                 
|
Spectral Type
[Key Words]
[Star Colors and
Spectral Class] [Red-shift,
Blue-shift]
[The Raisin Cake
Model]
Star
Colors and Spectral Class
 When pure white
light is split up by a prism, it shows all the colors of the
rainbow. This is known as the light
spectrum. Because of what stars burn, they do not give off
pure white light. Because of this, some colors are missing from
the light spectrum. Certain types of stars have certain types of
these "fingerprints," known as spectra.
This fingerprint is what determines where the star's spectral
class is. There are a total of seven main spectral classes.
Over 99% of stars can be put into one of seven different spectral
classes. Spectral appearance mainly depends on the temperature of
the star's atmosphere. Stars are labeled in the following order
(from hottest to coolest) "O, B, A, F, G, K, M." A good
way to remember is "O, Be A Fine Girl/Guy Kiss Me."
There are also other categories, such as R, N, and S. These types
of stars have a strange abundance of heavy-metals. There are Q
type stars for novae, W for Wolf-Rayet stars, and T for T Tauri
Stars, among others.
A star's spectral class is further refined by how
hot the star is. There are 10 categories for this (0-9). For
example a very hot star would be O0 (O zero). Luminosity
classes are also involved in classification. Luminosity
classes include supergiants, bright giants, giants,
sub-giants, dwarfs
(stars on the main sequence), and white
dwarfs. Each luminosity class is designated on the following
manner:
supergiants--------Ia, Iab, Ib
bright giants-------II
giants-------------III
sub-giants---------IV
dwarfs------------V
white dwarfs-----VI
A complete spectral designation uses all of the
above elements. A good example of using the complete spectral
classification system is our sun, which is a G2V (read
G-two-five.)
Red-shift,
Blue-shift
As an object moves away or comes closer, their
spectrum is altered. Imagine being at a race track and having a
car go past you. As the car comes closer, the sound waves are
compressed in front of the car, and so the pitch is higher. As
the moves farther away, the sound waves are stretched, and so the
pitch is lower. This same concept applies for light as well. The
farther you move into the longer wavelength part of the spectrum,
the more red it looks. This is called a red-shift.
The farther you go into the smaller wavelength part of the
spectrum, the more blue it looks. This is called a blue-shift.
Therefore, if an object is moving away from you, then the
wavelength will be spread out more, and it will appear more red.
Here is a normal light wave
Here we will represent it in green (it is the
middle color on the spectrum)
As the wave gets stretched out, it changes to red
As the wave gets compressed, it changes to blue
The
Raisin Cake Model
Edwin Hubble noticed that the farther an object is away from
earth, the faster it is moving away. This can be explained with
the raisin cake model. Picture a raisin cake before it's been
baked. As the baking process begins, the bread begins to rise and
all the raisins spread out. Closer raisins spread out less than
farther raisins because there is less dough between them. This
same concept applies with the universe. Picture the raisins being
galaxies.Everything is spreading out, and the farther away the
object is, the faster it is moving away. This creates different
intensities of red-shifts. The red-shift can now be used to find
out how far away distant objects are.
Previous Topic: Special
Stars Next Topic:
Constellations
[Key Words]
[Star Colors and
Spectral Class] [Red-shift,
Blue-shift]
[The Raisin Cake
Model]
|
