Post on 13-Oct-2020
Star Classification Notes
Daily Objective:Students will be
able to classify stars by
completing the Hertz sprung
Russell Diagram
A. The sun’s composition can be
determined from an absorption spectra.
B. The dark lines are spectral lines caused
by different chemical elements that absorb
light at specific wavelengths.
C. Scientists compare emission spectra of
different known gases, with the absorption
spectra of the Sun to identify the sun’s
elements.
D. Other stars also have dark absorption
lines in their spectra, and are classified
according to their patterns of absorption
lines.
E. Stars are assigned spectral types in
the following order: O, B, A, F, G, K, and
M.
•O being the hottest (50,000 K)
and
•M being the coolest (2000 K).
Spectral
Class
Intrinsic
Color
Temperature
(K) Prominent Absorption Lines
O Blue 41,000 He+, O++, N++, Si++, He, H
B Blue 31,000 He, H, O+, C+, N+, Si+
A Blue-white 9,500 H(strongest), Ca+, Mg+, Fe+
F White 7,240 H(weaker), Ca+, ionized metals
G Yellow-white 5,920 H(weaker), Ca+, ionized & neutral metal
K Orange 5,300 Ca+(strongest), neutral metals strong,
H(weak)
M Red 3,850 Strong neutral atoms, TiO
F. Hotter stars have simple spectra, while
cooler stars have spectra with more lines.
•Coolest stars have
more bands in their
spectra due to
molecules such as
titanium oxide, in their
atmosphere.
•Typically, about 73 %
of a star’s mass is
Hydrogen, about 25%
is helium, and the
remaining 2% varies in
composition.
Astronomers use 4 categories
to classify stars.
1. APPARENT MAGNITUDE The
brightness of a star as it appears to us on
Earth. DOES NOT take distance into
account.
2. ABSOLUTE MAGNITUDE
How bright the star would appear at a
distance of 10 parsecs. The brighter the
star, the lower the absolute magnitude.
MORE ACCURATE
3. LUMINOSITYTotal energy
output.
4. Surface Temperature
The temperature on the surface of the
observed star.
Astronomers mainly use surface
temperature and luminosity to
classify stars.
Star Classification:
•The properties of mass, luminosity,
temperature, and diameter are closely
related.
•Each class of star has a specific mass,
luminosity, magnitude, temperature, and
diameter.
•These relationships can be demonstrated on a graph
called the Hertzsprung Russell (HR) Diagram.
RED
+
BRIGHT
DIM
HIGH
ENERGY
LOW
ENERGY
•Absolute Magnitude and luminosity are
plotted on the y-axis and temperature (or
spectral class) plotted on the x-axis.
RED RED
+
BRIGHT
DIM
HIGH
ENERGY
LOW
ENERGY
MAIN SEQUENCE90% of all stars,
including the Sun, fall along a broad strip called
the Main Sequence.
RED RED
+
BRIGHT
DIM
HIGH
ENERGY
LOW
ENERGY
•Main Sequence stars are related in that they have
similar internal structure and function similarly.
RED RED
+
BRIGHT
DIM
HIGH
ENERGY
LOW
ENERGY
Red Giants •Located in the upper right of the HR diagram, Red
Giants are large, cool, and luminous.
•They are about 100 times the size of the sun.
RED RED
BRIGHT
DIM
HIGH
ENERGY
LOW
ENERGY
White Dwarfs Small, dim, hot stars that
are in the lower left of the H-R diagram.
RED RED
+
BRIGHT
DIM
HIGH
ENERGY
LOW
ENERGY