[Chaos-l] ISS Lunar transit

[Joe Pedit]

I've used the ISS predictions available on CalSky on a few occasions to 
image the ISS as it has passed in front of the moon and sun.  The 
prediction times given by CalSky are local times (i.e., Eastern Standard 
Time in the winter).  The orbital elements used to predict the transits 
are updated frequently so the most accurate predictions are usually 
available within a day of the transit of interest.  While the 
predictions are quite good, they are by no means perfect.  For example, 
the predicted path width for the first transit I imaged was 4.5 
kilometers.  I was only 100 meters from the predicted center line, yet 
the resulting image (http://www.unc.edu/~pedit/astro/iss_lunar_50.html) 
showed that I must have been much further from the actual center line 
than that predicted by CalSky.

The duration of the ISS transits can be as short as 0.4 seconds when the 
moon or sun are directly overhead (altitude of 90 degrees) to about two 
seconds when the moon or sun are only 15 to 20 degrees above the 
horizon.  Similarly, the angular size of the ISS can be as large as 54 
arc seconds when the moon or sun are directly overhead to about 20 arc 
seconds when the moon or sun are only 15 to 20 degrees above the horizon.

Daytime transits of the moon may or may not be visible depending on 
whether the ISS is illuminated by the sun.  CalSky will usually provide 
this information.  The December 1st transit occurs when the moon is only 
17.2 degrees above the horizon so it has a very forgiving 15.2 km path 
width (i.e., you only have to be within 7.6 kilometers of the predicted 
center line).  The predicted duration is pleasantly long at 1.32 
seconds, but only a small fraction of that occurs when the ISS is in 
front of the illuminated portion of the moon.

Joe

P.S.  A 15 second movie that covers 166 minutes of the Morehead 
observing session held on November 13th can be found at the links given 
below.

720 x 480 pixels, 5.1 megabytes
http://www.unc.edu/~pedit/720_480_337.html

480 x 320 pixels, 1.0 megabytes
http://www.unc.edu/~pedit/480_320_337.html

The movie file has to fully load before play begins.


On 11/26/2010 12:56 PM, walter fowler wrote:
> Joe, Is this still your e-mail address?  Are you still on the CHAOS 
> listserve?  It seems very confusing as to when the ISS is going to 
> cross the lunar disk although the map below shows that it should be 
> right over my house.   Jim Pressley said that you took some photos of 
> the ISS crossing the solar disk and that you would be the one who 
> could clear up the confusion.  It would be great if you would put up 
> one of your photos of the CHAOS listserve as well since it's a matter 
> of interest right now.  Thanks and Happy Thanksgiving.  Walter
>
> ---------- Forwarded message ----------
> From: *Tony Rice* <rtphokie at gmail.com <mailto:rtphokie at gmail.com>>
> Date: Tue, Nov 23, 2010 at 5:57 PM
> Subject: Re: [Chaos-l] ISS Lunar transit
> To: Robert Nielsen <robertnielsen at nc.rr.com 
> <mailto:robertnielsen at nc.rr.com>>, raleighastro at yahoogroups.com 
> <mailto:raleighastro at yahoogroups.com>, CHAOS <chaos-l at rtpnet.org 
> <mailto:chaos-l at rtpnet.org>>
> Cc: "mark63clegg at aol.com <mailto:mark63clegg at aol.com>" 
> <mark63clegg at aol.com <mailto:mark63clegg at aol.com>>
>
>
> Thanks for catching that.  I'd forgotten that I'd set the search to 2
> weeks.  The visibile transit is indeed Dec 1.
>
> http://www.calsky.com/?Transitline=&obs=54404012470422&tdt=2455532.22692995&sat=25544&interval=0.00011574&step=0.00000231&mainbody=10 
> <http://www.calsky.com/?Transitline=&obs=54404012470422&tdt=2455532.22692995&sat=25544&interval=0.00011574&step=0.00000231&mainbody=10>
>
> -Tony
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