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ultraviolet astronomy

(Encyclopedia)ultraviolet astronomy, study of celestial objects by means of the ultraviolet radiation they emit, in the wavelength range from about 90 to about 350 nanometers. Ultraviolet (UV) line spectrum measure...

radio astronomy

(Encyclopedia)radio astronomy, study of celestial bodies by means of the electromagnetic radio frequency waves they emit and absorb naturally. Radio waves also come from outside the Milky Way. These extragalact...

transit

(Encyclopedia)transit, in astronomy, passage of a body across a meridian or passage of a small body across the visible disk of a larger one. (The passage of a large body across a smaller one is called an eclipse or...

elongation

(Encyclopedia)elongation, in astronomy, the angular distance between two points in the sky as measured from a third point. The elongation of a planet is usually measured as the angular distance from the sun to the ...

gamma-ray astronomy

(Encyclopedia)gamma-ray astronomy, study of astronomical objects by analysis of the most energetic electromagnetic radiation they emit. Gamma rays are shorter in wavelength and hence more energetic than X rays (see...

X-ray astronomy

(Encyclopedia)X-ray astronomy, study of celestial objects by means of the X rays they emit, in the wavelength range from 0.01 to 10 nanometers. X-ray astronomy dates to 1949 with the discovery that the sun emits X ...

retrograde motion

(Encyclopedia)retrograde motion, in astronomy, real or apparent movement of a planet, dwarf planet, moon, asteroid, or comet from east to west relative to the fixed stars. The most common direction of motion in the...

Newcomb, Simon

(Encyclopedia)Newcomb, Simon no͞oˈkəm, nyo͞oˈ– [key], 1835–1909, American astronomer, b. Nova Scotia, grad. Lawrence Scientific School, Harvard, 1858. Living in the United States from 1853, he was appointe...

Horrocks, Jeremiah

(Encyclopedia)Horrocks or Horrox, Jeremiah both: hŏrˈəks [key], 1618?–1641, English astronomer. He made the first observation of the transit of Venus. His Venus in sole visa, which narrates this experience, wa...

Sagan, Carl Edward

(Encyclopedia)Sagan, Carl Edward sāˈgən [key], 1934–96, American astronomer and popularizer of science, b. New York City. Early in his career he investigated radio emissions from Venus and concluded that the c...