Brightness of Mars as observed from earth.

[ybk]

Hi, there's a question that's really annoying me. I hope you guys could help me with it!

 

It is observed that Mars is somewhat brighter when in opposition (ie. sun- earth - mars in that order) that at other times. How can this be explained using

a) The Ptolemaic model and

b) The Copernican model of the solar system.

(Assume that Ptolomy's construction describes the actual motion of the planet)

 

 

Well, for the first part: the rays of the sun shine on mars, whereas if mars was on the other side, u wouldn't be able to see it since the sun would be blocking the way.

 

For part b, mars would be the shortest distance away from the sun in that position; therefore, it'll appear brighter.

 

 

Any help would be great.

 

Also if you can explain that using "retrograde loops" and "epicycle" it'd be even more helpful

 

 

Thanks a lot!!!

[Bubba]

I think that your trying to over complicate the problem.

Mars looks brighter in opposition because it is closer to earth.

 

The brightness of an object is proportional to 1/r^2, where r is the distance to that object. Draw a plot of y= 1/x^2 and look at how there is a steep increase in y for a small decrese in x (at small x values), hence as mars comes a little closer it becomes much brighter.

 

I think "retrograde" and "epicycle" are probably inapropriate terms to be thinking of here.

[swansont]

I think "retrograde" and "epicycle" are probably inapropriate terms to be thinking of here.

 

Why so, given that the mention of the Ptolemaic model?

 

Epicycles were used in the model of a geocentric system with circular orbits, to explain what was observed. Google is your friend here.

[ybk]

Why so' date=' given that the mention of the Ptolemaic model?

 

Epicycles were used in the model of a geocentric system with circular orbits, to explain what was observed. Google is your friend here.[/quote']

 

true true

 

question = answered !

 

w00t!!!

 

But on a 26k connection, it's darn annoying.

[gnpatterson]

As far as the position of the planets might be concerned I had assumed that the Ptolemaic model was accurate in the angular position but failed to give the radial position at all accurately. So would fail to give predict the relative brightness of the planets. I would also assume that the system did not neccessarily recognise the source of the planets light as being reflected from the sun.

 

I know that I was shocked to find out that the system of epicycles that ptolemy used did not correspond to that of our approximate orbit around the sun added to all the planet's approximate orbits. Perhaps this question is to make sure that you are clear on this concept.

[positron]

But what happens in the copernicun model?

is it due to mars blocking out the earth if it is in the other side?

[positron]

sorry, i meant the sun blocking out mars

[W32.Blaster]

Does this have anything to do with the angles or positions in which light is reflected of Mars and towards Earth?