Saturday, July 15, 2017

International Space Station

If you are in the right place at the right time you might be able to catch a glimpse of the International Space Station (ISS) as it passes in front of the Sun or Moon. These types of events are called "transits" and are fairly uncommon.

Transits are hard to see and easy to miss. The ISS orbits between 205 and 255 miles above the surface of the Earth, and moves at over 17,000 miles per hour. At that distance and speed, lunar and solar transits only last about one second or less and are only visible from a relatively narrow strip of land on the Earth's surface.

But finding a good viewing spot and time is relatively easy with ISS Transit Finder. This site lets you specify an area and a date range, and will calculate when and where the ISS will pass in front of the Sun or Moon.

A solar transit occurred on July 14, 2017. The center of the centerline of the transit was located in Lake Raven in Huntsville State Park, which is not far from where I live. I set up the ShortTube 80 with a full-aperture glass solar filter along the shore of the lake, and caught the transit using the Mallincam SkyRaider camera. Here is a composite image of the transit:

International Space Station transit of the Sun, July 14, 2017. Sunspot group AR2665 is located on the right.

The frame rate of the camera was not consistent, which is why there are gaps in the image sequence. The original monochrome images have been colorized to approximate the view through the solar filter.

The following video shows the transit in fairly close to real-time. Note that there are TWO transits! The first is probably an insect that either flew in front of the telescope or crawled across the objective lens.

On a side note, one of the lessons that I learned from the Venus Transit was that good polar alignment is critical for good results. This is difficult to do in the daytime, though, unless the mount has some kind of "magic" hardware and software for figuring out its exact position. My '80s-tech Vixen Super Polaris EQ mount does not have any fancy alignment features, but I was able to get a decent polar alignment using my mobile phone.

I plan on trying to image more ISS transits in the future when the opportunities arise. I would really like to get a lunar transit now.

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