Limiting magnitude

Limiting magnitude is used to evaluate the quality of observing conditions. It tells the magnitude of the faintest star visible by naked eye. The limiting magnitude could also be observed by some instrument. It describes well the transparency. As fainter stars are visible, as better the transparency is.

Limiting magnitude is used eg. in meteor and deep sky observations. It can be used also to approximate light pollution.

Other limiting magnitude web pages:

• Estimating Limiting Magnitude, (Bill Arnett)
• Determination of the limiting magnitude, (International Meteor Organisation)

Estimation of limiting magnitude

The simplest way to evaluate limiting magnitude is to find suitable stars with known magnitudes from star map and check which of them are visible. More clever way is to calculate visible stars inside known star squares and tringles including the corner stars. This method is originally invented by meteor observers.

The areas used in limiting magnitude estimation

Area   Corner stars                     Constellation

  1    Chi-Zeta-Delta-Xi Dra            Draco
  2    Beta-Delta-Zeta Per              Perseus
  3    23-Theta-Beta UMa                Ursa Major
  4    Alpha-Epsilon-Beta Gem           Gemini
  5    Tseta-Gamma-Delta Aql            Aquila
  6    Alpha And - Gamma-Alpha Peg      Pegasus-Andromeda
  7    Alpha-Beta-Delta Cep             Cepheus
  8    Alpha-Beta-Zeta Tau              Taurus
  9    Alpha-Beta-Gamma-Delta Leo       Leo
 10    Alpha-Zeta-Gamma Vir             Virgo
 11    Alpha CrB - Gamma-Alpha Boo      Corona Borealis-Bootes
 12    Alpha Ser - Beta Lib - Delta Oph Serpens-Libra-Ophiuchus
 13    Beta-Zeta Lyr - Theta-Nu Her     Lyra-Hercules
 14    Epsilon-Eta-Gamma Cyg            Cygnus
 15    Beta Dra - Tau-Pi Her            Draco-Hercules
 16    Alpha CVn - Epsilon-Eta UMa      Canes Venatici-Ursa Major
 17    Epsilon-Theta-Delta Aur          Auriga
 18    Mu-Gamma-Phi And                 Andromeda
 19    Kappa-Alpha Dra - Beta UMi       Draco-Ursa Minor
 20    42-Beta-Gamma Cam                Camelopardalis

In observations the area should choose so, that it is either near the view direction or zenith, depending on observations and the situation. Meteor observers use the viewing direction. Deep sky observers (In Finland) use the area in 45 degrees altitude.

These pages are maintained by:
Veikko Mäkelä, Veikko.Makela@ursa.fi
Mika Pirttivaara, Mika.Pirttivaara@ursa.fi