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physical object > natural object > celestial body > star > double star

double star
subject			fact

double star	has definition A "system" of two stars that appear - because of coincidental alignment when viewed from Earth - to be close together; it is, however, an optical effect only, and therefore not the same as a binary star system (although until the twentieth century there were few means of distinguishing double and binary stars).
	is a kind of star
star	has star surface temperature
	has spectral type
	has V magnitude
	has B magnitude
	has U magnitude
	has position on celestial sphere from the point of view of Earth
	has parallax from the point of view of Earth's orbit
	has proper motion
	has radiation at surface which is diffused out from the hotter core
	has energy source gravitational contraction and or fusion
	has energy production which takes place primarily within the core
	has surface density which depends on luminosity class
	has surface temperature greater than 1000 Kelvin
	has apparent magnitude
	has absolute magnitude
	has age
	has catalog star catalog
	has material hydrogen, helium
	has velocity determined from proper motion and radial velocity
	has mass greater than 0.08 the sun's mass
celestial body	has spectra
physical object	has location or center of gravity
	has angular momentum
	has momentum
	has temperature
	has volume
	has extent

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