Download Bright versus Nearby Stars

A Comparison of the Nearest
and Brightest Stars
• The nearest stars to
the Sun are thought
to represent the true
distribution of stars
in the disk of the
Milky Way Galaxy.
• To truly understand
the Galaxy, these
stars must be
studied.
• The bright stars that
are easily visible in
the night sky are
extraordinary stars
that are very
different from the
true common stars in
the Milky Way
Galaxy.
Distance to the 100 Nearest Stars
• Excluding white
dwarfs , there are 100
stars within 24 light
years of the Sun.
• The closest star is 4.3
light years away.
• The average distance
to the nearest stars is
17 light years.
35
30
25
20
15
10
5
22
18
14
10
6
2
0
Distance, Light Years
Distances to the 269 Brightest Stars
0
3,
00
0
50
0
2,
00
0
2,
50
0
1,
00
1,
0
• The 269 brightest stars
in the sky range in
distance from 4.3 light
years to 3,400 light
years.
• The average bright
star is 381 light years
away.
50
0
100
90
80
70
60
50
40
30
20
10
0
Distance, Light Years
Absolute Magnitude vs Distance of
the 100 Nearest Stars
-10
-5
0
5
10
15
20
1
10
100
1,000
• The nearest stars
are generally much
less luminous than
the Sun.
• Their absolute
magnitudes range
from 0 to 20.
• The Sun’s absolute
magnitude
is
4.8.
10,000
Distance, Light Years
Absolute Magnitude vs Distance of
the 269 Brightest Stars
-10
-5
0
5
10
15
20
1
10
100
1,000 10,000
Distance, Light Years
• The brightest stars
are generally much
more luminous than
the Sun.
• Their absolute
magnitudes range
from -8 to 5.
• The Sun’s absolute
magnitude is 4.8.
Absolute Magnitudes of 100
Nearby Stars
25
20
15
10
5
0
• 95% of the nearest
100 stars are less
luminous than the
Sun.
• The average nearby
star has absolute
magnitude 11.5,
equivalent to .002
solar luminosities.
0
-1
-6
-2
2
6
10
14
18
Absolute Magnitudes of 269
Bright Stars
• 95% of the brightest stars
are more luminous than
the Sun.
• The average absolute
magnitude of a bright star
is –1.2, equivalent to 300
solar luminosities.
60
50
40
30
20
10
-1
0
-7
-4
-1
2
5
8
0
Hertzsprung Russell Diagram
for 100 Nearby Stars
-10
• The nearby stars
occupy the lower
luminosity long-lived
portion of the HR
diagram.
• This survey does NOT
include the numerous
white dwarf stars in the
solar neighborhood.
-5
M
0
5
10
15
20
1
2
3
4
5
6
Spectral Type
7
8
Hertzsprung Russell Diagram
of 269 Bright Stars
-10
• The bright stars
occupy the upper high
luminosity giant
region of the HR
diagram.
• They are either
-5
M
0
5
10
15
20
0
2
4
Spectral Type
6
8
– Hot main sequence
stars, or
– Cool giant stars
Spectral Types of 100 Nearby Stars
80%
• There are no O or B
stars near the Sun.
• The Sun’s spectral
type represents only
6% of the nearby
stars.
• 88% of nearby stars
are K & M spectral
types.
Number
60%
40%
20%
0%
O B A F G K M D
Spectral Types of 269 Bright Stars
100
80
60
40
20
0
O
B
A
F
G
K
M
• All spectral types are
represented in the bright
stars.
• Over 1/3 of the bright
stars are O & B types.
• Only 13% are solar-type
G stars.
• 26% of the bright stars
are K & M type.
Luminosity Class of 100 Nearby
Stars
100%
• There are no true
giant stars with in
the 25 light years
around the Sun.
• 97 % of nearby stars
are Main Sequence
dwarf stars.
75%
50%
25%
0%
I
II
III
IV
IV-V
V
Luminosity Class of 269 Bright Stars
120
100
80
60
40
20
0
I
II
III
IV
V
p
• All luminosity classes
are represented in the
bright stars.
• 73% are late-stage
giant stars or peculiar
stars.
• Only 27% of the
bright stars are main
sequence dwarf stars.
The Average Nearby Star
• The 100 nearest stars are:
– 17 light years away on average
• Min distance = 4.3 light years
–
–
–
–
–
–
Average apparent magnitude = 10
Invisible to naked eye
88% are cool main sequence K or M Stars.
Average absolute magnitude = 11.5
Luminosity = 0.002 solar luminosities.
Very long lived stars
The Average Bright Star
• The 269 Brightest stars are:
– 381 light years away on average
• Max Distance = 3400 light years
– 75% are late stage giant stars
– 25% are young hot (most probably B) stars.
– Average absolute magnitude = -1.2
– Average luminosity = 300 solar luminosities.
– Short lived stars or stars near the of their
evolution.
• The 269 Brightest stars • The 100 nearest stars
– 381 light years away on
average
– 17 light years away on
average
• Max Distance = 3400 light
years
• Min distance = 4.3 light
years
– 75% are late stage giant
stars
– 25% are hot (most
probably B) stars.
– Average absolute
magnitude = -1.2
– Average luminosity = 640
solar luminosities.
– Short lived stars or giant
stars near the of their
evolution.
– Average apparent
magnitude = 10
– Invisible to naked eye
– 88% are cool main
sequence K or M Stars.
– Average absolute
magnitude = 11.5
– Luminosity = 0.002
solar luminosities.
– Very long lived stars