Help with astronomy homework please.?

[MEEEEEEEEE]

Suppose we lived on Pluto and not Earth. Pluto orbits the Sun at an average distance of roughly 39.5 AU, and (you could calculate this from Kepler’s 3rd Law) it takes more than 248 years to complete an orbit. (All of this information is relevant.) If we lived on Pluto, astronomers would be able to measure the distances to stars in our Milky Way galaxy much better than they can from Earth.
a) Explain why and how astronomers could determine accurate distances to many, many more stars if we lived on Pluto.
b) In what way is measuring the distances to stars still easier to do from Earth than it would be from Pluto (even if we could establish an observatory on Pluto easily)?

I don't understand how to do this one. Will someone either give me the answer or a clue or something?

 

[Kyle M]

A) many distances are measured using parallax. This is looking for small changes in position and angle of stars in the sky over a half year period. This can determine distance using trigonometry. Pluto would be more accurate and more stars would be able to be measured because Pluto has a larger radius in its orbit. If the base is larger then distances can be drawn farther before angles become insignificant.

B) It would not be practical to use Pluto's parallax to measure distances because Pluto takes over a hundred years to go from one side of its orbit to the other, while Earth only takes 6 months.

 

[Vincent G]

Stars that are not too distant (say, less than a couple hundred light years -- reaching further requires orbital instrumentation, but that is a secondary point) may have their distance evaluated by the apparent motion they have against a more distant stellar background simply from the fact the Earth is one side of the sun at one point and at the other side 6 months later. Basically, the Earths' orbit is the base of a narrow triangle, and the angle allows determination of the distance to the star. Now, move to Pluto and the base of the triangle is much bigger, allowing the accuracy of the angle measurement to be better, or the range of the stars that could be measured to be longer.

For the second question, the answer is quite simple: you'd have to wait 124 years to get a measurement at maximum accuracy on Pluto, as opposed to 6 months on Earth... And since Pluto moves so slow on its orbit, observations 6 months away on Pluto would be far less accurate than those made on Earth, so you'd have to wait decades on Pluto to get any kind of better measurement than on Earth.
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