a frame of reference in which the sun or center of mass of the universe is fixed and which does not rotate with respect to the fixed stars.
- Astronomical refraction
- Astronomical telescope
a telescope having an objective with a long focal length and an eyepiece with a short focal length, usually used for observing celestial bodies. Historical Examples Kepler, in 1611, made the first astronomical telescope with two concave glasses. Astronomical Myths John F. Blake One word about the inversion of objects by the astronomical telescope. Half-hours […]
- Astronomical triangle
the spherical triangle formed by the great circles connecting a celestial object, the zenith, and the celestial pole.
- Astronomical twilight
either of two periods of partial darkness, after sunset or before sunrise, when the center of the sun is more than 6° but less than 18° below the horizon.