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a group of bright stars which form a conspicuous pattern on the celestial sphere
Industry:Astronomy
Also called planetoids or minor planets, the asteroids are tiny planets most of which orbit the Sun between Mars and Jupiter. The largest - and the first discovered - is Ceres, with a diameter of 1,003 km. It is estimated that there may altogether be no fewer than 40000. A few have very elliptical orbits and cross the orbits of several other (major) planets. One or two even have their own satellites (moons.)
Industry:Astronomy
A region of space lying between Mars (1.5 AU) and Jupiter (5.2 AU), where the great majority of the asteroids are found. None of the belt asteroids have retrograde motion.
Industry:Astronomy
1) Divination using the positions of the planets, the Sun and the Moon as seen against the stars in the constellations of the zodiac - a "science" almost as old as homo sapiens. Although at one stage in history astrology and astronomy were almost synonymous- the latter has advanced so far during the last three centuries that the two now bear little relation to each other.
2) The belief that human affairs and people's personalities and characters are influenced by (or encoded in) the positions of the planets.
Industry:Astronomy
In the orbit of a solar-system body, the point where the body crosses the ecliptic from south to north: for a star, out of the plane of the sky toward the observer.
Industry:Astronomy
An optical surface with departures in shape from a perfect sphere in order to cancel optical imperfections or aberrations.
Industry:Astronomy
The branch of astronomy that deals with measuring the positions of celestial objects, especially stars. Astrometrists measure parallaxes and proper motions, which allow astronomers to determine the distances and velocities of the stars.
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
