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|Cepheid ||dark matter ||differential rotation
|galaxy ||globular clusters ||Milky Way
|period-luminosity relation ||Population I ||Population II
|rotation curve ||RR Lyrae ||standard candle
- Inverse square law (standard candle): distance to the standard
candle = (calibration distance) × Sqrt[(calibration
brightness)/(apparent brightness)]. Calibration distance is either 10 parsecs
or it is the distance to a similar object at a known distance.
- Orbital speed = Sqrt[(G
× (enclosed mass))/(star's distance from the galactic center)], where the
enclosed mass is the mass of the galaxy inside the star's orbit, and
G is the gravity constant.
- Enclosed mass = (orbital speed)2
× (star's distance from the galactic center) / G, where
G is the gravity constant.
- What is the name for our galaxy and what kind of galaxy is it?
- How big is our galaxy? How many stars are in it and how do we know?
- How are Cepheids and
RR-Lyrae stars considered to be standard candles? How can you find their
- How can you use
the period-luminosity relation to find distances?
- Why do variable stars like Cepheids, RR-Lyrae stars, and Mira variables
vary in brightness?
- Where are we
in the galaxy and how do you know? How can the distribution of globular clusters
tell you about our place in the Galaxy?
- What are the four basic components of our galaxy? Where would old stars
be found? Where would stars with very small amounts of ``metals'' (elements
heavier than helium) be found? Where are new stars being formed? Where would
stars enriched with ``metals'' be found?
- If you could analyze the spectra of 10 stars every second, how many
would it take you to check every star inside the Sun's orbit that is in
our half of the Galaxy? [Hint: used the ``enclosed mass'' graph, divide by
2, and our Sun's distance from the center = 27,000 light years (8,400
- What are the theories for how spiral arms are formed and maintained? What
are the verifiable predictions made by these theories?
- How does the density wave theory explain why stars form in spiral arms?
Also, contrast it with the explanation given by the self-propagating star
- How do astronomers know the dark matter halo (corona) exists if
it does not radiate anything our telescopes can detect?
- Scientists are advocating a focussed search for extra-terrestrial
intelligence that looks at stars
relatively abundant in elements heavier than helium because those are the
elements from which life could possibly form. What part(s) of the Galaxy
would such stars be found and what are the distinguishing orbital
characteristics of such stars?
- If very old stars tend to be metal-poor, how could you explain the presence
of recently-formed stars that are metal poor?
- How do astronomers know that there is a very massive black hole at the center of
- If there were no black hole in the center of the Galaxy, how would the
orbits of the stars near the Sun be affected? (Hint: compare the mass of the
black hole to the total mass inside the Sun's orbit [black hole mass/total
enclosed mass]---would the gravity change significantly?)
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June 10, 2010
Is this page a copy of Strobel's
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