The International Space Station (ISS) is around 248 miles above the earth, traveling at a speed of almost five miles per second, circling the earth every 92 minutes. The ISS will occasionally cross over the moon or sun. It goes too fast to see it with the naked eye, but with the right equipment and preparation, it's possible to photograph the ISS crossing the sun or moon.
www.transit-finder.com is key to knowing when and where the ISS is going to pass by the sun or moon.
Visit the website, select your location, and view the results for your region in the next month. I like to note any solar or lunar transits in the upcoming month that I'd be able to drive to, and then a week before, and the day before, check Transit Finder again to confirm that it's still happening at the same time and place. There have been transits I've found three weeks ahead of time that have shifted their time or location slightly as the day gets closer.
The day before the transit, I make sure the following is packed:
• Nikon Z7. The high-resolution makes it easier to see the ISS details as it goes past the moon.
• Memory card and fully-charged battery. It's way too easy to forget a memory card in the computer, or a battery in the charger, which would make the whole photography trip for naught.
• Nikon 500mm f/8 mirror lens. When it comes to sharpness and image quality, this lens is doesn't compare to other similar super-telephotos. What it does make up for is price and transportability. I purchased mine for around $150 from eBay, shipped from Japan. The Z7's focus peaking and live view functionality makes it usable for getting the moon in focus.
• Nikon 2x teleconverter. Another cheap pickup from eBay for around $50 shipped, this was one of Nikon's oldest versions from the 1950s or 60s, but does get the extra zoom to get the moon or sun larger in the frame.
• Tripod. The sturdier the better, I have an inexpensive travel tripod I use most of the time, but I'll keep the legs short to reduce camera shake.
•Remote shutter. The Nikon Z7 uses the Nikon MC-DC2. A remote shutter is useful to reduce camera shake when taking the photo. I personally prefer a wired remote for this to reduce possible failure points or latency with a wireless remote.
• Sky-Watcher Star Adventurer 2i. This isn't necessary for shooting the ISS transit, but if you already have one, or were considering one, it's helpful. This star tracker can track the movement of the moon or sun across the sky; this avoids needing to continuously adjust your tripod to keep the moon in frame; at 500mm and above, the moon moves quickly enough across the frame that you'll need to make sure it's in frame before the shot happens.
THE DAY OF
I drive out to the location to give myself about 30 minutes of time before the transit occurs to get plenty of time to get everything set up.
I'll set up my tripod, mount the Star Adventurer pointing roughly towards north, attach my camera and remote shutter, and then get the moon in frame.
I'll set my camera settings to shoot with an extremely fast shutter speed. My setup of a 500mm f/8 mirror lens, and a 50+ year-old teleconverter, means that I'm shooting at something like f/16. At 1/1000 sec, I still need to crank the ISO to 1000 in order to have a decently lit image. Using a more modern lens with a wider aperture would mean you could shoot faster (closer to 1/2000 sec) and with a lower aperture and ISO.
I like to re-check exactly how long my camera can shoot before the buffer fills - I'll point it at the moon, and fire shots until it stops, keeping track of how many seconds it runs. If it's ~10 seconds, this tells me to start firing photos five seconds before the transit occurs.
Every few minutes, I'll make sure the moon is still in the frame, adjusting as necessary.
I go back to transit-finder.com, and recheck the exact time that the ISS will pass the moon. To make sure I have the exact right time, I go to time.gov and watch the seconds tick by. As soon as I'm (in my case) about five seconds before the transit, I hit the shutter and let it run until the buffer fills.
After the moment passes, I go back through the frames and see if I caught the ISS! With some luck, and planning, you'll see a small, black dot moving across the frame. That's the International Space Station!