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*Subject*: RE: [amsat-bb] AO40 velocity*From*: "Vince Fiscus, KB7ADL" <vlfiscus@xxxxxxx>*Date*: Thu, 29 Aug 2002 21:26:58 -0600*In-Reply-To*: <000501c24fc5$1fa58cd0$0200a8c0@tomcat>

I think what he wanted to know is what is the magnitude of the velocity vector, and an equations to calculate it at any point in the orbit. At 09:32 PM 8/29/02 -0400, <w3iwi@toad.net> wrote: >Margaret is correct in stating that the reference frame needs to be defined. >The answer that Stacey (W4SM) gave applied to an observer at the center of >the earth. > >Let me expand on this with a couple of simple examples (which also give you >some fun "magic numbers" to help the next time you have to answer these >questions in a dingy bar): > > ----------------------------------------- > >The earth rotates on its axis every 24 hours = 86400 seconds. The original >definition of the meter is that 10,000,000 meters is the distance from pole >to equator along the meridian of Paris. Therefore I can take this number >(and ignoring the fact that the earth is flattened), I immediately know that >the circumference of the earth is 40,000 km. > >So if you are an observer on the equator, you are spinning at a speed of >40000/86400 = 463 meters/second. If you are at a higher latitude, then your >spin velocity is reduced by cosine(latitude), so at 40 degrees (like >Boulder), you are moving at 355 meters/second. So if the 'how fast "those >things" go' question is answered for an observer on the earth you need to >account for this effect, which is ~5% of the speeds that Stacey gave. > > ----------------------------------------- > >Now lets move the observer into interstellar space (perhaps at Alpha >Centauri). The earth's distance from the sun (one AU = Astronomical Unit) is >about 150,000,000 km and the earth's orbit is nearly circular, so the >circumference of the orbit is 2*pi*150,000,000 km. The earth goes around the >sun in one year which just happens to be pi*10,000,000 seconds (to within a >small fraction of a percent) > >So the earth's orbital velocity can add as much 30 km/sec for part of the >year and subtract 30 km/sec 6 months later when seen from outside. This is >nearly 4 times the speeds that Stacey answered. > > > >Define the observer -- It's all relative! > >73, de Tom, W3IWI > > > >---- >Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA. >To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org ---- Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA. To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org

**References**:**Re: AO40 velocity***From:*Margaret Leber

**RE: AO40 velocity***From:*Tom Clark, W3IWI

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