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Star Magnitude
Brightness: stars are assigned a number starting with the brightest star starting at about -1
magnitude. Dimmer stars are zero or positive numbers. The larger the number means the
dimmer the star is. For example, a star -1 magnitude is brighter than a star 0 magnitude.
A star 0 magnitude is brighter than a star 1 magnitude. A star 1 magnitude is brighter than
a star 2 magnitude. A star 4 magnitude is brighter than a star 5 magnitude. Magnitude
sequence for stars starting with the brightest is -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 magnitude,
... etc.
The First Magnitude Stars Table lists the brightest stars in the sky that are -1, 0 and 1
magnitude. Sirius is the brightest at -1.44 magnitude. These stars are referred to as First
Magnitude stars since they are all 1 magnitude or brighter.
Brightness of stars is assigned a number starting with the brightest star Sirius starting at 1.44 magnitude. Dimmer stars are positive numbers. The larger the number means the
dimmer the star is. For example, a star -1 magnitude is brighter than a star 0 magnitude.
A star 0 magnitude is brighter than a star 1 magnitude. A star 1 magnitude is brighter than
a star 2 magnitude. Magnitude sequence for stars starting with the brightest is -1, 0, 1, 2,
3, 4, 5, 6, 7, 8, 9, 10 magnitude, ... etc.
Star names come from Greek, Latin and Arabic origins. For example, Sirius and Capella
are of Greek and Latin origins and Vega, Rigel, Aldebaran are Arabic derivations. In
some cases two names are given to a star because some stars are referred to with multiple
names.
The designation column gives the star's designation by Johann Bayer's letter and John
Flamsteed's number.
Johann Bayer's Uranometer star maps (1603) introduced the designating the brighter stars
of each constellation by small letters of the Greek alphabet.
In general, the stars are lettered in order of brightness. In a constellation the brightest star
is Alpha, the second brightest Beta and so on. That is why most of the First Magnitude
Stars are designated Alpha and a few are designated Beta. The full name of the star in the
Johann Bayer system is the letter followed by the genitive (possessive) of the Latin name
of the constellation. For example, Sirius is Alpha Canis Majoris. The below table uses the
constellation abbreviations. Therefore, Sirius designation is Alpha CMa.
A different plan used in John Flamsteed's Historia Coelestis (1729). The stars are
numbered consecutively from west to east across the constellation. Therefore, in the John
Flamsteed system Sirius is designated 9 Canis Majoris.
In the Magnitude column the letter "c" refers to the combined magnitude of a double star
and "v" refers to the median magnitude of a variable star. Star magnitude data is from the
Hipparcos Catalog:
First Magnitude Stars Table
Name
Designation
Magnitude
Sirius
9 Alpha CMa
-1.44
Canopus
Alpha Car
-0.62
Rigil Kent or Alpha Centauri Alpha Cen
-0.28c
Acturus
16 Alpha Boo
-0.05v
Vega
3 Alpha Lyr
0.03v
Capella
13 Alpha Aur
0.08v
Rigel
19 Beta Ori
0.18v
Procyon
10 Alpha CMi 0.40
Achernar
Alpha Eri
0.45v
Betelgeuse or Betelgeux
58 Alpha Ori
0.45v
Agena or Hadar
Beta Cen
0.61v
Altair
53 Alpha Aql
0.76v
Acrux
Alpha Cru
0.77c
Aldebaran
87 Alpha Tau
0.87
Spica
67 Alpha Vir
0.98v
Antares
21 Alpha Sco
1.06v
Pollux
78 Beta Gem
1.16
Fomalhaut
24 Alpha PsA
1.17
Beta Crucis
Beta Cru
1.25v
Deneb
50 Alpha Cyg
1.25v
Regulus
32 Alpha Leo
1.36
The decimal point is not used when star magnitudes are used on a star map. The decimal
point could be confused for a star on the map. At the top of this page is the constellation
Ursa Minor with star magnitudes for some of its stars. For example, magnitude 31 on the
star map mean 3.1 and magnitude 55 on the star map mean 5.5.
Historically the magnitude system started with Hipparcos and Ptolemy when they divided
the stars into six magnitudes. About 20 of the brightest stars that they could observe from
their location were assigned to the first magnitude. The next set of bright stars were
assigned to second magnitude and so forth. Sixth magnitude stars were assigned to stars
that were barely visible to the unaided eye under favorable conditions. It was empirically
determined that the ratio of first magnitude to sixth magnitude was 100 to 1. A
logarithmic scale of 2.512 between magnitude levels is implemented. For example, a first
magnitude star is 100 brighter than a sixth magnitude star or the sixth magnitude star is
1/100 or .01 dimmer that a first magnitude star. Second example, a fifth magnitude star is
2.512 times brighter than a sixth magnitude star or the sixth magnitude star is 1/2.512 or
.40 dimmer that a fifth magnitude star. General rule, a star is 2.512 times brighter than a
star one magnitude less.
Six Star Magnitude Table
Logarithmic scale of
How Much Brighter
Star Magnitude
2.512 X between magnitude levels
than a Sixth Magnitude Star
Starting at Sixth Magnitude
1
100 Times
2.51 x 2.51 x 2.51 x 2.51 x 2.51
2
39.8 Times
2.51 x 2.51 x 2.51 x 2.51
3
15.8 Times
2.51 x 2.51 x 2.51
4
6.3 Times
2.51 x 2.51
5
2.51 Times
2.51 x
6
With the invention of the telescope and modern equipment to measure star magnitudes
the scale has been extended in both directions. Dimmer stars are assigned magnitudes
larger than 6 ( 6, 7, 8, 9, ... 30th ... etc.) The Hubble Space Telescope Deep Field image
contains some galaxies as faint as 30th magnitude. First magnitude stars are corrected
across the scale of 1, 0, -1 with the brightest star Sirius at -1.44. The scale increases in
brightness with negative numbers. For example, the brightest planet Venus varies in
brightness and is about -4.4 magnitude at maximum brightness. The Moon is -12.7
magnitude at maximum brightness and the Sun is -26.75 magnitude.
The below Star Magnitude Table Based on -1 Magnitude Star shows how much dimmer
than a -1 magnitude star are stars to 19th magnitude. For example, most 10 x 50 or 7 x 50
binoculars can detect a 9 magnitude star. A 9 magnitude star is one tenth thousand
(1/10,000 or .0001) dimmer than -1 magnitude star.
Star Magnitude Table Showing How Much Dimmer other Magnitudes are as Compared
to a -1 Magnitude Star
Star Magnitude
How Much Dimmer
How Much Dimmer
than a -1 Magnitude Star than a -1 Magnitude Star
-1
0
1/2.51
0.398
1
1/6.31
0.158
2
1/15
0.063
3
1/39
0.0251
4
1/100
0.0100
5
1/251
0.00398
6
1/630
0.00158
7
1/1,584
0.000630
8
1/3,981
0.000251
9
1/10,000
0.000100
10
1/25,118
0.0000398
11
1/63,095
0.0000158
12
1/158,489
0.00000631
13
1/398,107
0.00000251
14
1/1,000,000
0.00000100
15
1/2,511,886
0.000000398
16
1/6,309,573
0.000000158
17
1/15,848,931
0.000000063
18
1/39,810,717
0.000000025
19
1/100,000,000
0.000000010
The stars in Ursa Minor are a good constellation to determine how faint of a star can be
observed. On star maps bright stars are represented with large dots while dimmer stars
are represented with smaller dots. The brightness of the stars of Ursa Minor get fainter
starting with Polaris at 2.0 magnitude which is located on the right side of the below star
maps. The rest of the stars starting from bright to dim are 2.1, 3.1, 4.2, 4.3, 4.4, 5.0, 5.2
and 5.5 magnitude. Also note that Polaris is located in the same place in the sky
throughout the year for each observing location.