Useful Units
Earth diameter = 13,000 km
Moon diameter= 3,500 km
Mean Earth-Moon distance = 380,000 km
Mean Earth-Sun (1 AU) = 150 million km
Sun diameter = 1.4 million km
Temperature of the Sun’s photosphere = 5,800 K

The Sun
Moon: First Quarter, Waxing
Moon: Full
Moon: Last Quarter, Waning
Moon: New
Earth (Alternative)


Ascending node
Descending node
δ Declination
α Right Ascension

symbol Double Star
symbol Variable Star
symbol Galaxy
symbol Globular Cluster
symbol Open Cluster
symbol Planetary Nebula
symbol Diffuse Nebula
symbol Quasar

Solar Masses
λ Wavelength
π Parallax
2 Square
3 Cube
Square Root
Cube Root
P Period

r Radius
T Time regarding Orbit
M Absolute Magnitude
m Apparent magnitude
M Messier object, e.g. M31
M Mass
v Velocity
H0 Hubble constant

D / d Declination / Distance
c Speed of light (300,000 km/s)
pc Parsec
K Kelvin
α Right Ascension
δ Declination
L Luminosity

You may find some abbreviations used on other web sites you visit. These are some of the most common.

Various Abbreviations
AU   Astronomical Unit
BAe   British Aerospace
BST   British Summer Time
CCD   Charge-Coupled Device
Dec   Declination
ESA   European Space Agency
GMT   Greenwich Mean Time
GPS   Global Positioning System
HR   Hertzsprung-Russell
HST   Hubble Space Telescope
JPL   Jet Propulsion Laboratory
KAO   Kuiper Airborne Observatory
Continued Various Abbreviations
KSC   Kennedy Space Center
LY   Light Year
M     Messier
NASA   National Aeronautics and Space Administration
RA   Right Ascension
RAS   Royal Astronomical Society
SCT   Schmidt-Cassegrain Telescope
SETI   Search for ExtraTerrestrial Intelligence
SOHO   Solar Heliospheric Observatory
UTC   Coordinated Universal Time
VLA   Very Large Array
VLT   Very Large Telescope

  • Wikipedia List of astronomy acronyms
  • Glen Petitpas Dumb Or Overly Forced Astronomical Acronyms Site (or DOOFAAS)

List of Constellations, Abbreviations and English meaning
Constellation Abbreviations English
Andromeda AND Chained Lady
Antlia ANT Air Pump
Apus APS Bird of Paradise
Aquarius AQR Water Bearer
Aquila AQL Eagle
Ara ARA Altar
Aries ARI Ram
Auriga AUR Charioteer
Boötes BOO Herdsman
Caelum CAE Engraving Tool
Camelopardalis CAM Giraffe
Cancer CNC Crab
Canes Venatici CVN Hunting Dogs
Canis Major CMA Larger Dog
Canis Minor CMI Smaller Dog
Capricornus CAP Water Goat
Carina CAR Keel
Cassiopeia CAS Queen
Centaurus CEN Centaur
Cepheus CEP King
Cetus CET Whale/Sea Monster
Chamaeleon CHA Chameleon
Circinus CIR Compasses
Columba COL Dove
Coma Berenices COM Berenices Hair
Corona Australis CRA Southern Crown
Corona Borealis CRB Northern Crown
Corvus CRV Crow, Raven
Crater CRT Cup
Crux CRU Southern Cross
Cygnus CYG Swan
Delphinus DEL Dolphin
Dorado DOR Swordfish
Draco DRA Dragon
Equuleus EQL Little Horse
Eridanus ERI River
Fornax FOR Furnace
Gemini GEM Twins
Grus GRU Crane
Hercules HER Hero; Hercules
Horologium HOR Clock
Hydra HYA Water Serpent
Hydrus HYI Water Snake
Indus IND Indian
Continued list of Constellations
Constellation Abbreviations English
Lacerta LAC Lizard
Leo LEO Lion
Leo Minor LMI Smaller Lion
Lepus LEP Hare
Libra LIB Scales
Lupus LUP Wolf
Lynx LYN Lynx
Lyra LYR Lyre
Mensa MEN Table
Microscopium MIC Microscope
Monoceros MON Unicorn
Musca MUS Fly
Norma NOR Square
Octans OCT Octant
Ophiuchus OPH Serpent Bearer
Orion ORI Hunter; Orion
Pavo PAV Peacock
Pegasus PEG Winged Horse
Perseus PER Perseus the Hero
Phoenix PHE Phoenix
Pictor PIC Easel
Pisces PSC Fishes
Piscis Austrinus PSA Southern Fish
Puppis PUP Stern
Pyxis PYX Compass
Reticulum RET Net
Sagitta SGE Arrow
Sagittarius SGR Archer
Scorpius SCO Scorpion
Sculptor SCL Sculptor
Scutum SCT Shield
Serpens SER Serpent
Sextans SEX Sextant
Taurus TAU Bull
Telescopium TEL Telescope
Triangulum TRI Triangle
Triangulum Australe TRA Southern Triangle
Tucana TUC Toucan
Ursa Major UMA Greater Bear
Ursa Minor UMI Smaller Bear
Vela VEL Sails
Virgo VIR Maiden
Volans VOL Flying Fish
Vulpecula VUL Fox

α Alpha
β Beta
γ Gamma
δ Delta
ε Epsilon
ζ Zeta

η Eta
θ Theta
ι Iota
κ Kappa
λ Lambda
μ Mu

ν Nu
ξ Xi
ο Omicron
π Pi
ρ Rho
σ Sigma

τ Tau
υ Upsilon
φ Phi
χ Chi
ψ Psi
ω Omega

. Degree

  • arc minute = 1/60th of a degree
  • arc second = 1/3600th of a degree
  • 15° =  1 hour
  • 1 degree =    4 minutes

Apparent = 'Real Sun time'
Mean = ' Human time'

The mean average distance from Earth to the Sun is 149,600,000 km, normally rounded to 150,000,000 km. This is called 1 Astronomical Unit, or AU, a standard number in astronomy.

The formula for working out if a star is circumpolar or not is
D >= 90° - L

D = Declination
> = = Greater than or equal to
L = Latitude

Right Ascension: How far an object is along the celestial equator from the first point of Aries (where the Sun crosses the Celestial Equator at the Vernal Equinox)
Measured in hours (h), minutes (m) and seconds (s) and is abbreviated as RA or α.

Arcturus: RA: 14h 15m 39.7s

Declination: How far north and south an object is from the Celestial Equator measured in degrees (°), arc minutes (‘) and arc seconds (“) and is abbreviated as dec (δ).
Arcturus: Dec: +19° 10′56″

How high an object is above the horizon from 0° at the horizon to 90° at the zenith

How far an object is eastwards in° from north

  • 1 AU = 150,000,000 (1.5 x 108)
  • 1 Light Year = 9,460,000,000,000 km (9.46 x 1012)
  • 1 Parsec = 3.26 light years

N = R* x fp x ne x fl x fi x fc x L

  • N is the number of civilizations in our galaxy with which communication might be possible;
  • R* is the average rate of star formation in our galaxy
  • fp is the fraction of those stars that have planets
  • ne is the average number of planets that can potentially support life per star that has planets
  • fℓ is the fraction of the above that actually go on to develop life at some point
  • fi is the fraction of the above that actually go on to develop intelligent life
  • fc is the fraction of civilizations that develop a technology that releases detectable signs of their existence into space
  • L is the length of time such civilizations release detectable signals into space.

EOT Formulas

apparent solar time – mean solar time

Mean solar time =

apparent solar time – EOT

Apparent solar time =

Mean solar time + EOT

v = Hd

v = velocity
H = Hubble Constant
d = distance

Multiply by the square

Example: Planet A is twice as near to the Sun as Planet B. It receives four times as much light as Planet B.
2 x 2 = 4.

1. Planets move in elliptical orbits around the Sun.

2. The Sun-planet line sweeps out equal areas in equal times. Planets move faster when they are nearer the Sun (perihelion) and slower when they are further away (aphelion).

3. T2 = r3 (Approximate value)

T = Period/ Time it takes to orbit the Sun
r = mean radius from Sun in AU

Latitude: North Pole: 90°N | Equator: 0° Latitude | South Pole: 90°S
Longitude: The measurement east or west of the prime meridian:
4 minutes = 1 degree of longitude, 1 hour = 15° of longitude

Light year (l.y.) = the distance travelled by light in a vacuum in 1 year (63 240 AU)


Magnification =

  fo (Focal length of the objective element)  
fe (Focal length of the eyepiece)

Eyepiece focal length =

Objective focal length

Objective focal length =

Magnification multiply Eyepiece focal length

Resolution =

Objective diameter

M = Absolute Magnitude
m = Apparent Magnitude
d = distance in parsecs

To work out Absolute Magnitude;
M = m + 5 - 5 log d

To work out Apparent Magnitude;
m = M-5+5 log d

Magnitude/Brightness Ratios

Difference in Magnitude

Brightness Ratio











Moon Phases by Day
Day Phase
0 New Moon
7 Waxing Half Moon (1st quarter)
14 Full Moon
22 Waning Half Moon (3rd quarter)
29 New Moon

Watt (W) = Joule per second

D = Distance
π = Parallax Angle


D =


π = D/1

Parsec (pc) = the distance at which a star would have parallax of 1 second of arc (3.26 light years.)

Large or Small number can be abbreviated.

10-2 = 1/(10 x 10) = 0.01
10-1 = 1/10  = 0.1
100 = = 1      
101 = 10 = 10    
102 = 10 x 10 = 100
103 = 10 x 10 x 10 = 1000
106 = 10 x 10 x 10 x 10 x 10 x 10 = 1,000,000
M = Mega = Million
K = Kilo = Thousand

Sidereal: An object measured against the background stars
Solar: An object measured against the Sun


Speed =


Time =


Distance =

Speed x Time

Speed of light =  300,000 km/s Use 24hr clock e.g. 4pm = 16.00 hrs

  • Celsius (°C) - 0°C = 273 K
  • Kelvin (K) - 0 K = - 273°C
  • Fahrenheit = (9/5)°C + 32

λ = wavelength
v = recession velocity
c = speed of light