List of common astronomy symbols explained

This is a compilation of symbols commonly used in astronomy, particularly professional astronomy.

Age (stellar)

τ - age

Astrometry parameters

R_v - radial velocity
cz - apparent radial velocity
z - Redshift
μ - proper motion
π - parallax
J - epoch
α - Right Ascension
δ - Declination
λ - Ecliptic longitude
β - Ecliptic latitude
l - Galactic longitude
b - Galactic latitude

Cosmological parameters

h - dimensionless Hubble parameter
H₀ - Hubble constant
Λ - cosmological constant
Ω - density parameter
ρ - density
ρ_c - critical density
z - redshift

Distance description

Distance description for orbital and non-orbital parameters:

d - distance
- d - in km = kilometer
- d - in mi = mile
- d - in AU = astronomical unit
- d - in ly = light-year
- d - in pc = parsec
- d - in kpc = kiloparsec (1000 pc)
D_L - luminosity distance, obtaining an objects distance using only visual aspects

Galaxy comparison

Galaxy type and spectral comparison:

see galaxy morphological classification

Luminosity comparison

Luminosity comparison:

L_S, - luminosity of the Sun

Luminosity of certain object:

L_acc - accretion luminosity
L_bol - bolometric luminosity

Mass comparison

Mass comparison:

M_E, - mass of Earth
, - mass of Jupiter

Mass of certain object:

M_●^[1] - mass of black hole
M_acc - mass of accretion disc

Metallicity comparison

Metallicity comparison:

[Fe/H] - Ratio of Iron to Hydrogen. This is not an exact ratio, but rather a logarithmic representation of the ratio of a star's iron abundance compared to that of the Sun.
- for a given star (﹡) : $[\ce{Fe/H}] = \log[\ce{Fe/H}]_* - \log[\ce{Fe/H}]_\odot$ , where the values represent the number densities of the given element.
[M/H] - Metallicity ratio.
Z - Metallicity
Z_☉, Z_S - Metallicity of the Sun

Orbital parameters

Orbital Parameters of a Cosmic Object:

α - RA, right ascension, if the Greek letter does not appear, á letter will appear.
δ - Dec, declination, if the Greek letter does not appear, ä letter will appear.
P or P_orb or T - orbital period
a - semi-major axis
b - semi-minor axis
q - periapsis, the minimum distance
Q - apoapsis, the maximum distance
e - eccentricity
i - inclination
Ω - longitude of ascending node
ω - argument of periapsis
R_L - Roche lobe
M - Mean anomaly
M_o - Mean anomaly at epoch

Radius comparison

Radius comparison:

R_E, - Radius compared to Earth
, - Radius compared to Jupiter
R_S, - Radius compared to The Sun

Spectral comparison

Spectral comparison:

see Stellar classification
m_(object) - Apparent magnitude
M_(object) - Absolute magnitude, for galaxies and stars
H_(object) - Absolute magnitude, for planets and nonstellar objects

Temperature description

Temperature description:

T_eff - Temperature Effect, usually associated with luminous object
T_max - Temperature Maximum, usually associated with non-luminous object
T_avg - Temperature Average, usually associated with non-luminous object
T_min - Temperature Minimum, usually associated with non-luminous object
K - Kelvin

Notes and References

Kuncic . Z. . Soria . R. . Hung . C. K. . Freeland . M. C. . Bicknell . G. V. . August 2006 . Ultra-luminous X-ray sources: X-ray binaries in a high/hard state? . Proceedings of the International Astronomical Union . 2 . S238 . 247–250 . 10.1017/S1743921307005066 . astro-ph/0611040 . 1743-9213.