Wednesday, July 27, 2016

The ISS flies over the moon

Oops, I did that again! After almost 19 months I was able to take again a video of the ISS passing the moon! (Here is the story of the first time I caught the ISS and the moon).

I am receiving alerts from calsky site about satellites crossing the moon, but I usually ignore them since most of the time it is a very small satellite which requires telescopes and to find the exact place, but this alert was different.

What are the chances to see an ISS pass? Very high, it happens all the time. what are the chances that the ISS will cross the moon? I think that *somewhere* it also happens all the time. But what are the chances that the crossing will happen exactly at your house?? Ohm. Small, rather small.
But improbable things happens all the times and as I got the alert I checked the predictions (see the appendix) and saw that indeed all I need to do is to go outside to my roof.

Even the problematic hour 4:56am did not bother me. I decided for the best configuration for my equipment and made all setups I could the evening before. I set an alarm and went to sleep early.

Getting up at 4:15 the skies are full of clouds, ignored them and continue to setup the system. Clouds come and goes and there is plenty of time, so just hope for the best. I aligned the mount and put my 70mm doublet on it with Canon700d on video mode.

I use a Nikon 900P camera with a mighty zoom on a regular tripod without tracking and an old Canon SX30 for backup. Ten minutes before the pass and everything was entirely cloudy. Five minutes before the pass the sky was clear.

Waiting. Here it is! Above the moon and going down so quick. Fast. Press record here, here and here! make a last alignment for the non-tracked Nikon camera and wait.

I took  a look at the eyefinder to see if it catches the ISS but saw nothing. I looked at the ISS and saw that it already passed the moon. Well maybe the predictions were no that accurate and it missed the moon in a degree that is possible, nothing to do about that. Turn off all recordings, take apart everything I can without making too much noise (5am in the morning) and check what happened on the computer.

Happily, I found out that all three cameras captured the ISS. Most of the pass was on the dark side of the moon and only a fraction of it on the lit side. Here are the results combined into a single view. Please look at it on full screen with HD resolution

I tried to extract a single image from the video but the ISS was too smudged. I think that The Nikon camera went back to its default 30fps and not to the 60fps I set it up before. Always check your setup again, even if you are too tired at 4am! The ISS is the white little line on the dark side of the moon.

The ISS flies over the moon
The ISS flies over the moon

Some hints and tips for the next time
One problem of such videos/photos is that it is hard to practice. The duration of the pass is one second or less. My recommendations for the next time are:
  1. Take the highest FPS you can: 60 120 or even 240 (with iPhone aligned to the eyepiece)
  2. Practice on a regular moon without the ISS
  3. To freeze the ISS use 1/1600 shutter speed
  4. If you have a DSLR with a high zoom lens, use burst mode and don't take video.
  5. Have fun doing all of that! 
Appendix: Check predictions in Heavens-Above
Heavens-Above is a great site to get information about ISS and other passes. Try it out, it is simple and intuitive.
When selecting a pass you see a general map of it. Vawalla! The pass is on the moon!

Heavens-Above prediction of the pass - regaulr
Heavens-Above prediction of the pass - regular

This is not certain tough and you must press the map to get t magnify. If in the magnified map the pass is on the moon, you can start preparing your gear, but take into account that as it implies, these maps are predictions only.

Heavens-Above prediction of the pass - magnified
Heavens-Above prediction of the pass - magnified