My first Magazine Sky & Telescope - 03.2019 | Page 20

Famous Stars, Part I
–15
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Hypergiants
10 6
–10
10 5
ergiants
Supe
–5
Asymptotic
giant branch
qu
en
10 3
Giants
100
10
bgiants
Sub
ce
Dwarfs
tri
s e
Brig ht giants
Red giant
branch
0
1
5
M
ai
n
.010
Subdwarfs
.001
10
10 –3
White dwarfs
10 –4
15
10 –5
Brown dwarfs
20
O
B
A
F
G
K
M
L
T
Spectral class
p LIFE OF A STAR The Hertzsprung-Russell diagram plots stars according to their spectral class (related to color and temperature) and absolute
magnitude (related to luminosity). Stars’ locations depend on their mass and age, and they move across the H-R diagram as they evolve. Stars can ex-
perience one or more unstable periods, marked by the instability strip. The black line shows the approximate path a 5-solar-mass star will take across
the diagram. When it enters the correct part of the strip, it becomes a Cepheid. (A star’s behavior in the strip depends on its mass; the fi nal crossing as
the star dies won’t create Cepheid pulsations.) The gray labels are luminosity classes (see S&T: Dec. 2018, p. 27) and their boundaries here are rough.
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M A RCH 2 019 • SK Y & TELESCOPE
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LITHOPSIAN
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