Course Announcements Smartworks Chapter 13: Friday-ish No Class Friday (Good Friday) Smartworks Chapter 14: Next Week Apr. 2 – Last day to drop a class. 2 Dark night observing sessions left: Mon. Apr. 13 & Thurs. Apr. 16 Reports are due Wed. Apr. 22 Solar Rotation Project due Mon. Apr. 27 Exam-3: Fri. 4/10
Astronomy in the Fall, 2015 ASTR-1010/ Planetary Astronomy + Lab (H,R) ASTR-1020/ Stellar Astronomy + Lab (R) ASTR Problems in Planet Astronomy ASTR Intro. to Observational Astronomy ASTR-4000/4001 – Astrophotography & Lab ASTR-3030/3031 – Methods & Techniques in Astronomy(*) ASTR-4170 – Special Topics in Astronomy (?) Photometry and Filter Systems
Star Clusters We’ll come to these, but star clusters are the key to understanding stellar populations. Same age. Same chemical composition. Same distance.
Concept Quiz—The Main Sequence Which of the following statements about the main sequence is not true? A.Hotter stars are more massive. B.More massive stars are more luminous. C.Hotter stars are more luminous. D.Most main sequence stars are more luminous than the Sun.
Not all stars are on the main sequence. Remember Stefan- Boltzmann. Some stars are cool but very luminous: giants or supergiants. Some have low luminosity but are very hot: white dwarfs. Different luminosity classes.
The H-R Diagram
Different temperature stars have different habitable zones: regions where life as we know it could be supported. Water must be able to exist as liquid. So far, only a few planets have been found in the habitable zones of their stars.
The Sun is the Largest Object in the Solar System The Sun contains more than 99.85% of the total mass of the solar system If you put all the planets in the solar system, they would not fill up the volume of the Sun 110 Earths or 10 Jupiters fit across the diameter of the Sun How big is the Sun?
How Do You Describe a Stable, Main Sequence Star? 4 Structure Equations: d M /dr = 4 r 2 dP/dr = G M /r 2 dT/dr = -3 L / r 2 T 3 (rad) dT/dr = 0.4(T/P)dP/dr (conv) d L /dr = 4 r 2 4 Auxiliary Equations: P = kT/ m H (IGL) P = k (AGL) = 0 Z(1 + X) T -3.5 (opacity) = 0 X 1 X 2 T (Energy gen.) = ~4 (pp); ~20 (CNO)
How Do You Describe a Stable, Main Sequence Star? Loosely: A self-gravitating sphere of mostly Hydrogen (74%) and Helium (24%) in hydrostatic equilibrium with the inward gravitational force balanced by an outward radiation pressure, powered by Hydrogen fusion in the core.
Structure of the Sun We only see the outer layers of the Sun. Physics tells us about the interior. Key idea: hydrostatic equilibrium. At each point there’s a balance: Outward pressure = inward force of gravity. Rate of energy emitted = rate produced in the core. Density, temperature, pressure increase towards the center.
Interior of the Sun
We only see the outer layers of the Sun. Physics tells us about the interior. The Sun must be in balance to have existed in a constant state for billions of years.
At each point in the Sun there is balance: Hydrostatic equilibrium: outward pressure = inward force of gravity. Solar energy production must equal what is radiated away.
Density, temperature, and pressure increase toward the center creating the necessary conditions for nuclear fusion.