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Related to astronomical: Astronomical twilight, Astronomical Unit


Of or pertaining to astronomy or to observations of the celestial bodies. Also known as astronomic.

tropical year

tropical yearclick for a larger image
The period between two successive vernal equinoxes, the time the earth takes to complete one orbit around the sun relative to the first point of Aries. Its length was 365 days 5 h 48 min and 45.19 s in 2000, and it is changing by 0.00000006162 x y days (y in Julian years from 2000), or about 5 milliseconds/year. The tropical year differs from the solar year by 1 part in 26,000, since this is the period of the earth's precession about its rotational axis combined with the precession of the perihelion of the earth's orbit. Also called an astronomical, equinoctial, natural, or solar year. It contains one complete cycle of seasons.


The period of incomplete darkness following sunset and preceding sunrise. Twilight is designated as civil, nautical, or astronomical, as the darker limit occurs when the center of the sun is 6°, 12°, and 18°, respectively, below the celestial horizon. The period of civil twilight before sunrise is known as morning civil twilight and after the sunset as evening civil twilight. The air almanac lists the local mean times of the beginning of morning civil twilight and the end of evening civil twilight in exactly the same format as sunrise and sunset tables. The twilight tables are printed on the right-hand pages facing the sunrise and sunset tables, with each pair covering the same block of calendar dates.
References in periodicals archive ?
The stations, the locations of which have been posted by Philippine Astronomical Society Inc.
Astronomical Society of the Pacific Conference Series; Volume 501
Astronomical Blue Moons happen either once every two to three years or so, depending on which of the two definitions you apply.
It is operated through computer networks and astronomical software," Salam added.
Xi and Uzbekistan's President Islam Karimov agreed that scientists of the two countries should carry out cooperation in astronomical study.
Cunningham said the recent study of the 25,000 to 30,000 year oldDolni Vestonice Venus and the around 5,000 Year old Cypriot 'Lemba Lady' had confirmed that linear marks drawn on the back and front of late Paleolithic-era figures were an astronomical/geometrical text used to represent astronomical values.
Astronomical Data Analsis Software and Systems (22nd: 2012: Champaign, Illinois) Ed.
For a few years afterwards we used to meet up once a year when I came to Coventry on astronomical business.
This programme received good feedback from other astronomical societies in the USA and the UK.
Since the observations of distant astronomical objects correspond to past time, the rest masses of the material particles in these objects are smaller than the corresponding masses we measure in the laboratory, due to the selfvariations.
One might think that astronomers would have had the whole 'distance from the Earth to the sun' matter locked up a while back, but it turns out that the astronomical unit has been a contentious figure for centuries.
Robert Williams, President, International Astronomical Union (IAU), for its impressive, voluntary awareness drive to educate people in the UAE about astronomical phenomena.