Astronomy 1 – Fall 2014
Lecture 17; December 11, 2014
What will you remember about
this class in 10 years?
(iclicker Question)
A.
B.
C.
D.
E.
The lunar eclipse?
The partial solar eclipse?
Seeing Mars, M31, and Algol in the telescopes?
The demos (spectral lines, telescope optics, sunset, etc.)
Other stuff
Review: The Celestial Sphere
• Why does the night sky change?
1.
2.
3.
4.
5.
Earth’s rotation
Earth’s orbital motion about the Sun
The moon’s orbit around the Earth
The orbits of the outer planets about the Sun
The precession of the Earth’s spin axis
Earth’s Rotation
Precession of Earth’s Rotation Axis
Earth’s Orbit
East
West
North
South
Celestial Equator
Let’s Check
(iclicker Question)
Retrograde Motion of Planets
“Wandering” of Uranus in 2014
Final Exam (Tuesday Dec. 16 4-6 pm)
• Bring a large, red scantron, calculator, and #2 pencil.
– NOTE: COMPLETELY FILL IN THE BUBBLES!
• An opportunity to demonstrate that you’ve learned
material you missed on the midterms.
• Also covers chapters 21, 22, and 23.
• 85 multiple-choice questions
– 31 questions on new material from ch. 21-23
– 54 questions evenly divided between concepts
emphasized on midterms 1 and 2.
• Cumulative & focused on concepts.
Since Midterm 2
Key Topics from ch. 21
• Special Theory of Relativity
The laws of physics are the same
in any (intertial) reference frame
– The speed of light is the same
to all observers
– An observer will note a
slowing of clocks and a
shortening of rulers that are
moving with respect to them.
– The above is all selfconsistent as we showed in
the discussion of muon decay
in Earth’s atmosphere.
• General Relativity Gravity
cannot be distinguished from any
other acceleration
– Mass-energy distorts space-time,
and the resulting curvature of
space-time accelerates particles
– Predictions for bending of light,
gravitational redshift, and
gravitational waves all verified
by experiment
• Black HolesStellar corpse larger
than ~3 M0
– Found at center of Milky Way
– Schwarzschild radius
Since Midterm 2
Key Topics from ch. 22
• Milky Way Galaxy Contains
~2x1011 stars
– Sun is in a nearly circular
orbit 8 kpc from the center
– Stars (Pop I) in disk are young
and metal rich
– Stars in halo (Pop II) are older
and metal poor
– The central bulge has a radius
of 1 kpc and a mass about
1000 times larger than the
supermassive BH.
– Is still growing today via
mergers with other galaxies
• Rotation curves indicate nonluminous matter
• Spiral arms are
– Density waves
– Locations where gas clouds
pile up and trigger star
formation
– Traced by dust lanes and
HII regions
Since Midterm 2
Key Topics from ch. 23
• The Universe contains
billions of galaxies
– Why wasn’t this clear to
Einstein as late as 1920?
– The importance of Hubble’s
discovery of Cepheids in
Andromeda.
– The cosmic distance ladder
• Discovery of the expansion
of the Universe
– Hubble’s Law
– Cosmological redshift
– Redshift as a distance
measurement
• Large-scale structure of the
galaxy population
– Groups, clusters, and voids
– Cosmological principle
• Formation of galaxies
– Small galaxies merged into larger
galaxies
– We can see galaxies at a time when
the Universe was less than onetenth its current age (13.8 billion
years)
• Evolution of galaxies
– Galactic winds
– Mergers (of galaxies and clusters)
Planets, Stars, Galaxies, and the
Universe are governed by the same
laws of physics as laboratory
experiments.
Can you draw some analogies?
The Study of Planets, Stars,
Galaxies, and the Universe is
intimately connected to atoms
Can you give some examples?
Light
• How long does it take sunlight to reach Earth?
Travel to the center of the Galaxy? How can
astronomers take pictures of infant galaxies
less than a billion years old?
• What is light? How do we know?
• How do atoms emit and absorb light?
• What are the properties of the light emitted by
opaque sources such as stars, dust grains,
planets, gas in galaxy clusters, etc?
– Can you give an example of a light source that is
not a blackbody?
The Cosmological Principle states
that the Universe is homogeneous
and isotropic on large scales.
• Is this supported by observations? How?
• Is the Universe the same at all times?
The Universe is a Dynamic Place
• Can you give some examples of objects that
move (and why they move)?
– What is surprising about the motions of stars
within galaxies?
– What is surprising about the motion of galaxies
with respect to one another?
– How much of the moon’s surface can we see?
And why?
Why Astronomy?
• Where did the atoms in your body come from?
• How/When did the Earth and Sun form?
– What will happen to them in another 7 billion years?
• What is the origin of the Moon?
• How many stars are in the Milky Way galaxy?
– How many of them are similar to the Sun?
– Are habitable planets common? How do you know?
• Are there other galaxies like the Milky Way?
– How/when did they form?
– What is their fate?
Astro 1
The End?
My hope is that it’s actually a
beginning that cultivates your
notions about the universe and
your place within it!
• Do you know what were you looking at now?
– Where does moonlight come from?
– Why don’t solar eclipses happen at every new moon?
– What aspect of the formation of the solar system explains
the small size of Mars?
– What is the bulge of M31 (Andromeda Galaxy) made of?
– The color of a star reflects what property of a star?