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A light-year, alternatively spelled light year (ly or lyr [3]), is a unit of length used to express astronomical distances and is equal to exactly 9 460 730 472 580.8 km, which is approximately 9.46 trillion km or 5.88 trillion mi.
Precessional movement of Earth. Earth rotates (white arrows) once a day around its rotational axis (red); this axis itself rotates slowly (white circle), completing a rotation in approximately 26,000 years [1] In astronomy, axial precession is a gravity-induced, slow, and continuous change in the orientation of an astronomical body's rotational ...
A megaparsec is one million parsecs, or about 3,260,000 light years. [22] Sometimes, galactic distances are given in units of Mpc/ h (as in "50/ h Mpc", also written " 50 Mpc h −1 "). h is a constant (the " dimensionless Hubble constant ") in the range 0.5 < h < 0.75 reflecting the uncertainty in the value of the Hubble constant H for the ...
A light-year is the distance light travels in one Julian year, around 9461 billion kilometres, 5879 billion miles, or 0.3066 parsecs. In round figures, a light year is nearly 10 trillion kilometres or nearly 6 trillion miles. Proxima Centauri, the closest star to Earth after the Sun, is around 4.2 light-years away. [90]
≈ 1 hour walk, Currently defined in US as 3 Statute miles, [3] but historically varied from 2 to 9 km ≈ 4828 m: light-day: ≡ 24 light-hours ≡ 2.590 206 837 12 × 10 13 m: light-hour: ≡ 60 light-minutes ≡ 1.079 252 8488 × 10 12 m: light-minute: ≡ 60 light-seconds ≡ 1.798 754 748 × 10 10 m: light-second: ≡ Distance light ...
An illustration of light sources from magnitude 1 to 3.5, in 0.5 increments In astronomy , magnitude is a measure of the brightness of an object , usually in a defined passband . An imprecise but systematic determination of the magnitude of objects was introduced in ancient times by Hipparchus .
Distance measures are used in physical cosmology to give a natural notion of the distance between two objects or events in the universe.They are often used to tie some observable quantity (such as the luminosity of a distant quasar, the redshift of a distant galaxy, or the angular size of the acoustic peaks in the cosmic microwave background (CMB) power spectrum) to another quantity that is ...
1.2 Em – 129 light-years – diameter of Messier 13 (a typical globular cluster) 1.6 Em – 172 ± 12.5 light-years – diameter of Omega Centauri (one of the largest-known globular clusters, perhaps containing over a million stars) [199] [200] 3.08568 Em – 326.1 light-years – 1 hectoparsec