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April Fool's Day
(Encyclopedia)April Fool's Day or All Fool's Day, holiday of uncertain origin, known for practical joking and celebrated on the first of April. Prior to the adoption of the Gregorian calendar in 1564, the date was ...Taconic Mountains
(Encyclopedia)Taconic Mountains təkŏnˈĭk [key], range of the Appalachian Mts., extending c.150 mi (240 km) north-south between the Green Mts. and the Hudson Valley along parts of New York's border with Vermont,...tropical year
(Encyclopedia)tropical year, time between successive vernal equinoxes; 365 days, 5 hr, 48 min, 46 sec of mean solar time (see solar time). The tropical year is the basis of the year used in the Gregorian calendar. ...New Year's Day
(Encyclopedia)New Year's Day, among ancient peoples the first day of the year frequently corresponded to the vernal or autumnal equinox, or to the summer or winter solstice. In the Middle Ages it was celebrated amo...day
(Encyclopedia)day, period of time for the earth to rotate once on its axis. The ordinary day, or solar day, is measured relative to the sun, being the time between successive passages of the sun over a stationary o...hour angle
(Encyclopedia)hour angle, in astronomy, a coordinate in the equatorial coordinate system. The hour angle of a celestial body is the angular distance, expressed in hours, minutes, and seconds (one hour equals 15 deg...Gill, Sir David
(Encyclopedia)Gill, Sir David gĭl [key], 1843–1914, Scottish astronomer, educated at the Univ. of Aberdeen. He made observations of the transits of Venus and Mars and investigated the solar parallax. As astronom...Pisces
(Encyclopedia)Pisces pīˈsēz [key] [Lat.,=the fishes], constellation lying directly S of Andromeda and on the ecliptic (the sun's apparent path through the heavens) between Aries and Aquarius; it is one of the co...sidereal time
(Encyclopedia)sidereal time (ST), time measured relative to the fixed stars; thus, the sidereal day is the period during which the earth completes one rotation on its axis so that some chosen star appears twice on ...cycle
(Encyclopedia)cycle, in astronomy, period of time required for the recurrence of some celestial event. The length of a cycle may be measured relative to the sun or to the fixed stars (see sidereal time). A frequent...Browse by Subject
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