Astronomical Data
Planetary, stellar, galactic, and cosmological data — from Solar System body properties to the Hubble constant — with current best-known uncertainties.
Source: IAU 2022; Planck 2018; NASA JPL Horizons
Astronomical Constants & Units
Speed of light c
| Value | 299 792 458 | m s⁻¹ | exact |
Gravitational constant G
| Value | 6.674 30 × 10⁻¹¹ ± 0.000 15 × 10⁻¹¹ | m³ kg⁻¹ s⁻² |
Astronomical Unit AU
| Value | 1.495 978 707 × 10¹¹ | m | exact |
| Value (in km) | 149 597 870.700 | km | exact |
Parsec pc
| Value | 3.085 677 581 491 × 10¹⁶ | m | |
| Value (in ly) | 3.261 563 777 | ly |
Light year ly
| Value | 9.460 730 472 580 8 × 10¹⁵ | m | exact |
| Value (in AU) | 63 241.077 | AU |
Solar mass M☉
| Value | 1.988 416 × 10³⁰ ± 0.000 006 × 10³⁰ | kg | |
| GM☉ (heliocentric gravitational constant) | 1.327 124 400 18 × 10²⁰ ± 0.000 000 000 99 × 10²⁰ | m³ s⁻² |
Solar radius R☉
| Value (IAU 2015 nominal) | 6.957 × 10⁸ | m | exact |
Solar luminosity L☉
| Value (IAU 2015 nominal) | 3.828 × 10²⁶ | W | exact |
Earth mass M⊕
| Value | 5.972 17 × 10²⁴ ± 0.000 13 × 10²⁴ | kg | |
| GM⊕ (geocentric gravitational constant) | 3.986 004 418 × 10¹⁴ ± 0.000 000 008 × 10¹⁴ | m³ s⁻² |
Earth equatorial radius R⊕
| Value (GRS80) | 6 378 137 | m | exact |
Julian year
| Value | 365.25 | days = 31 557 600 s | exact |
Tropical year (2000)
| Value | 365.242 189 6 | days |
Sidereal year
| Value | 365.256 363 004 | days |
The Sun
Mass M☉
| Value | 1.988 416 × 10³⁰ ± 0.000 006 × 10³⁰ | kg |
Equatorial radius R☉
| Value | 6.957 × 10⁸ | m (695 700 km) | exact |
Luminosity L☉
| Value | 3.828 × 10²⁶ | W | exact |
Effective surface temperature T☉
| Value | 5 778 ± 3 | K |
Central temperature Tc
| Value | 1.571 × 10⁷ | K |
Central density ρc
| Value | 1.622 × 10⁵ | kg m⁻³ |
Central pressure Pc
| Value | 2.477 × 10¹⁶ | Pa |
Mean density
| Value | 1 408 | kg m⁻³ |
Surface gravity g☉
| Value | 274.0 | m s⁻² |
Escape velocity
| Value | 617.7 | km s⁻¹ |
Sidereal rotation period (equator)
| Value | 25.38 | days |
Sidereal rotation period (poles)
| Value (differential rotation) | ~36 | days |
Spectral type
| Value | G2V |
Absolute visual magnitude MV
| Value | +4.83 |
Apparent visual magnitude
| Value | −26.74 ± 0.01 |
Age
| Value | 4.603 × 10⁹ ± 0.005 × 10⁹ | yr |
Distance to galactic center R₀
| Value | 8.178 ± 0.022 | kpc |
Solar wind speed (at 1 AU)
| Typical value | 400–700 | km s⁻¹ |
Solar irradiance at 1 AU (solar constant)
| Value | 1 361.0 ± 0.5 | W m⁻² |
Solar oblateness (J₂)
| Value | (2.1826 ± 0.0050) × 10⁻⁷ |
Composition (fraction by mass)
| Hydrogen X | 0.7381 ± 0.0030 | ||
| Helium Y | 0.2485 ± 0.0035 |
Planets & Earth's Moon
Mercury
| Mass | 3.301 1 × 10²³ | kg (0.0553 M⊕) | |
| Mean radius | 2 439.7 ± 1.0 | km | |
| Semi-major axis | 0.387 098 | AU | |
| Orbital period | 87.969 | days | |
| Orbital eccentricity | 0.205 630 | ||
| Orbital inclination | 7.005 | ° | |
| Surface gravity | 3.70 | m s⁻² | |
| Escape velocity | 4.25 | km s⁻¹ |
Venus
| Mass | 4.8675 × 10²⁴ | kg (0.815 M⊕) | |
| Mean radius | 6 051.8 ± 1.0 | km | |
| Semi-major axis | 0.723 332 | AU | |
| Orbital period | 224.701 | days | |
| Orbital eccentricity | 0.006 772 | ||
| Surface gravity | 8.87 | m s⁻² | |
| Escape velocity | 10.36 | km s⁻¹ | |
| Surface temperature (mean) | 737 | K (464 °C) |
Earth
| Mass M⊕ | 5.972 17 × 10²⁴ ± 0.000 13 × 10²⁴ | kg | |
| Equatorial radius | 6 378.137 | km | exact |
| Polar radius | 6 356.752 | km | |
| Flattening f | 1/298.257 223 563 | exact | |
| Semi-major axis | 1.000 001 018 | AU | |
| Sidereal orbital period | 365.256 363 004 | days | |
| Orbital eccentricity | 0.016 708 634 | ||
| Orbital inclination (to ecliptic) | 0.000 | ° (reference plane) | exact |
| Axial tilt (obliquity, J2000) | 23.439 291 1 | ° | |
| Equatorial surface gravity g | 9.780 327 | m s⁻² | |
| Standard gravity gn | 9.806 65 | m s⁻² | exact |
| Escape velocity | 11.186 | km s⁻¹ | |
| Mean density | 5 514 | kg m⁻³ | |
| Sidereal rotation period | 23 h 56 min 4.091 s | ||
| J₂ (second zonal harmonic) | 1.082 626 × 10⁻³ |
Moon
| Mass | 7.342 × 10²² ± 0.001 × 10²² | kg (0.0123 M⊕) | |
| Mean radius | 1 737.4 ± 1.0 | km | |
| Semi-major axis (from Earth) | 384 400 | km | |
| Sidereal orbital period | 27.321 661 | days | |
| Synodic period (lunar month) | 29.530 589 | days | |
| Orbital eccentricity | 0.054 9 | ||
| Surface gravity | 1.620 | m s⁻² | |
| Escape velocity | 2.38 | km s⁻¹ | |
| Mean density | 3 346 | kg m⁻³ |
Mars
| Mass | 6.4171 × 10²³ | kg (0.107 M⊕) | |
| Mean radius | 3 389.5 ± 0.2 | km | |
| Semi-major axis | 1.523 679 | AU | |
| Orbital period | 686.971 | days | |
| Orbital eccentricity | 0.093 400 | ||
| Surface gravity | 3.721 | m s⁻² | |
| Escape velocity | 5.03 | km s⁻¹ | |
| Axial tilt | 25.19 | ° | |
| Sidereal day | 24 h 37 min 22.7 s |
Jupiter
| Mass | 1.898 19 × 10²⁷ ± 0.000 02 × 10²⁷ | kg (317.8 M⊕) | |
| Equatorial radius | 71 492 ± 4 | km (11.21 R⊕) | |
| Polar radius | 66 854 | km | |
| Semi-major axis | 5.202 887 | AU | |
| Orbital period | 11.862 | yr | |
| Orbital eccentricity | 0.048 775 | ||
| Equatorial surface gravity | 24.79 | m s⁻² | |
| Escape velocity | 59.5 | km s⁻¹ | |
| Rotation period (equatorial) | 9 h 50 min 30 s | ||
| Number of known moons | 95 | (as of 2023) |
Saturn
| Mass | 5.683 4 × 10²⁶ | kg (95.2 M⊕) | |
| Equatorial radius | 60 268 ± 4 | km (9.45 R⊕) | |
| Semi-major axis | 9.537 070 | AU | |
| Orbital period | 29.457 | yr | |
| Orbital eccentricity | 0.055 723 | ||
| Equatorial surface gravity | 10.44 | m s⁻² | |
| Escape velocity | 35.5 | km s⁻¹ | |
| Mean density | 687 | kg m⁻³ (less than water) | |
| Ring system outer radius (A ring) | 136 800 | km |
Uranus
| Mass | 8.681 × 10²⁵ | kg (14.54 M⊕) | |
| Equatorial radius | 25 559 ± 4 | km (4.01 R⊕) | |
| Semi-major axis | 19.189 165 | AU | |
| Orbital period | 84.011 | yr | |
| Orbital eccentricity | 0.047 168 | ||
| Surface gravity | 8.87 | m s⁻² | |
| Axial tilt | 97.77 | ° (retrograde) |
Neptune
| Mass | 1.024 × 10²⁶ | kg (17.15 M⊕) | |
| Equatorial radius | 24 764 ± 15 | km (3.88 R⊕) | |
| Semi-major axis | 30.069 963 | AU | |
| Orbital period | 164.800 | yr | |
| Orbital eccentricity | 0.008 586 | ||
| Surface gravity | 11.15 | m s⁻² | |
| Escape velocity | 23.5 | km s⁻¹ |
Dwarf Planets & Selected Moons
Pluto (dwarf planet)
| Mass | 1.303 × 10²² ± 0.003 × 10²² | kg | |
| Mean radius | 1 188.3 ± 1.6 | km | |
| Semi-major axis | 39.482 | AU | |
| Orbital period | 247.94 | yr | |
| Orbital eccentricity | 0.248 8 | ||
| Surface gravity | 0.620 | m s⁻² |
Ceres (dwarf planet, largest asteroid)
| Mass | 9.384 × 10²⁰ ± 0.001 × 10²⁰ | kg | |
| Mean radius | 476.2 ± 1.7 | km | |
| Semi-major axis | 2.767 | AU |
Eris (dwarf planet)
| Mass | 1.660 × 10²² ± 0.006 × 10²² | kg (slightly > Pluto) | |
| Semi-major axis | 67.8 | AU |
Io (Jupiter I)
| Mass | 8.932 × 10²² | kg | |
| Mean radius | 1 821.6 ± 0.5 | km | |
| Orbital period | 1.769 | days | |
| Notable feature | Most volcanically active body in solar system |
Europa (Jupiter II)
| Mass | 4.800 × 10²² | kg | |
| Mean radius | 1 560.8 ± 0.5 | km | |
| Orbital period | 3.551 | days | |
| Ocean depth (estimated) | 60–150 | km |
Ganymede (Jupiter III) — largest moon
| Mass | 1.482 × 10²³ | kg (larger than Mercury) | |
| Mean radius | 2 634.1 ± 0.3 | km | |
| Orbital period | 7.155 | days |
Titan (Saturn VI) — only moon with thick atmosphere
| Mass | 1.346 × 10²³ | kg | |
| Mean radius | 2 574.7 ± 0.1 | km | |
| Orbital period | 15.945 | days | |
| Surface pressure | 1.47 × 10⁵ | Pa (1.45 atm) |
Triton (Neptune I) — retrograde orbit
| Mass | 2.14 × 10²² | kg | |
| Mean radius | 1 353.4 ± 0.9 | km | |
| Orbital period (retrograde) | 5.877 | days |
Nearby Stars & Stellar Properties
Proxima Centauri (α Cen C)
| Distance | 1.2953 ± 0.0004 | pc (4.2441 ly) | |
| Spectral type | M5.5Ve | ||
| Mass | 0.1221 ± 0.0022 | M☉ | |
| Radius | 0.1542 ± 0.0045 | R☉ | |
| Luminosity | 0.001 567 | L☉ | |
| Surface temperature | 2 992 ± 23 | K |
Alpha Centauri A (α Cen A)
| Distance | 1.340 | pc (4.37 ly) | |
| Spectral type | G2V | ||
| Mass | 1.100 ± 0.006 | M☉ | |
| Radius | 1.2234 ± 0.0053 | R☉ | |
| Luminosity | 1.519 ± 0.016 | L☉ |
Alpha Centauri B (α Cen B)
| Spectral type | K1V | ||
| Mass | 0.9070 ± 0.0060 | M☉ | |
| Luminosity | 0.5002 ± 0.0007 | L☉ |
Barnard's Star
| Distance | 1.828 | pc (5.96 ly) | |
| Spectral type | M4Ve | ||
| Proper motion | 10.358 | arcsec yr⁻¹ (largest of any star) |
Sirius A (α CMa)
| Distance | 2.637 | pc (8.60 ly) | |
| Spectral type | A1V | ||
| Mass | 2.063 ± 0.023 | M☉ | |
| Radius | 1.711 ± 0.013 | R☉ | |
| Luminosity | 25.4 | L☉ | |
| Apparent visual magnitude | −1.46 | (brightest star in sky) |
Sirius B (white dwarf)
| Mass | 1.018 ± 0.011 | M☉ | |
| Radius | 0.008 4 | R☉ (~Earth-size) |
Vega (α Lyr)
| Distance | 7.68 | pc (25.0 ly) | |
| Spectral type | A0Va | ||
| Luminosity | 40.12 | L☉ | |
| Apparent visual magnitude (photometric standard) | 0.03 |
Betelgeuse (α Ori) — red supergiant
| Distance | 170 ± 40 | pc (~550 ly) | |
| Spectral type | M1-2Ia-Iab | ||
| Mass | 16.5–19 | M☉ | |
| Radius | 764–1 021 | R☉ (variable) | |
| Luminosity | 90 000–150 000 | L☉ | |
| Surface temperature | 3 500 ± 200 | K |
Chandrasekhar mass limit (white dwarf)
| Value | 1.44 | M☉ |
Tolman–Oppenheimer–Volkoff limit (neutron star)
| Value (estimated) | ~2.2–2.9 | M☉ |
Milky Way Galaxy
Morphology
| Type | Barred spiral (SBbc) |
Disk diameter (luminous)
| Value | ~50 | kpc (~160 000 ly) |
Thin disk scale height
| Value | ~300 | pc |
Thick disk scale height
| Value | ~900 | pc |
Disk scale length
| Value | ~3.5 | kpc |
Solar galactocentric distance R₀
| Value (GRAVITY Collaboration 2019) | 8.178 ± 0.022 | kpc |
Local circular velocity V₀
| Value | 240 ± 8 | km s⁻¹ |
Galactic rotation period (at R₀)
| Value | ~225 | Myr |
Stellar mass
| Value | ~6 × 10¹⁰ | M☉ |
Total mass (within ~200 kpc)
| Value | (1.06 ± 0.20) × 10¹² | M☉ |
Number of stars
| Estimate | (2–4) × 10¹¹ |
Dark matter halo virial radius
| Value | ~200 | kpc |
Galactic bar half-length
| Value | ~5 | kpc |
Galactic center black hole Sgr A*
| Mass | (4.154 ± 0.014) × 10⁶ | M☉ | |
| Schwarzschild radius | ~12.4 | million km (~0.08 AU) | |
| Distance from Earth | 8.178 ± 0.022 | kpc (26 670 ly) |
Local Group total mass
| Value | ~3 × 10¹² | M☉ |
Andromeda Galaxy (M31) distance
| Value | 0.770 ± 0.040 | Mpc (2.51 Mly) |
Andromeda Galaxy (M31) mass
| Value | ~10¹² | M☉ |
Milky Way – Andromeda merger
| Expected time | ~4.5 | Gyr from now |
Large Magellanic Cloud distance
| Value | 49.97 ± 0.19 | kpc (163 000 ly) |
Local standard of rest (LSR) velocity
| Peculiar motion of Sun | (U, V, W) = (11.1, 12.2, 7.3) | km s⁻¹ |
Cosmological Parameters (Planck 2018)
Hubble constant H₀ (Planck 2018 CMB)
| Value | 67.36 ± 0.54 | km s⁻¹ Mpc⁻¹ |
Hubble constant H₀ (SH0ES 2022, Cepheids)
| Value | 73.04 ± 1.04 | km s⁻¹ Mpc⁻¹ |
Hubble tension
| Significance | ~5σ discrepancy between early- and late-universe probes |
Hubble radius c/H₀ (Planck value)
| Value | ~4 420 | Mpc |
Age of the universe t₀
| Value (Planck 2018) | 13.797 ± 0.023 | Gyr |
Total density parameter Ω_total
| Value | 1.0007 +0.0019/−0.0019 | (spatially flat to high precision) |
Matter density Ω_m
| Value | 0.3153 ± 0.0073 |
Dark energy density Ω_Λ
| Value | 0.6847 ± 0.0073 |
Baryon density Ω_b
| Value | 0.0493 ± 0.0006 |
Baryon density Ω_b h²
| Value | 0.022 37 ± 0.000 15 |
Cold dark matter density Ω_c h²
| Value | 0.1200 ± 0.0012 |
Radiation density Ω_r
| Value | ~9.4 × 10⁻⁵ | (photons + neutrinos) |
Dark energy equation of state w
| Value (assuming cosmological constant) | −1 | exact |
Critical density ρ_c = 3H₀²/8πG
| Value (Planck H₀) | ~8.62 × 10⁻²⁷ | kg m⁻³ |
Scalar spectral index ns
| Value | 0.9649 ± 0.0042 |
Amplitude of scalar perturbations As
| Value (k₀ = 0.05 Mpc⁻¹) | 2.100 × 10⁻⁹ ± 0.030 × 10⁻⁹ |
Matter power spectrum amplitude σ₈
| Value | 0.8111 ± 0.0060 |
Optical depth to reionization τ
| Value | 0.0544 ± 0.0073 |
Redshift of reionization z_reion
| Value | 7.67 ± 0.73 |
Redshift of recombination z_rec
| Value | 1 089.92 ± 0.25 |
Redshift of matter–radiation equality z_eq
| Value | 3 402 ± 26 |
Sound horizon at recombination rs
| Value | 144.43 ± 0.26 | Mpc (BAO standard ruler) |
Comoving distance to CMB last scattering
| Value | ~14 080 | Mpc |
Observable universe comoving radius
| Value | ~14 250 | Mpc (46.5 Gly) |
Tensor-to-scalar ratio r
| Upper limit | < 0.063 | (95% CL, no primordial GWs detected) | upper bound |
Cosmic Microwave Background
CMB temperature T₀
| Value (FIRAS, Fixsen 2009) | 2.725 48 ± 0.000 57 | K | |
| Constraint (Planck 2018) | 2.725 8 ± 0.001 5 | K |
Peak wavelength (Wien law)
| Value | 1.063 | mm (microwave) |
Peak frequency
| Value | 160.2 | GHz |
CMB photon number density nγ
| Value | 411 ± 1 | cm⁻³ |
CMB energy density ργ
| Value | 4.17 × 10⁻¹⁴ | J m⁻³ |
CMB entropy density sγ
| Value | 2.89 × 10³ | cm⁻³ |
Baryon-to-photon ratio η = nb/nγ
| Value | (6.12 ± 0.04) × 10⁻¹⁰ |
CMB dipole amplitude
| Value | 3.362 1 ± 0.001 0 | mK |
CMB dipole direction
| Galactic coordinates (l, b) | (264.0°, +48.2°) |
CMB dipole (Solar System peculiar velocity)
| Speed | 369.82 ± 0.11 | km s⁻¹ |
Primary CMB anisotropy ΔT/T (rms)
| Value | ~10⁻⁵ |
First acoustic peak l₁
| Multipole moment | ~220 |
First acoustic peak amplitude
| Value | ~6 000 | μK² |
Epoch of recombination
| Redshift z_rec | 1 089.92 ± 0.25 | ||
| Age of universe at recombination | ~380 000 | yr |
Neutrino background temperature Tν
| Value (standard model) | (4/11)^(1/3) T₀ = 1.945 | K |
Effective number of relativistic species Neff
| Value (Planck 2018) | 2.99 ± 0.17 | (consistent with 3 neutrino generations) |
Gravitational Wave Events
GW150914 — first detection (LIGO, 14 Sep 2015)
| Primary mass m₁ | 35.6 +4.7/−3.1 | M☉ | |
| Secondary mass m₂ | 30.6 +3.0/−4.4 | M☉ | |
| Final black hole mass Mf | 63.1 +3.4/−3.0 | M☉ | |
| Radiated energy | 3.0 +0.5/−0.5 | M☉ c² (~5.4 × 10⁴⁷ J) | |
| Luminosity distance DL | 440 +160/−180 | Mpc | |
| Peak strain h | ~1 × 10⁻²¹ | ||
| Peak GW frequency | ~150 | Hz |
GW170817 — first BNS merger (LIGO + Virgo, 17 Aug 2017)
| Total mass M_total | 2.74 +0.04/−0.01 | M☉ | |
| Chirp mass Mc | 1.186 +0.001/−0.001 | M☉ | |
| Luminosity distance DL | 40 +8/−14 | Mpc (host: NGC 4993) | |
| Speed of gravity c_GW/c − 1 | (−3 to +7) × 10⁻¹⁶ | (GW arrived 1.74 s before γ-ray) | |
| Hubble constant H₀ (standard siren) | 70 +12/−8 | km s⁻¹ Mpc⁻¹ | |
| Kilonova counterpart | AT2017gfo — confirmed r-process nucleosynthesis |
GW190521 — intermediate-mass BH (21 May 2019)
| Total mass | 150 +29/−17 | M☉ | |
| Final BH mass Mf | 142 +28/−16 | M☉ (intermediate mass black hole) | |
| Luminosity distance DL | 5.3 +2.4/−2.6 | Gpc |
GW event statistics (O1+O2+O3)
| Total confident detections | ~90 | events | |
| Binary black hole (BBH) mergers | ~80 | ||
| Binary neutron star (BNS) mergers | 2 | ||
| NS–BH mergers | 2 (GW200105, GW200115) |
LIGO design strain sensitivity
| Value (at ~100 Hz) | ~10⁻²³ | Hz⁻¹/² |
Large-Scale Structure & Cosmological Distances
Hubble radius (c/H₀)
| Value (Planck H₀ = 67.36) | 4 420 | Mpc (14.4 Gly) |
Particle horizon (observable universe radius)
| Value | 14 250 | Mpc (46.5 Gly) |
Comoving distance to z = 1
| Value | 3 396 | Mpc |
Comoving distance to z = 6 (high-z galaxies)
| Value | 8 860 | Mpc |
Luminosity distance to z = 1
| Value | 6 792 | Mpc |
Critical density ρ_c (present-day, Planck H₀)
| Value | 8.62 × 10⁻²⁷ | kg m⁻³ |
Critical density ρ_c (present-day)
| In M☉ Mpc⁻³ | 1.26 × 10¹¹ | M☉ Mpc⁻³ |
Mean matter density ρ_m (present-day)
| Value | ~2.7 × 10⁻²⁷ | kg m⁻³ |
Large-scale structure — BAO scale
| Value (comoving) | ~150 | Mpc |
Large-scale structure — typical galaxy cluster mass
| Value | 10¹⁴–10¹⁵ | M☉ |
Large-scale structure — cosmic web filament length
| Typical scale | 50–100 | Mpc |
Supercluster scale (Laniakea)
| Diameter | ~160 | Mpc (520 Mly) | |
| Mass | ~10¹⁷ | M☉ |
Cosmic void typical diameter
| Value | ~30–300 | Mpc |
Epoch of matter–energy equality
| Redshift z_eq | 3 402 ± 26 | ||
| Age of universe | ~50 000 | yr |
Epoch of dark energy domination onset
| Redshift | ~0.4 |
Deceleration parameter q₀
| Value (ΛCDM) | −0.527 | (universe accelerating) |