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International Geophysical Year

(Encyclopedia)International Geophysical Year (IGY), 18-month period from July, 1957, through Dec., 1958, during a period of maximum sunspot activity, designated for cooperative study of the solar-terrestrial enviro...

Stonehenge

(Encyclopedia)Stonehenge stōnˈhĕnjˌ [key], group of standing stones on Salisbury Plain, Wiltshire, S England. Preeminent among megalithic monuments in the British Isles, it is similar to an older and larger mon...

planetarium

(Encyclopedia)planetarium, optical device used to project a representation of the heavens onto a domed ceiling; the term also designates the building that houses such a device. A modern planetarium consists of as m...

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...

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...

Lacaille, Nicolas Louis de

(Encyclopedia)Lacaille, Nicolas Louis de nēkôläˈ lwē də läkäˈyə [key], 1713–62, French astronomer. As a result of his success in making meridional measurements in France under the patronage of the duke ...

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...

Pickering, William Henry

(Encyclopedia)Pickering, William Henry, 1858–1938, American astronomer, b. Boston, grad. Massachusetts Institute of Technology (B.S., 1879). He taught at the Massachusetts Institute of Technology (1880–87) and ...

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...

cosmology

(Encyclopedia)cosmology, area of science that aims at a comprehensive theory of the structure and evolution of the entire physical universe. The earliest pre-Ptolemaic theories assumed that the earth was the cent...