13 Dec 2007

Astronomy 103 Review Lecture

Final Exam:

10:05 A.M. TUE. DEC 18

Chamberlin 2301

13 Dec 2007

Reminders• Pick up all homework and discussion handouts that

you haven’t gotten back from me!• If any HW wasn’t returned, YOU are responsible for

making sure grade was recorded! • TA Review Session (all Q&A)

– 6pm-8pm Friday December 14th– Chamberlin 2241

• New stuff: Units 54, 55, 57-68,70-72, 74-84. Old material: Units 1-30, 49-52.

• Katie is GONE and may not have email access after the 15th.

13 Dec 2007

Helpful items on my website:

• Equation Sheets from Exam 1 & 2

• Practice Questions from Exam 1

• Exam 2 Review Lecture

• Homework Solutions

• (NEW!) Review questions for new material

• (NEW!) This review lecture

13 Dec 2007

Topics to Review - Part 1• The basics: metric system, unit conversion, scientific

notation, size scales• Earth, Moon, Sun, Solar System, Milky Way overview • Special Units: Parsec, AU, light year, etc• Celestial Sphere• Causes of: Days, seasons, phases of moon,

precession, eclipses, retrograde and prograde motion of planets – Why do days get shorter in winter, why is it colder, etc?

• Solar v. Sidereal day

13 Dec 2007

Topics to Review - Part 1• How did we first determine the shape and size of the

earth? The moon? The sun? Who made those discoveries?

• Geocentric v. Heliocentric models of the solar system- how did we decide?

• Angular diameter - what is it, how is it related to an objects real size (linear diameter) and its distance from us?

• How were distances to other planets measured (and who measured them)?

• What did Brahe, Kepler, Galileo, Newton contribute to astronomy?

• Tides - cause, timing of high and low tide

13 Dec 2007

Topics to Review - Part 1• IMPORTANT TO UNDERSTAND BASIC PHYSICS

– Kepler’s Laws – Newton’s Laws (inertia, F=ma, equal and opposite reactions)– Gravity, Newton’s Universal Law of Gravitation– Surface Gravity– Circular motion and orbits– Centripetal Force– How to get masses from orbital speeds– Escape Velocity– Conservation of energy, kinetic energy, potential energy– Conservation of angular momentum

• Check out your equation sheet from Exam 1!

13 Dec 2007

Angular Size

13 Dec 2007

I drop a 10kg mass and a 5kg mass from 4 feet off of ground.When to they hit?

a. same timeb. 10 kg mass hits firstb. 5 kg mass hits first

WHY? Hint: What is difference between mass and weight? Does acceleration due to gravity depend on mass?

13 Dec 2007

€

Vcirc =GM

d

2

3

YR

AUBA P

aMM =+

How do you calculate the mass of a star if you can measure the orbital velocity of a planet orbiting around it?

13 Dec 2007

What happens if the string breaks? (INERTIA!)

13 Dec 2007

Calculating Escape Velocity

• From Newton’s laws of motion and gravity, we can calculate the velocity necessary for an object to have in order to escape from a planet, called the escape velocity

€

Vesc =2GM

R

13 Dec 2007

Topics to Review - Part 2• Nature of Light• Blackbodies• Kirchoff’s Laws• Doppler Shift• Telescopes• Parallax• Sun

– Parts of the sun– Hydrostatic equilibrium (“sun’s thermostat”)– Sun’s source of energy (fusion)

http://www.astro.wisc.edu/~devine/exam2review.ppt

13 Dec 2007

Topics to Review - Part 3• Luminosity of stars-- Stefan Boltzman’s Law• HR Diagrams, Stellar evolution • End stages of stars -- white dwarfs, neutron stars,

black holes• Active Galactic Nuclei• Galaxy types, and how galaxies form• Interstellar medium• Standard candles and distances• Cosmology

– Big bang, expansion, Hubble Law– Structure of universe, CMB, how did matter form?– Fate of universe

• Other life in the universe?

13 Dec 2007

Star Formation

13 Dec 2007

Tracking changes with the HR Diagram

• As a star evolves, its temperature and luminosity change.

• We can follow a stars evolution on the HR diagram.

• Lower mass stars move on to the main sequence, stay for a while, and eventually move through giant stages before becoming white dwarfs

• Higher mass stars move rapidly off the main sequence and into the giant stages, eventually exploding in a supernova

13 Dec 2007

Tracking changes with the HR Diagram

• 0.5-8 solar masses: WD

• 8-25 solar masses: Neutron star

• > 25 solar masses: black hole

• >50 solar masses - what do you think?

• What about “quark stars”?

13 Dec 2007

The Hourglass Nebula

13 Dec 2007

Neutron Stars (Pulsars)

• A neutron star spins very rapidly about its axis, thanks to the conservation of angular momentum

• If the neutron star has a magnetic field, this field can form jets of electromagnetic radiation escaping from the star

• As the neutron star spins, the jets can sweep past earth, creating a signal that looks like a pulse.

• Neutron stars can spin very rapidly, so these pulses can be quite close together in time!

13 Dec 2007

Black Holes• If a stellar core is

massive enough, it will not stop collapsing when it becomes a neutron star.

• Once something, including a photon, crosses the Schwarzschild radius (or event horizon), escape is impossible.

• Can Hawking Radiation Escape?

13 Dec 2007

Milky Way

13 Dec 2007

Spiral Galaxies

13 Dec 2007

Elliptical Galaxies

13 Dec 2007

Irregular Galaxies

13 Dec 2007

Active Galactic Nuclei & Quasars

• Quasars are small, extremely luminous, extremely distant galactic nuclei

• Luminosity and jets likely come from matter falling into big black hole (millions of solar masses) at the galaxies centers

• Was our galaxy an AGN once?

13 Dec 2007

Mass Transfer and Novae

13 Dec 2007

The Chandrasekhar Limit and Supernovae

13 Dec 2007

Type 1a Supernova – Another standard candle!

• Variable stars are also standard candles-- how, why?

• Um, what’s a standard candle? Why do they matter?

13 Dec 2007

Large Scale Structure in the Universe

• Galaxies tend to form long chains or shells in space, surrounded by voids containing small or dim galaxies

• This is as far as we can see!

13 Dec 2007

The Hubble Law

• In 1920, Edwin Hubble developed a simple expression relating the distance of a galaxy to its recessional speed.

• V = H d– V is the recessional

velocity– D is the distance to the

galaxy– H is the Hubble Constant

(70 km/sec per Mpc)

• This was our first clue that the universe is expanding!

13 Dec 2007

A Timeline of the Universe

13 Dec 2007

Clumpiness in the CMB

13 Dec 2007

The Origin of Helium

• Immediately after the Big Bang, only protons and electrons existed

• Shortly after the BB, temperature and density was high enough for deuterium to form by fusion

• After 100 seconds or so, temperature cooled enough so that deuterium could fuse into helium nuclei

• The temperature continued to cool, and fusion stopped after a few minutes.

• Big Bang theory predicts that around 24% of the matter in the early universe was helium, which matches what we see.

13 Dec 2007

Density of the Universe• Like throwing a ball in the air-- if

you throw it with enough energy to get past the density of earth (so it goes faster than escape velocity), the ball will go on traveling into space forever

• Similarly, the density of the universe and the energy provided by big bang determine its ultimate fate

• This confusing graph shows the possible options-- expand forever, become stable and stop expanding, or start collapsing… OR….

13 Dec 2007

The Universe is ACCELERATING Apart?!?

• In our ball example, this would be like throwing a ball in the air, and watching it get FASTER as it got further away from you. Where is that extra energy coming from?

• DARK ENERGY– Not yet well understood

or explained. Stay tuned…

13 Dec 2007

Other Possible Curvatures of Space

• In addition to a closed, or positive curvature of space, there are two other options– Space could be flat, or have zero curvature– Space could be curved away from itself, or have

negative curvature– Geometry behaves differently with each curvature!

13 Dec 2007

21 cm Radiation

• Most interstellar gas is very cold, so it emits very few photons.

• The electron in a hydrogen atom has two energy states– Spin up and spin down– Spin up has slightly more energy

than spin down

• If the electron’s spin flips from up to down, it must emit a photon of the same energy as the energy difference between states

• This 21 cm radiation (HI emission) is detected by radio telescopes, allowing the study of these cold clouds

13 Dec 2007

Gravitational Lenses

• Dark matter warps space just like ordinary matter does

• The path of light rays bends in the presence of mass

• A galaxy or other massive object can bend and distort the light from objects located behind it, producing multiple images

• This is called gravitational lensing

13 Dec 2007

Life Elsewhere? Drake Equation

Probability of life on other planets=?