Classification of StarsHow do we classify the billions of stars that

exist in our galaxy and Universe?

How Big?

• Star - sphere of gas held together by gravity that produces tremendous amounts of energy and shines

• Creates energy by nuclear fusion

• Majority of known matter!in the galaxy

Classification of Stars

•Absolute Magnitude - how bright a star appears to an observer on Earth

• Factors that Affect Absolute Magnitude:

• Temperature

• Size

•Distance

Classification of Stars

•Absolute Brightness - the actual brightness of stars compared at a distance of 32.6 light years

• Factors that Affect Absolute Brightness:

• Temperature

• Size

Classification of Stars

• Spectral Class - classification of stars based on analyzing the electromagnetic radiation emitted

•Electromagnetic radiation is split with a prism into the rainbow of colors and spectral lines

Classification of Stars

Spectral Class

Spectral Class O28,000 K - 50,000 K

Spectral Class B10,000 K - 28,000 K

Spectral Class A7,500 K - 10,000 K

Spectral Class F6,000 K - 7,500 K

Spectral Class G5,000 K - 6,000 K

Spectral Class K3,500 K - 5,000 K

Spectral Class M2,500 - 3,500 K

• Luminosity - a measure of the rate of energy output

•Our Sun is the baseline with 1 energy unit

•Graphed on a logarithmic [non-linear] scale

Classification of Stars

• Logarithmic [non-linear] Scale:

Classification of Stars

•H-R Diagram - chart used to describe the relationship between a star’s surface temperature and luminosity

•Developed by Ejner Hertzsprung of Denmark and Henry N. Russell of the United States

Classification of Stars

H-R Diagram

Earth Science Reference Tables

(Name in italics refers to star represented by a .)

(Stages indicate the general sequence of star development.)

Color

Surface Temperature (K)

0.0001

0.001

0.01

0.1

1

10

100

1,000

10,000

100,000

1,000,000

Lu

min

osi

ty(R

ate

at w

hich

a s

tar

emits

ene

rgy

rela

tive

to th

e S

un)

20,000 10,000 8,000 6,000 4,000 3,000

Blue Blue White White Yellow

2,000

RedOrange

Sirius

Spica

Polaris

Rigel

Deneb Betelgeuse

SUPERGIANTS(Intermediate stage)

(Intermediate stage)GIANTS

Barnard’sStar

ProximaCentauri

Pollux

Alpha Centauri

Aldebaran

Sun

Procyon B SmallStars

MassiveStars

WHITE DWARFS(Late stage)

MAIN SEQUENCE

(Early stage)

40 Eridani B

30,000