Kepler's Third Law and a comet

[Gold3nlily]

Homework Statement

Suppose that a comet that was seen in 545 A.D. by Chinese astronomers was spotted again in year 1937. Assume the time between observations is the period of the comet and take its eccentricity as 0.11. What are (a) the semimajor axis of the comet's orbit and (b) its greatest distance from the Sun?

Homework Equations

Kepler's Third Law
T²= [(4pi²)/(GM)]* a³
G = 6.67e^-11
M_e = 5.98e²⁴

The Attempt at a Solution

part a:
T = 1937-545 = 1392 (365d*24h*3600s) = 4.38e¹⁰ sec
e = 0.11

T²= [(4pi²)/(GM)]* a³
solve for a
a = [T²*[(GM)/(4pi²)]]^(1/3)
a = [(4.38e¹⁰)²*[(6.67e^-11*5.98e²⁴)/(4pi²)]]^(1/3)
a= 2.69e¹¹ m

Part b:
Ra = a + ea
solve for Ra with e and a... but I can't find the correct a in first part of question

Whats going on, where did I go wrong?

 

[phyzguy]

You used the Earth's mass - you should be using the sun's mass.

 

[Gold3nlily]

You used the Earth's mass - you should be using the sun's mass.

:face palm:

Thanks so much.

 

[chubbynaveen]

In what way kepler's law affects the motion of the Earth when it goes round the sun.
wil kepler's law apply to man-made satellites also. If so why?

 

[Mike Pemulis]

In what way kepler's law affects the motion of the Earth when it goes round the sun.
wil kepler's law apply to man-made satellites also. If so why?

Well, Kepler's Laws describe any light particle orbiting a very heavy body. So Earth's orbit about the sun follows Kepler's Laws, as do the orbits of satellites about Earth. Does that answer your question?

 

[chubbynaveen]

well ... thanks for your answer about the relation between kepler's law and satellites but could you be more specific, coz its a 30marks question and i need a kind of detailed explanation...

 

[Mike Pemulis]

I won't write your essay for you. For general information on Kepler's Laws, see Wikipedia or your textbook. If you have any specific questions after doing some research, I'm all ears.

 

[chubbynaveen]

How would you obtain the index error of the sextant of the sun "by using its diameter on the arc and off the arc".
kindly give ans. appropriately, coz i know how to just obtain the index error of the sun by using a sextant.