ISS Lunar Transit

Since I was little kid, I have been attracted with astronomy things, like watching constellations and just learning what’s going on up there, so when I start with photography I one the first lens I bought was a cheap Opteka 650mm – 1300mm. It was incredible how far I could get with that I remember watching the moon for hours and hours, I was just so impressed with how close I was able to see the moon by myself.

One day, back in Venezuela February 21, 2011 , when I was in high school some people from some sort of astronomy class give us like a presentation and invited us that night to come and learn by our self how to watch things in the dark sky.

I remember having my camera with the big lens that night trying to watch stars and planets from the football field of my school , suddenly one of the professors said loud, look guys! Do you guys see that little yellow start moving very smooth and slow? I yell yes! I see it! What is that? He said to us, that’s The International Space Station, and there are a few astronauts working up there making research and experiments. I was really confused about that, like are there people living in the space ? I asked that too many times in my head that I couldn’t believe it . With the years I kind forget about the ISS itself , I knew there was a satellite going around us because I make a lot of research after that class , but I never paid too much attention to it because it was just impossible to my eyes see that thing going to fats around us , even with my big lens it would be impossible to see it in the dark sky, I could only see the yellow dot like it was a start .

Many have seen the International Space Station glide across the dark sky in the hours after sunset or before sunrise while it is still lit by the sun . For most locations, visible passes occur at least every few days and sometimes more than once per night. Several years ago , some clever folks at www.transit-finder.com created a way that anyone can enter their location and find a place near them where the ISS would appear to fly directly in front of the sun or the moon . When such a “transit” occurs, the path of visibility is very narrow… only a few miles at most . The timing is also very critical… orbiting at over 17,000 miles per hour , the ISS usually takes only one second or less to cross the moon or the sun . Attempting to photograph a transit can be done with minimal equipment and is a brilliant way to demonstrate the science of orbital mechanics.

The Transit-Finder website allows one to specify how far from their home they are willing to go to photograph a transit . It shows the path of visibility on a map or satellite view with the ability to zoom and move around to find a good location to set up. Try to pick a location in the center of the path for a transit that will cross over the center of the moon or the sun and for the longest transit time. A hundred yards, either way, make a definite difference, so be picky about your location. The data at the website is updated frequently due to small changes in the orbital path and altitude of the ISS , so check before you go to your chosen site to be sure that nothing has changed . I found that over the course of an afternoon the prime location for me and my partner’s latest attempt changed by about fifty yards and the time changed by one-tenth of a second.

A telescope is not required if you have a lens with a long enough focal length to make the moon or the sun occupy at least half of your field of view. Obviously, for the sun, a solar filter will be required. Generally, the apparent size of the ISS will be around one arc-minute, so it will appear to be about one-thirtieth of the diameter of the moon / sun . If your imaging scale is such that you have a small image of the moon / sun , then the ISS may not clearly be distinguishable . A 2X teleconverter may be helpful to increase your total focal length. For a DSLR that uses a crop-frame sensor (most consumer models), a focal length between 600 and 1000 mm would be desirable. For a full-frame DSLR, a bit longer focal length is required. A small refracting or Schmidt-Cassegrain telescope of the proper focal length is ideal for this.