View Full Version : Earth from Geosynchronous Orbit

Ryback

2004-Mar-25, 01:24 AM

I was thinking, how big would the earth be if observed from a geosynchronous orbit? After some quick calculations, I get a size of 17 degrees field of view. So if an outstretched fist is 10 degrees, it would be almost two fists in diameter.

Can anyone confirm or despute this result?

ToSeek

2004-Mar-25, 01:39 AM

This site (http://www.eumetsat.de/en/index.html?area=left6.html&body=/en/mtp/space/geostationary.html&a=620&b=1&c=600&d=600&e=0) (if you scroll down far enough) says 18 degrees, which sounds like confirmation of your estimate to me.

tlbs101

2004-Mar-25, 06:11 PM

Radius of earth: 6378 km

Kepler's 3rd law:

mu is the gravitational constant -- 398601 km^3 / sec^2 for Earth

P is the period -- 24 hours (86400 sec)

a is the distance of the orbit

http://liftoff.msfc.nasa.gov/academy/rocket_sci/orbmech/kepler1.gif

yields distance of GEO from center of earth 'a': 42164 km

inverse_tangent(6378/42164) = 8.60172 degrees

multiply that by 2 and you get: 17.20 degrees

milli360

2004-Mar-25, 06:45 PM

P is the period -- 24 hours (86400 sec)

That should be 86164 seconds (http://www.badastronomy.com/phpBB/viewtopic.php?p=56095#56095).

yields distance of GEO from center of earth 'a': 42164 km

That the answer you get with 86164 s. With 86400 s, the formula gives you 42241 km.

tlbs101

2004-Mar-25, 08:43 PM

That's why you are the Bad Grad and I am just the very Bad Newbie.

#-o

I got the resultant GEO distance from the same NASA web site that produced the GIF of the formula. You are correct; when I did the math, the numbers came out different, because I didn't take the EXACT rotational time of the Earth into consideration.

Wiley

2004-Mar-26, 01:20 AM

That's why you are the Bad Grad and I am just the very Bad Newbie.

#-o

Hee hee. milli360 is much more than a Bad Grad. He has the most posts of anybody, but because he does not want to flaunt his superior posting skills, he graciously switches identities every kPi posts. (This also makes it harder for the FBI to find him.)

milli360

2004-Mar-26, 10:31 AM

because he does not want to flaunt his superior posting skills

I like that way of putting it

(This also makes it harder for the FBI to find him.)

But that's another way. (And the CIA and the NSA and the DSS and the NRO and Bino's Bail Bonds...)

pi is exactly 3

2004-Mar-26, 12:18 PM

what were milli360's previous names?

Glom

2004-Mar-26, 12:45 PM

what were milli360's previous names?

Grapes of Wrath and kilopi.

milli360

2004-Mar-26, 04:42 PM

They've been in my profile ever since.

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