Star 1st magnitude

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Since ancient Greece, the 20 brightest fixed stars have been referred to as 1st magnitude stars . In the brightness scale strictly defined by Pogson in 1850, all stars that are brighter than +1.5  mag are counted as the first size today.

There are 22 1st magnitude stars in the entire starry sky , 10 of which are north of the celestial equator and 12 are south of it. Particularly noticeable among them are four groups of stars :


The star brightness scale was introduced into astronomy by Hipparcos (190-120 BC) . He defined the weakest stars visible to the naked eye as 6th magnitude stars .

Stars that are slightly fainter than the brightest were called 2nd magnitude stars by the Greek astronomers Hipparchus (190–125 BC) and Ptolemy (100–175 AD) (e.g. Big Dipper , Cassiopeia and Orion Belt ).

Apparent brightness scale

This classification have the astronomers of modern times, a defined physically accurate logarithmic scale adapted to them as apparent brightness designate (or "magnitude" or Magnitudo, abbreviated like ):

Size class Magnitude number annotation
1. size <1.5 mag 0022nd the brightest two actually have "−1st size" (−1.5 to −0.5 mag),
the eight following "0. Size "(−0.5 to +0.5 mag)
2. size 1.5 to 2.5 mag 0070
3rd size 2.5 to 3.5 mag 0170
4. size 3.5 to 4.5 mag 0430 to Argelander / Kapteyn
5. size 4.5 to 5.5 mag 1200
6. size 5.5 to 6.5 mag 4000

This scale is designed so that each level corresponds to an intensity ratio of the light of , and therefore 5 levels exactly 1: 100. A first magnitude star is 100 times as bright as a 6th magnitude point of light, but this appears to the eye as fewer steps. The reason for this is the Weber-Fechner law of our visual sense , which on the other hand enables us to perceive differences in brightness between day and night of 1:10 billion.

The number of stars increases by a factor of 2½ to 3 per size class (cf. population index for meteor streams ), which continues for several brightness levels and is related to the visibility of distant stars in the Milky Way . Only between magnitude 14 and 18 does the factor drop to 2.3 per level, from which the total number of stars has been extrapolated to at least 30 billion .

See also