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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...

gegenschein

(Encyclopedia)gegenschein gāˈgənshīnˌ [key] or counterglow, a slight brightening of the night sky in the region of the zodiac directly opposite the sun, i.e., 180° from the sun. Discovered by the Danish astro...

ephemeris time

(Encyclopedia)ephemeris time (ET), astronomical time defined by the orbital motions of the earth, moon, and planets. The earth does not rotate with uniform speed, so the solar day is an imprecise unit of time. Ephe...

actinometer

(Encyclopedia)actinometer ăkˌtənŏmˈətər [key], instrument used to measure the heating power of radiation. Actinometers are used chiefly in meteorology to measure solar radiation as transmitted directly by th...

terrestrial planet

(Encyclopedia)terrestrial planet, the earth or a planet that resembles the earth in its physical characteristics. The terrestrial planets in the solar system are the earth, Mercury, Venus, and Mars. These planets a...

Birkeland, Kristian

(Encyclopedia)Birkeland, Kristian or Olaf Christian krĭsˈtyän bērˈkəlän, ōˈläv [key], 1867–1917, Norwegian physicist. From 1898 Birkeland was a professor at the Univ. of Christiania (now Oslo). Noted fo...

Bode, Johann Elert

(Encyclopedia)Bode, Johann Elert yōˈhän āˈlĕrt bōˈdə [key], 1747–1826, German astronomer. From 1772 to 1825 he was astronomer of the Academy of Science, Berlin, and from 1786, director of the Berlin Obse...

Wovoka

(Encyclopedia)Wovoka wōvōˈkə [key], c.1858–1932, Paiute, prophet of a messianic religion sometimes called the Ghost Dance religion. Also known as Jack Wilson, he was influenced by his father (a mystic) as wel...

Julian Day calendar

(Encyclopedia)Julian Day calendar, system of astronomical dating that allows the difference between two dates to be calculated more easily than conventional civil calendars with their uneven months. It was devised ...

Alentejo

(Encyclopedia)Alentejo əlāntāˈzho͝o [key], historic province, SE Portugal, now divided into Altro (Upper) Alentejo (4,888 sq mi/12,660 sq km) and Baixo (Lower) Alentejo (5,318 sq mi/13,774 sq km). The capital ...