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12 Cards in this Set

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Know how Hubble was able to prove tha Andromeda was a seperate galaxy not part of the milky way.
He used Cephiad variables (which he found by noting the variation in their luminocities) as standard candles for finding the distance to the andromeda galaxy. The distance was too great to be part of our own galaxy.
What is a spiral galaxy?
The milky way is a typical spiral galaxy. It has a disk with spiral arms, a nuclear bulge and a halo. These have very little gas and dust. The nuclear bulge is reddish because it contains old stars, but the spiral arms are bluish because they have new star formation going on in them.
What is an elliptical galaxy?
This looks like a spiral galaxy without the disk. (So a nuclear bulge and a halo.) They hardly have any inner stellar gas and dust at all. These only really contain old stars so they have a reddish hue.
What is an irregular galaxy?
These are everything else. Sometimes they look irregular because of recent bursts of star formation in them. These have a lot of gas and dust.
What is a standard candle?
An object for which we know the luminocity. This lets us derive the distance to it.
What is stellar paralax?
The distance between where an object appears from earth as earth moves. Lets us figure out distance but only in close objects (within 300 LY).
What is fitting the main sequence of a star cluster used for?
You have an H-R diagram with the distances of stars you know by parallax. Have absolute magnitude on one axis and color index on the other. Compare that to the observed apparent magnitude of the cluster and you can ascertain the distance between them (exactly like m-M=5logd-5)
What are Cephiad variables used for?
Standard candles whose luminocity we know. Thus we can derive their distance.
What are white dwarf supernova used for?
These are the best standard candles because they are always stars of the same mass so their absolute magnitudes are always right on.
What is Hubble's Law used for?
Galaxies farther away from us are moving farther away from us faster in a direct proportion. If you observe the redshift of an object and it's huge, it's likely because of the expansion of the universe. It relates redshift and velocity. It gives evidence for an expanding universe. We can use this to estimate the age of the universe since we have the distance and Hubble's constant we can get the velocity and therefore the age.
What is our local group?
Us, the andromeda galaxy, one other spiral galaxy, a few dozen other smaller galaxies, and our little bitty local cluster of galaxies.
What is the Virgo cluster?
The next reasonably large cluster out from us. The overall distribution of galaxies is like in that video we watched, where they are like soap bubbles (e.g. voids but matter around the voids where the galaxies are).