Monday, August 27, 2012

ISS Syzygy

Occasionally I check the Heavens-Above website - they are a nice clearinghouse of astronomy and satellite information.  I've blogged a time or two about the International Space Station's appearances in the sky - in fact, a little under 2 years ago, I observed it passing by the globular star cluster Messier 13.  I happened to notice a couple days go it would pass it again tonight - this time I'd be ready with a little longer focal length to show some cluster detail!  Of course, the space station can also appear next to, or even in front of the moon or sun!  Tom Polakis up in Phoenix, and others, use a program called Calsky to calculate where they need to be to see these.  Tom has a nice collection of these images that are fun to check out.

But for those starting out, Heavens-Above couldn't be much easier to use!  First you have to inform it where you live.  This can be done a number of ways - entering the country and town where you reside will work alright, though when you live in a large metropolitan area, you need to be a little more precise.  For some observations, such as for Iridium Flares, your position needs to be accurate to less than a kilometer (half mile) or so.  In that case, if you enter your town in the database, you can then click the Google Maps option to fine tune your position.  Make sure your time zone is entered properly too, otherwise you might miss it if you entered Mountain Time, but not Arizona, which does not observe Daylight Savings Time!  You would likely be off by an hour and miss the observation!

When you click on the ISS link, it brings up the dates it can be seen - clicking on the date in question brings up a full-sky map like that above which shows where it will appear in the sky.  On the bottom of the page it will show a close-up view, like this one of tonight's appearance, with tick marks for the time it will pass.  Tonight's was passing the "keystone" of Hercules about 20:15, so about an hour early, I set up the G-11 tracking mount with the little Meade 80mm F/6 APO refractor (480mm focal length).  I also set up a 200mm lens with a second camera, but ended up not using that image.

Right on time, the Space Station appeared to the left of the Big Dipper low in the northwest.  It was quite bright, predicted to be about -3.3, about midway between Jupiter and Venus in brightness.  I waited until it was about to enter Hercules, and started both Canon cameras with a 30 second exposure as it passed the cluster.  Shooting from town at F/6 and ISO 800 was about right for the sky brightness (a bright moon graced the sky too).  The image shows the cluster well, the streak of ISS overexposed.  Interestingly ISS, if examined in a telescope, is quite large, and the width of the streak is not merely due to overexposure, but to the large size of the structure.  You can barely see in the stretched image that the outer edge of the trail is not overexposed, denoting outer structures in the trail...  Another thing to note in the image, at about the 11 O'clock position between the globular and upper edge of the frame is a faint smudge - the galaxy NGC 6207 shows up in the 30 second exposure.  Well known to amateurs who examine M-13, it even showed up from town.
I'll keep looking for satellite conjunctions - I invite you to do the same!

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