Talk:Standard gravitational parameter

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Thanks for this great info. I'm trying to use it to calculate the orbital distance between two hypothetical stars. But I have become quite lost in the formulas. I am no math wiz - obviously - so that may expain why. I'm having trouble figuring out how to connect the formulas together. As well as determining what values to use for some of the items such as Mass (M). Is it in solar masses? kg? Plus, what is "<<"? It can't mean less-less than <grin>. Sorry about all this -- I guess I'm just one of those lost souls who need an example after the formulas. BY THE WAY: These pages are really great! They helped me develop a table that tells what the Apparent Magnitude of any object is at any given distance! Only took me all night to write it, so my own apparent magnitude was pretty dim! Tesseract 501@aol.com

I am glad you like Wikipedia. "<<" means "much less". M can be taken in kg. Note the difference between m^3 and km^3.--Patrick 12:27, 19 August 2005 (UTC)
Thank you Patrick. "Much less" being a relative term, I suppose. When I only get two slices of pizza instead of four, I consider it <<. I'm still struggling with the Gravitational Constant and the SGParameter. It all started when I just tried to calculate Orbital Periods for hypothetical objects. The various websites seem to give info along the lines of "if planet was .68 AU from the star, its Orbital Period would be 228 days. If it was 0.01 AU, its Orbital Period would be 18 days. Etc." So, I tried to plug in value into the T = 2\pi\sqrt{a^3/\mu} formula for determining orbital period (small body around central body) -- and the bit-more involved formula for two bodies orbiting each other. It's straightforward enough to get the Semi-Major Axis values and the masses. But, the plugging the Gravitation Constant into the equation is where I'm a bit stuck. I'm not sure how to incorporate the kg-1, m3 and s-2 aspects.
I wish the page had at least one example using hypothetical objects (one for the small-body equation, and one for the two-body equation).
Thanks again -- I've seen your work on other pages. It is really great stuff. Inspiring.
Tesseract501@aol.com (August 27, 2005)
Thanks. The "kg-1, m3 and s-2" mean that distances should be in meters, not AU, and times in seconds, not days. Anyway, you may not need G, you need the sum of the two μ-values; for those you can e.g. multiply the number of solar masses by the μ-value for the Sun.--Patrick 00:13, 28 August 2005 (UTC)

[edit] Unit Conversion

This might go better in the units of measure area, but since there were already people talking about it in this area, I'll stay here for the moment. :)

Patrick, could you give an example of converting, for example, km3/s-2 to m3/s2? I understand how to convert km3 to m3 (multiply the value by 1000, since there are 1000 meters in a kilometer), but I don't understand what unit of time s-2 is referring to, or how to convert between different exponentations of the same time unit, which is what it sounds like it's asking me to do. --Kintar 15:04 CST, 06 October, 2005

1 km3s-2 = 1 km3/s2 = 1,000,000,000 m3/s2.--Patrick 22:17, 6 October 2005 (UTC)
I'm not really sure how km3 is the same thing as m3. I understand that GM is m3s-2, but wouldn't that only make the equation kms-2? So is the equation on the front page correct?--oscabat 18:13 CST, 06 January 2005.
Perhaps you're misunderstanding the difference between km and m^3. 1 km = 1000m . 1 km^3 = 1 km*km*km = (1000m)*(1000m)*(1000m) = 1'000'000'000 m^3 = 1*10^9 m^3. The units on the front page are correct. I would prefer that the units of GM be changed to m^3/s^2. SI units all the way. DavidMcKenzie 20:45, 1 August 2007 (UTC)

[edit] Moon GM parameter

I thought that the Moon should have a listing in that table, especially if Ceres has! referenced from here: [1]