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The time and azimuth at which a celestial body crosses the astronomical horizon of an oberver.
Industry:Astronomy
The change in direction of travel (bending) of a light ray as it passes obliquely through the atmosphere. As a result of refraction, the observed altitude of a celestial object is greater than its geometric altitude. The amount of refraction depends on the altitude of the object and on atmospheric conditions.
Industry:Astronomy
1) Mean distance between the Earth and the Sun: 1.495985 × 1011 m.
2) The AU is the preferred unit for distances within the solar system. Mercury, the innermost planet, lies on average 0.39 AU from the Sun; Pluto, normally the farthest planet, lies on average 39.5 AU from the Sun.
3) The mean distance between the Earth and the Sun. The astronomical unit is defined as the length of the radius of the unperturbed circular orbit of a body of negligible mass moving around the Sun with a sidereal angular velocity of 0.017202098950 radian per day of 86400 ephemeris seconds. AU = 1.496 × 1013 cm ≈ 500 lt-sec.
4) The mean distance from the earth to the sun, equal to 92.81 million miles or 499.012 light-seconds.
5) The radius of a circular orbit in which a body of negligible mass, and free of perturbations, would revolve around the Sun in 2π / k days, where k is the Gaussian gravitational constant. This is slightly less than the semi-major axis of the Earth's orbit.
Industry:Astronomy
The science that studies the physics and chemistry of extraterrestrial objects. The alliance of physics and astronomy, which began with the advent of spectroscopy, made it possible to investigate what celestial objects are and not just where they are.
Industry:Astronomy
Globular cluster stars, which are found in that part of the HR diagram that connects the top pf the giant tip with the horizontal branch stars.
Industry:Astronomy
volatile element that tends to be found in the atmosphere of a planet or asteroid
Industry:Astronomy
Mantle of gases round a star planet or moon, sometimes even forming the apparent surface of the body. For a body to retain an atmosphere depends on the body's gravity, and the temperature and composition of the gases. Mean atmospheric pressure at the surface is 10330 kg/m2, and is also referred to as atmosphere.
Industry:Astronomy
An optical device usually comprising two thin prisms which can rotate to compensate for the elongation of a star image caused by the wavelength dependence of the refractive index of air.
Industry:Astronomy
Decrease in the intensity of light from a celestial body due to absorption and scattering by the Earth's atmosphere. The extinction increases from the zenith to the horizon and affects short wavelengths more than long wavelengths, so that objects near the horizon appear redder than they are at the zenith.
Industry:Astronomy
