Astrophysics (index)

Astronomical Quantities

(some astronomy amounts/numbers)

These are Astronomical Quantities to hint at Astronomical Scales, to remind you what a quantity such as 100Mpc implies and how various quantities compare. See Wavelengths table for Electromagnetic Radiation (EMR) band ranges and Distances table for distances and redshifts. See "Redshift (z)" for relation between distance and redshift. See "Spectral Class" for stellar class parameters. See "Lambda-CDM model (ΛCDM)" for its parameters. Regarding distance scales:

  • Parsec (pc) - distances within the local stellar neighborhood, e.g., within Parallax range.
  • kpc - distances within the Milky Way.
  • Mpc - distances to other galaxies.
  • Gpc - distances over a substantial fraction of the universe.
ly (light year) 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 m/sec
Earth radius 3959 miles
Earth mass 5.972×1024 kg
Orbital Speed of the Earth 30km/sec 67100 MPH
Moon distance 238,900 miles 60 Earth radii, .55 solar radius or .0025 AU
Moon radius 1079 miles .27 Earth radius (1/4)
Moon mass 7.3×1022 kg .012 Earth mass (1.2%)
Moon orbital speed 1km/s 2200 MPH
Sun distance 93 million miles 215 solar radii or 1 AU
Sun radius 432,288 miles 109 Earth radii
Sun mass 2×1030 kg 334,000 Earth masses
Jupiter orbit radius 483.8 million miles 5.2AU
Jupiter radius 43441 miles 11 Earth radii or 1/10 solar radius
Jupiter mass 1.898×1027 kg 318 Earth masses or .001 solar mass (0.1%)
Neptune orbit radius 2.795 billion miles 30AU, .0005ly or 4hr20min × c
Neptune radius 15299 miles 3.85 Earth radii or .035 solar radius (3.5%)
Neptune mass 1026 kg 17 Earth masses or .00005 solar mass (0.005%)
Alpha Centauri distance 4.367 ly 9200 × Neptune's orbit radius
Galactic Center distance 26000 ly 6000 × distance to Alpha Centauri
Milky Way number of stars 100-400 billion
Milky Way visible diameter 100,000 ly 30kpc
Milky Way visible depth 10,000 ly 3kpc
Milky Way Galactic Halo diameter 300,000-400,000 ly 100kpc
Canis Major Dwarf Galaxy distance (claimed nearest Galaxy) 25000 ly 8kpc
Sagittarius Dwarf Elliptical Galaxy (Sgr dE) (accepted nearest galaxy) 81000 ly 25kpc
Andromeda (M31) distance (nearest similar galaxy) 2.537 million ly 778kpc, .8Mpc or 25 Milky Way diameters
Local Group (LG) diameter 10Mly 3Mpc or 100 Milky Way diameters
Local Group galaxy count 54
Virgo cluster (nearest Galaxy Cluster (CL)) distance 59Mly 18Mpc
Virgo cluster galaxy count 1000-2000
Virgo Supercluster diameter 110Mly 34Mpc
Virgo Supercluster cluster/group count 100
Virgo supercluster galaxy count 47000
Laniakea Supercluster diameter 520Mly 160Mpc or distance to z = 0.04
Laniakea cluster count 300-500
Laniakea galaxy count 100,000
typical stars per galaxy billions to 100 trillion
superclusters in observable universe estimated 10 million
galaxies in observable universe estimated 170 billion
stars in the universe estimated 1024 (septillion)
age of universe 13.82 billion years
diameter of observable universe 93Gly 28.5Gpc or 180 × Laniakea radius
mass of observable universe estimated 1053kg
Visible Light Wavelengths 4000-7000 Angstroms (Å) 4×10-7 to 7×10-7 meters
atoms in a gram of Hydrogen (H) (Avogadro's Number) 6.022×1023
atoms in the universe estimated 1078 to 1082
photons in the universe estimated 1089
Neutrino (ν) 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