Tonight there was another pretty good ISS pass over Los Angeles at 22:02 PDT.
I’ve talked several times about how tough it is to get a good picture of the ISS over Los Angeles because of all the light pollution here. I would like to use a really long exposure, up to three or four minutes, in order to catch the ISS’s arch across the sky. But that’s hard to do since anything over about 30 or 40 seconds gets washed out and very overexposed due to all of the street lights. Instead, I end up taking and posting a series of 20 or 30 second exposures and then just publishing the whole series.
Online I’ve noticed a number of folks who have very nice pictures of ISS passes, but the image from the ISS is broken up like a dashed line, not a solid line. Today I asked one of them about it and confirmed what I had suspected. They’re taking a whole series of much shorter pictures, then using software to combine them into one. In astronomy this is a common practice called “stacking,” which we’ll talk about a great deal more as I start to play with it.
I downloaded some freeware that was recommended (thanks, @Steve_P_Knight) and instead of one or two 30-second exposures, I shot a series of thirteen images, each 5 seconds long, with about a half-second delay between each image. I then combined them using software into a single image. Since the only thing moving in the picture was the ISS (and that 737 going into Burbank), the combined image looks like this:
It should be obvious which is the ISS and which is the 737.
This is a cool new thing to play with, a new tool in my amateur astrophotography toolkit.