1. The Temperature of a Star
And its Composition

2. The Energy of an Photon
A photon carries energy in inverse relation to its wavelength.
Thus
Short wavelength photons carry more energy
This is why short wavelength/high frequency light carries more energy

3. The hotter something is the more energy it gives off
Thus the hottest stars glow brightest in the shortest wavelengths…
Their“white light” is tinted blue
Cooler stars have a yellow tint to their “white light”
And the coolest have a red tint

4. (See Formula on the Board)
Wien’s law
According to Wien’s Law…
The temperature of the surface of a Star can be found using the brightest wavelength of light (color) that it gives off.
The Formula for this is:
(See Formula on the Board)

5. (Indicating significant trace elements)
Composition of Stars
By studying the absorption/emission spectrum of stars we can find the composition of the star.
All stars are mostly hydrogen and helium but they also have important trace elements
Stars are divided into Spectral Classes
based on their brightest spectral lines
(Indicating significant trace elements)
, and their temperature.

6. Spectral Classes O 28,000 K - 50,000 K. Blue-white Ionized Helium
Class Temperature Color Strong Lines
O 28,000 K - 50,000 K. Blue-white Ionized Helium
B 10,000 K - 28,000 K. Blue-white Helium
A 7,500 K - 10,000 K. White Hydrogen
F 6,000 K - 7,500 K. Creamy Ionized Calcium
G 5,000 K - 6,000 K. Yellow Calcium
K 3,500 K - 5,000 K. Orange Titanium Oxide
M 2,500 K - 3,500 K. Red Titanium Oxide