One of the stalwart units of astronomy just got a makeover. The International Astronomical Union, the authority on astronomical constants, has voted unanimously to redefine the astronomical unit, the ...

A light-year or lightyear (symbol: ly) is a unit of measurement of length, specifically the distance light travels in a vacuum in one year. While there is no authoritative decision on which year is ...

Click anywhere on this site, and you’ll likely run into a measurement in terms of light-years, solar masses, astronomical units, or arcminutes. These units are unique to astronomy, and all can be ...

Scientists still define astronomical time in years, with some recent refinements. By C. Claiborne Ray Q. Do scientists actually speak of the age of the universe in years, or do they use some ...