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Giacconi, Riccardo

(Encyclopedia)Giacconi, Riccardo, 1931–2018, Italian-American astrophysicist, b. Milan, Italy, Ph.D. Univ. of Milan 1954. He was a researcher at American Science and Engineering Corporation (1959–73), professor...

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. ...

Lockyer, Sir Joseph Norman

(Encyclopedia)Lockyer, Sir Joseph Norman lŏkˈyər [key], 1836–1920, English astronomer, educated on the Continent. One of the first to make a spectroscopic examination of the sun and stars, he devised (1868), i...

sidereal year

(Encyclopedia)sidereal year, time required for the earth to complete an orbit of the sun relative to the stars. The sidereal year is 365 days, 6 hr, 9 min, 9.5 sec of mean solar time (see solar time). It is 20 min ...

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...

SETI

(Encyclopedia)SETI sĕtˈē [key] [Search for ExtraTerrestrial Intelligence], name given to a series of independent programs to detect radio signals from civilizations beyond the solar system. Modern SETI efforts c...

chromosphere

(Encyclopedia)chromosphere krōˈməsfērˌ [key] [Gr.,=color sphere], layer of rarefied, transparent gases in the solar atmosphere; it measures 6,000 mi (9,700 km) in thickness and lies between the photosphere (th...

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...

celiac plexus

(Encyclopedia)celiac plexus: see solar plexus. ...

Sedna

(Encyclopedia)Sedna, in astronomy, the most distant known large object in the solar system. With a highly eccentric elliptical orbit that ranges from an estimated 76 AU to 937 AU, Sedna also has an extremely long o...