Astrophysics (Index)About

astronomical quantities

(some astronomy amounts/numbers)

These are astronomical quantities such as distances and counts to hint at the scales of things in astronomy and give some sense regarding a quantity such as 100 Mpc. See "Wavelengths table" for electromagnetic radiation band ranges and "Distances table" for distances and redshifts. See "redshift" for relation between distance and redshift. See "spectral class" and "luminosity class" for stellar classifications and "extra-solar planet" for various types of planets. See "Lambda-CDM model" for its parameters. Regarding distance scales:

light-year (ly) 63241 AU 9.461×1015m or 5.879×1012 miles
parsec 3.262 ly 206,265 AU, 3×1016m or 1.917×1013 miles
speed of light 186,000 miles/sec 300,000 km/sec
Earth radius 3959 miles 6371 km
Earth mass 5.972×1024 kg
Earth orbital speed 30 km/sec 67100 MPH
Moon distance 238,900 miles 60 Earth radii, 0.55 solar radius or 0.0025 AU
Moon radius 1079 miles 0.27 Earth radius (1/4) or 1737 km
Moon mass 7.3×1022 kg 0.012 Earth mass (1.2%)
Moon orbital speed 1 km/s 2200 MPH
Sun distance 93 million miles 215 solar radii or 1 AU
Sun radius 432,288 miles 109 Earth radii or 0.0047 AU
Sun mass 2×1030 kg 334,000 Earth masses
Jupiter orbit radius 483.8 million miles 5.2 AU
Jupiter radius 43441 miles 11 Earth radii or 1/10 solar radius
Jupiter mass 1.898×1027 kg 318 Earth masses or 0.001 solar mass (0.1%)
Neptune orbit radius 2.795 billion miles 30 AU, 0.0005 ly or 4hr10min × c
Neptune radius 15299 miles 3.85 Earth radii or 0.035 solar radius (3.5%)
Neptune mass 1026 kg 17 Earth masses or 0.00005 solar mass (0.005%)
Alpha Centauri distance 4.367 ly 9200 × Neptune's orbit radius
galactic center distance 26000 ly 8.2 kpc or 6000 × distance to Alpha Centauri
Milky Way number of stars 100-400 billion
Milky Way visible diameter 100,000 ly 30 kpc
Milky Way visible depth 10,000 ly 3 kpc
Milky Way galactic halo diameter 300,000-400,000 ly 100 kpc
Canis Major Dwarf Galaxy distance (claimed nearest galaxy) 25000 ly 8 kpc
Sagittarius Dwarf Elliptical Galaxy (accepted nearest galaxy) 65000 ly 20 kpc
Andromeda distance (nearest similar galaxy) 2.5 million ly 765 kpc, 0.8 Mpc or 25 Milky Way diameters
Local Group diameter 10 Mly 3 Mpc or 100 Milky Way diameters
Local Group galaxy count ~100
Virgo Cluster (nearest galaxy cluster) distance 53 Mly 16 Mpc
Virgo cluster galaxy count 1000-2000
Virgo Supercluster diameter 110 Mly 34 Mpc
Virgo supercluster cluster/group count 100
Virgo supercluster galaxy count 47000
Laniakea Supercluster diameter 520 Mly 160 Mpc or distance to z = 0.04
Laniakea cluster count 300-500
Laniakea galaxy count 100,000
typical stars per galaxy 100 million to 100 trillion
superclusters in observable universe estimated 10 million
galaxies in observable universe estimated 170 billion
stars in the observable universe estimated 1024 (septillion)
age of universe 13.77 gigayears
diameter of observable universe 93 Gly 28.5 Gpc or 180 × Laniakea diameter
mass of observable universe estimated 1053kg
visible light wavelengths 4000-7000 angstroms 4×10-7 to 7×10-7 meters
atoms in a gram of hydrogen (Avogadro's number) 6.022×1023
atoms in the universe estimated 1078 to 1082
photons in the universe estimated 1089
neutrino density 340/cm3
neutrinos in the universe estimated 1.2×1089
atomic density of the universe (baryonic mass density) estimated 0.2-0.25 hydrogen atoms/meter3
critical density of the universe estimated 5 hydrogen atoms/meter3 threshold between eventual expansion versus collapse
density including dark matter and dark energy roughly same very close to critical density

Some of the counts have varying estimates ranging over an order-of-magnitude or more, and subject to substantial improvement over time, in which case the above numbers are no more than example estimates. This is true of some of the distances and masses beyond those within the solar system, and some of the item counts for galaxies, galaxy groups, clusters, superclusters, and the entire observable universe.

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