# Need astronomy help quick



## rdf8585 (Nov 19, 2004)

Choose Best answer, multiple choice

10. Recently astronomers have observed stars and other objects that orbit the center of the Milky Way Galaxy farther out than our Sun, but move around faster than we do. How do astronomers think such an observation can be explained?

(For 4 points.)
- all these faster-moving objects must be escaping from the gravity of the Milky Way and will soon be lost to our galaxy
- each of the faster-moving objects must be the result of a supernova explosion, giving them extra speed
- it is the Sun that is moving too slowly because of a collision billions of years ago
- there must be a great deal of dark matter outside the orbit of the Sun whose gravitational pull explains the faster motions we see out there
- there is currently no explanation for this phenomenon

11. How do astronomers measure the mass that the galaxy contains inside the orbit of the Sun?

(For 4 points.)
- they measure the distance to the center of the galaxy and the period of the Sun's orbit and then use Kepler's 3rd law
- they count the number of stars one by one and multiply by the average mass of the star
- they add up all the observations at 21-cm wavelengths, because the mass of hydrogen gas is far greater than the mass in all the stars
- they measure the masses of many other spiral galaxies nearby and then take an average
- there is not way to get the mass of something as big as our galaxy

12. Which of the following statements about dark matter in the galaxy is false?

(For 4 points.)
- most of it cannot at present be observed with our telescope, we only know of its existence from the gravity it exerts
- while the dark matter cannot be observed with our present day instruments, we still have a pretty good idea what it consists of
- our measurements suggest that there may be as much as ten times more dark matter in the Galaxy than the matter we have been able to observe
- dark matter appears to be distributed in a giant corona around the galaxy
- we can pretty much rule out the idea that the dark matter is made mainly of vast clouds or regions of hydrogen gas 


13. Which of the following is evidence that the formation process of our galaxy may have included collisions with smaller neighbor galaxies?


(For 4 points.)
- the presence of millions of new stars, recently formed from clouds of gas and dust
- the existence of supernova remnants in the galaxy's disk
- the observation that objects outside the orbit of the Sun are moving around the galaxy faster than we expected
- the observation that globular clusters are arranged in a spherical 'halo' around the galaxy
- the observation of long moving streams of stars that continue to orbit through our galaxy's halo


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## ColdFury (Nov 6, 2003)

The answers to the last two are the last answer, and the first answer respectively. The other questions are much too vague and ill-posed.


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## michaelg (Jan 29, 2005)

11 I think:

they measure the distance to the center of the galaxy and the period of the Sun's orbit and then use Kepler's 3rd law

although somebody else who's actually taken astronomy might want to verify.


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## michaelg (Jan 29, 2005)

And for 10 I would say:

- there must be a great deal of dark matter outside the orbit of the Sun whose gravitational pull explains the faster motions we see out there 

referring to the dark matter warping the galaxy.


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## ColdFury (Nov 6, 2003)

Actually I think the "We don't know" answer for that one is the best, but the question is stated oddly.


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## matt404 (Feb 8, 2006)

The answer to number 12 I would say is "while the dark matter cannot be observed with our present day instruments, we still have a pretty good idea what it consists of." That's the only false statement there. There are a lot of theories as to what dark matter might be, but at this point we really don't know for sure. The last answer there is a true statement. If dark matter were large clouds of hydrogen gas, it would be visible by either blocking light emitted behind it (like dark nebulas do) or by emitting it's own light (like an emmision nebula).


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