Re: ISS Solar Transit

From: via Seesat-l <>
Date: 28 May 2014 10:26:44 -0700
Hello Debasis Sarkar,

You wrote:
"despite being on centerline (Plus Minus 200 meters), I did not get ISS to run through the center of solar disc. Instead, I had it pass through a distance of at least 1/4 solar radii from the center of Sun."

From your photos, I agree with your estimate: the path across the disk appears to be about 5 minutes of arc away from the center of the Sun. Given an altitude of 417 km, and 87 degrees high, almost straight up, this corresponds to a position offset on the ground of about 600 meters (that's 417km*5/3438). You say you believe your position was accurate to 200 meters. A difference of 600 meters is only moderately outside that limit. Is it possible you were 600 meters off the center line? Did you get your lat/lon from some GPS-equipped device at the time of the solar transit? If your position was instead taken from mapped data, like Google Earth or similar, there's a possibility of an offset that large. You wondered about an offset due to altitude above sea level. Since the ISS was nearly straight up, there would be no significant difference. Of course a slightly "stale" TLE is also a possibility, but there were no orbital adjustments around the time of your transit so this seem!
 s unlikely to me. Small errors in the prediction algorithms employed on the calsky site are also a possibility.

Frank Reed
Conanicut Island USA
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Received on Wed May 28 2014 - 17:26:44 UTC

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