Iskender Piyale-Sheard AST201 MIDTERM 2 Study Notes
Hydrostatic Balance Thermal pressure from heat generation pushes outward. Gravity
1. Two protons fuse and make a deuterium nucleus (1 proton and 1 neutron). This
2. The deuterium neucleusand a proton fuse to make a nucleus of helium-3 (2 protons,
1 neutron). This step also occurs twice.
3. Two helium-3 nuclei fuse to form helium-4 (2 protons, 2 neutrons) releasing 2 excess
protons in the process.
4. Overall, 4 protons fuse, and the product is a helium 4 nucleus, gamma rays,
neutrinos, and positrons.
Neutrinos barely interact with other matter. They can only interact via gravity and the
strong nuclear force. They are not subject to the forces of electromagnetism.
Hydrogen atons can only fuse in the suns core. It is not hot enough anywhere else.
Equilibrium in Sun:
1. Drop in pressure
2. Leads to a large decrease in fusion
3. This lowers the core pressure.
4. The core contracts due to gravity and heats up
5. The fusion is restored to normal rate.
Luminosity is the intrinsic brightness of an object.
Stars are blackbodies: Their colours are determined by their temperatures.
Every star emits light of all wavelengths. Their colours are determined by the colour of light
they emit most of.
www.notesolution.com www.notesolution.com th
The Inverse Square Law of Light:
Apparent brightness is related to the luminosity such
Brightness = luminosity
4(distance to star)
Each star has absorption lines that make up a stellar spectrum. These absorption
lines correspond to the chemical elements in the stars atmosphere.
Absorption lines indicate a stars composition
Strength of specific absorption lines indicates temperature.
The strengths of the lines depend on the temperature of the star.
You can determine a stars temperature more precisely this way, than just
looking at its colour.
Spectral Class - OBAFGKM - Oh, Be A Fine Girl Kiss Me
1. Weak in cool stars because the temperature is too low to excite it.
2. Strong in warm stars because they can excite it.
3. Weak in hot stars because the hydrogen becomes ionized.
To measure the mass of stars we rely on binary stars.
Most stars are in binaries.
1. Spectroscopic binary:
You can detect a binary star system by analyzing the doppler shift of a star. We can
www.notesolution.com see the doppler shift of a star in a binary system. Redshift, blueshift depending on
whether it is approaching us or moving away.
2. Eclipsing Binary:
If one star passes in front of another, the apparent brightness decreases.
1- Light from both.
2- Light from larger one is a bit eclipsed by smaller one.
3- Light from both
4- Light from smaller one is completely eclipsed by larger one.
HertzsprungRussell (HR) diagram
Main sequence stars