Rob Matson's SkyMap (and other graphic programs with accurate shadow computation?) will easily give you position and size (diameter, or the chord that the geo belt traverses on a given date) To get km, move the crosshair to a geo belt sat, press T to read the range, then multiply by 2*tan(width/2). See http://www.algonet.se/~b_gimle/geoflare.htm and the its first image (http://www.algonet.se/~b_gimle/gif/Geo_NL.gif) and the .cfg file I used to construct it : http://www.algonet.se/~b_gimle/gif/GEO_NL. CFG Actually, since the chart shows satellites during a <= 30 min interval, and the shadow appears to move by about 2 degrees per hour, it does appear about 1 degree wider than it is. >----Ursprungligt meddelande---- >Från: john@satcom.freeserve.co.uk >Datum: Oct 10, 2004 2:01:59 PM >Till: SeeSat-L@satobs.org >Ärende: Earth shadow radius > >Hi all, > > >Jeff recently asked about the radius of earth shadow , as cast on the geo >arc , under perfect conditions. > >For my location , here in the UK , I should be able to get an accurate >"guesstimate" ... if there is such a thing , by observing the track of earth >shadow this evening....the peak of the eclipse/outage season for this >latitude. >However , as I seem to be clouded in again , its highly unlikely that I will >get the opportunity. > > >Looking at the video timings from the other night , I can see that the >leading edge of the shadow was moving at a rate of one degree every 3.5 >minutes or so , which is about right....and as the satellites at 28.5 >degrees were coming out of eclipse , the birds at 16 east were just >entering. >So , this gives a shadow diameter of 12.5 degrees. >Converting this to km , I get a figure of 9250km. >I would expect this figure to be in excess of 12,800 km tonight , when >everything is lined up . > >Does this seem right ? >I'd appreciate any comments from more proficient math students ;O) > >The video has also revealed that the geos in orbit over Europe are now >increasing in magnitude , just prior to eclipse , to a level of mag 8 or >better , bringing them into bino range. >This became apparent when I started to examine the dropped frames from >friday's recordings. > > >Regards, > >John. > > > >------------------------------------------------------------------------- >Subscribe/Unsubscribe info, Frequently Asked Questions, SeeSat-L archive: >http://www.satobs.org/seesat/seesatindex.html > > ------------------------------------------------------------------------- Subscribe/Unsubscribe info, Frequently Asked Questions, SeeSat-L archive: http://www.satobs.org/seesat/seesatindex.html
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