rays but all electromagnetic radiation, although to varying degrees. For example, in visible light, blue is more susceptible to refraction than red. This can cause astronomical objects to appear in a spectrum in high resolution images.

Whenever possible, astronomers plan their observations when the celestial body passes the upper culmination point, when it is highest above the horizon. Also, when determining the coordinates of the vessel, sailors will never use a luminary whose height is less than 20 ° above the horizon. If the observation of a star close to the horizon cannot be avoided, then the telescope can be equipped with control systems to compensate for the displacement caused by the refraction of light in the atmosphere. If dispersion is also a problem (in the case of using a broadband camera for high resolution observations), then atmospheric refraction correction can be used (using a pair of rotating glass prisms). But since the degree of atmospheric refraction depends on temperature and pressure, as well as humidity (the amount of water vapor, which is especially important when observing in the middle of the infrared region of the spectrum), the amount of effort required to successfully compensate can be prohibitive.

atmospheric refraction interferes with observations most when it is not homogeneous, such as when there is turbulence in the air. This causes the stars to twinkle and distort the apparent shape of the sun at sunset and sunrise.

Atmospheric refraction values

atmospheric refraction equal to zero at the zenith, less than 1' (one minute of arc) at an apparent height of 45° above the horizon, and reach a value of 5,3' at 10° height; refraction increases rapidly with decreasing altitude, reaching 9,9' at 5° altitude, 18,4' at 2° altitude, and 35,4' at the horizon (1976 Allen, 125); all values obtained at 10°C and atmospheric pressure 101,3 kPa.

At the horizon, the amount of atmospheric refraction is slightly greater than the apparent diameter of the Sun. Therefore, when the full disk of the sun is visible just above the horizon, it is visible only due to refraction, since if there were no atmosphere, then not a single part of the solar disk would be visible.

In accordance with the accepted convention, the time of sunrise and sunset is attributed to the time when the upper edge of the Sun appears or disappears above the horizon; the standard value for the true altitude of the Sun is -50'...-34' for refraction and -16' for the half diameter of the Sun (height of a celestial body is usually given for the center of its disk). In the case of the Moon, additional corrections are needed to take into account the horizontal parallax of the Moon and its apparent half-diameter, which varies with the distance of the Earth-Moon system.

Daily weather changes affect the exact time of sunrise and sunset of the sun and moon (see the article "Refraction at the horizon"), and for this reason it makes no sense to give the time of apparent sunset and sunrise with an accuracy greater than a minute of arc (this is described in more detail in Astronomical Algorithms, Jean Meeus, 1991, p. 103). More accurate calculations may be useful in determining day-to-day variations in sunrise and sunset times using standard refractivity values, since it is understood that actual changes may differ due to unpredictable changes in refractivity.

Because of atmospheric refraction is 34' at the horizon, and only 29 minutes of arc at 0,5° above the horizon, at sunset or sunrise it appears to be flattened by about 5' (which is about 1/6 of its apparent diameter).

Calculation of atmospheric refraction

A rigorous calculation of refraction requires numerical integration using this method described in the paper by Auer and Standish Astronomical refraction: calculation for all zenith angles, 2000. Bennett (1982) in his article "Calculation of astronomical refraction for marine navigation applications" derived a simple empirical formula for determining the magnitude of refraction as a function of the apparent height of luminaries, using the algorithm of Garfinkel (1967) as a reference , If h_a - this is the apparent height of the luminary in degrees, then the refraction R in arc minutes will be equal to

the accuracy of the formula is up to 0,07' for heights from 0° to -90° (Meeus 1991, 102). Smardson (1986) developed a formula for determining the refraction relative to the true height of the stars; If h is the true height of the star in degrees, then the refraction R in arc minutes is

the formula agrees with the Bennett formula to within 0.1'. Both formulas will be true at an atmospheric pressure of 101,0 kPa and a temperature of 10 ° C; for different pressures Р and temperature Т the result of the calculation of refraction, made according to these formulas, should be multiplied by

(according to Meeus, 1991, 103). The refraction increases by about 1% for every 0,9 kPa increase in pressure and decreases by about 1% for every 0,9 kPa decrease in pressure. Similarly, refraction increases by about 1% for every 3°C decrease in temperature, and refraction decreases by about 1% for every 3°C rise in temperature.

Plot of refraction magnitude versus height (Bennett, 1982)

Random atmospheric effects caused by refraction

Atmospheric turbulence increases and decreases the apparent brightness of stars, making them brighter or fainter in milliseconds. The slow components of these oscillations are visible to us as flicker.

In addition, turbulence causes small random movements in the visible image of the star, and also produces rapid changes in its structure. These effects are not visible to the naked eye, but are easy to see even with a small telescope.

We recommend interesting articles Section Children's Science Lab:

▪ The power of rust

▪ Humidity measurement

▪ Astronomical instrument Observer

See other articles Section Children's Science Lab.

Read and write useful comments on this article.

<< Back

Latest news of science and technology, new electronics:

Artificial leather for touch emulation 15.04.2024

In a modern technology world where distance is becoming increasingly commonplace, maintaining connection and a sense of closeness is important. Recent developments in artificial skin by German scientists from Saarland University represent a new era in virtual interactions. German researchers from Saarland University have developed ultra-thin films that can transmit the sensation of touch over a distance. This cutting-edge technology provides new opportunities for virtual communication, especially for those who find themselves far from their loved ones. The ultra-thin films developed by the researchers, just 50 micrometers thick, can be integrated into textiles and worn like a second skin. These films act as sensors that recognize tactile signals from mom or dad, and as actuators that transmit these movements to the baby. Parents' touch to the fabric activates sensors that react to pressure and deform the ultra-thin film. This ... >>

Petgugu Global cat litter 15.04.2024

Taking care of pets can often be a challenge, especially when it comes to keeping your home clean. A new interesting solution from the Petgugu Global startup has been presented, which will make life easier for cat owners and help them keep their home perfectly clean and tidy. Startup Petgugu Global has unveiled a unique cat toilet that can automatically flush feces, keeping your home clean and fresh. This innovative device is equipped with various smart sensors that monitor your pet's toilet activity and activate to automatically clean after use. The device connects to the sewer system and ensures efficient waste removal without the need for intervention from the owner. Additionally, the toilet has a large flushable storage capacity, making it ideal for multi-cat households. The Petgugu cat litter bowl is designed for use with water-soluble litters and offers a range of additional ... >>

The attractiveness of caring men 14.04.2024

The stereotype that women prefer "bad boys" has long been widespread. However, recent research conducted by British scientists from Monash University offers a new perspective on this issue. They looked at how women responded to men's emotional responsibility and willingness to help others. The study's findings could change our understanding of what makes men attractive to women. A study conducted by scientists from Monash University leads to new findings about men's attractiveness to women. In the experiment, women were shown photographs of men with brief stories about their behavior in various situations, including their reaction to an encounter with a homeless person. Some of the men ignored the homeless man, while others helped him, such as buying him food. A study found that men who showed empathy and kindness were more attractive to women compared to men who showed empathy and kindness. ... >>

Random news from the Archive

DPP-3 - TDK-Lambda three-phase DIN rail power supplies 31.01.2011

The DPP-3 series consists of 4 power ratings: 120, 240, 480 or 960 W with output voltages of 12, 24, 48 V and is designed for industrial automation, measurement and control systems, distributed power systems. The DPP-3 power supplies operate on a 3-phase AC mains in the range 340...575 V, frequency 47...63 Hz without the need for switching or adjustment.

Each model contains a power factor corrector. An important property of the series is two-phase performance: if one phase fails, the unit will continue to work with a power reduction of up to 80%!

The output voltage of the module can be adjusted using the potentiometer on the front panel. This is necessary to compensate for the voltage drop in the power conductors to the load. Parallel connection of 2 modules is possible to increase power.

Load instability with parallel connection is + 5%, with single operation - + 1%. For added convenience in automation and control applications, the 24V models have an output voltage monitoring relay.

Other interesting news:

▪ Super hydrophobic material

▪ A rift has formed in Africa that could tear the continent apart

▪ The female brain changes every month

▪ Micro robot with a brush

▪ Gene rejuvenation

News feed of science and technology, new electronics

Interesting materials of the Free Technical Library:

▪ section of the site RF power amplifiers. Article selection

▪ article Emergencies in case of accidents at chemically hazardous facilities. Basics of safe life

▪ article What is aphid? Detailed answer

▪ article Chief mechanic of a car dealership. Job description

▪ article Lacquer for gilded baguettes. Simple recipes and tips

▪ article Moving a bottle and a glass. Focus secret

Leave your comment on this article:

All languages of this page

Home page | Library | Articles | Website map | Site Reviews