- 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.
- Astronomical unit
a unit of length, equal to the mean distance of the earth from the sun: approximately 93 million miles (150 million km). Abbreviation: AU. Historical Examples That was one astronomical unit, equal to about ninety-three million miles, the distance from Earth to the sun. Rip Foster in Ride the Gray Planet Harold Leland Goodwin In […]