Columbia Encyclopedia

Search results

500 results found

seasons

(Encyclopedia)CE5 The seasons are caused by the tilt of the earth's axis to the plane of its orbit about the sun. The Northern Hemisphere is tilted toward the sun in the summer and receives more direct rays than...

Young, Charles Augustus

(Encyclopedia)Young, Charles Augustus, 1834–1908, American astronomer, b. Hanover, N.H., grad. Dartmouth, 1853. He discovered the reversing layer of the solar atmosphere and proved the gaseous nature of the sun's...

luminosity

(Encyclopedia)luminosity, in astronomy, the rate at which energy of all types is radiated by an object in all directions. A star's luminosity depends on its size and its temperature, varying as the square of the ra...

solar time

(Encyclopedia)solar time, time defined by the position of the sun. The solar day is the time it takes for the sun to return to the same meridian in the sky. Local solar time is measured by a sundial. When the cente...

solstice

(Encyclopedia)solstice sŏlˈstĭs [key] [Lat.,=sun stands still], in astronomy, either of the two points on the ecliptic that lie midway between the equinoxes (separated from them by an angular distance of 90°). ...

perihelion

(Encyclopedia)perihelion pĕrˌəhēˈlēən [key], point nearest the sun in the orbit of a body about the sun. See apsis. ...

solar wind

(Encyclopedia)solar wind, stream of ionized hydrogen—protons and electrons—with an 8% component of helium ions and trace amounts of heavier ions that radiates outward from the sun at high speeds. The continuous...

aphelion

(Encyclopedia)aphelion əfēˈlēən, ăpˌhēˈ– [key], point farthest from the sun in the orbit of a body about the sun. See apsis. ...

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 ...

astronomical unit

(Encyclopedia)astronomical unit (AU), mean distance between the earth and sun; one AU is c.92,960,000 mi (149,604,970 km). The astronomical unit is the principal unit of measurement within the solar system, e.g., M...