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Old 24-04-2010, 10:20 AM
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trent_julie
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Join Date: Nov 2008
Location: Canberra
Posts: 581
Hey all,

I had a bit of a hunt around after reading Vincent's original question. It took me a little bit of searching to try and find some text from a reputable source to back up my assumptions or disprove them completely.

Of my understanding, I couldn't understand that it would make sense to measure from surface to surface within the solar system given the rotation of the Earth on its axis. I thought that this mattered. This rotation of Earth would effect that value of distance to other objects, at a rate of up to roughly 15deg/h or 6000km/h assisting or retarding from a fixed point on Earth whilst assuming that the object was staying still in its place of orbit.

It seems when giving the distance from the Earth surface to the Moon surface, it is done by calculating the distance to the mathematical centres at a particular point in time then removing the radius of the Earth and Moon.

Consequently, when stating distances from object to object it is convention to state the distances between the objects mathematical centres rather than an observational frame of reference which could only give a distance from surface to surface at an instant in time e.g. bouncing a LASER of the surface of the moon.

Using the mathematical frame of reference rather than the Observational frame of reference negates my Earth's rotation problem. (in which I am yet to find the equation for how it does effect the observer)

In Dot point 52 of the link below Beth Barber of NASA states the convention for stating distances.
http://helios.gsfc.nasa.gov/qa_earth.html

and for further reading,
http://www.davidcolarusso.com/astro/

Thanks for asking that question Vincent, It made me hunt around for answers rather than be spoon fed answers via podcast. This information hunt has helped me come to the conclusion that the reason that when I Image Jupiter, the reason I have blue or red edges, is not because of my poor image processing, and definitely not because of chromatic aberration, but because of Jupiter is red shifting one side and blue shifting the other.......Jokes.

I am sure the forums local astrophysics buffs will be happy to explain in more depth and if I am utterly incorrect please tell me so!

Cheers,

Trent

Last edited by trent_julie; 24-04-2010 at 10:23 AM. Reason: typos
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