Introduction
The most challenging photo I have ever taken was the International Space Station (ISS) transiting the Moon. I failed four times before catching it on the fifth attempt. Once I successfully captured this photo, I took it to the Sun. This article is about what it takes to capture this photo. There is a lot of information in this post, necessarily, so bear with me until the end in order to get a complete picture, so to speak.
My method was utilizing gear a photographer might have, whereas a dedicated astrophotographer would be able to do this with less expensive gear but ultra-specialized equipment, which I can briefly cover as astrophotography is a hobby I’m beginning to ease into… but that isn’t what this post is about.
International Space Station transiting the Moon.
The equipment I use is equipment I have from hobby and semi-professional photography and is certainly more expensive than the cheapest options to successfully get this photo. This means if you are already a photographer, regardless of “level”, my setup might be the most practical for you. If you are just looking to get into this and don’t already have much equipment, or any at all, you might be better going with a dedicated astrophotography setup because it’s significantly less expensive. If you aren’t interested in touching on the dedicated astrophotography setup, skip the following paragraph:
While I take a lot of astro photos, I don’t have a dedicated astrophotography setup, yet. I studied aerospace engineering and have a beginners understanding of dedicated astrophotography setups but no practical experience. Long story short, you can purchase a used “dobsonian telescope” for a couple hundred dollars, a used dslr camera for a couple hundreds dollars, an adapter for the camera to the telescope, and then use details from the rest of this post and your practice and proficiency with your setup.
Gear
I would also like to acknowledge that there are non-dedicated astrophotography setups plenty less expensive compared to my setup, but you will still need quite a long lens and a camera with rapid shooting.
My complete setup includes the following:
Marumi ND100000 77mm Solar Filter (only for the Sun)
Laptop + camera to computer cable + Canon EOS Utility Remote Software Free
Smart Phone
Small foam pad (to keep your butt warm)
Here is a mock-up for what my general setup looks like.
Before we get into how exactly you get a photo of the ISS transiting the Moon, we need to make sure you're already proficient at obtaining quality, consistent photos of the Moon without the ISS. I wrote a comprehensive article on how to do this, which you find by clicking this sentence. An element of that post is how to stack photos to make a more resolute image. That isn’t entirely relevant here other than the fact it emphasizes the importance of being confident in taking a great photo of the Moon, which will be necessary to get a great photo of the ISS transiting the Moon.
I won’t talk much about how to get a quality photo of the Moon, that is a prerequisite to attempting a photograph of the ISS transiting the Moon. However, in this particular case, your camera will be firing at a high-speed with a very fast shutter-speed simply because the ISS travels five miles every second, that’s crossing the Atlantic Ocean in as short as six minutes and as long as nine minutes, depending on the location. So, out of necessity, you’ll need to be able to get consistent, quality photos of the Moon shooting at a couple thousandths of a second. And you’ll need to be able to do it in various Moon phases because it’s out of your control when and where the ISS will transit the Moon.
Technical Details
Once mastering photographing the Moon, how do you know when and where the International Space Station will transit the Moon? The easiest way to figure this out is to use the website Transit Finder.
All it takes is to plug in your coordinates and hit “calculate”. The results are listed by date so you know when in the future the transit is. It lists both Lunar and Solar transits and then gives a star rating for each transit based on the state of the transit. Rather than try and explain here, on the Transit Finder website, click “How to use this website”. You will learn a lot about transits and I highly recommend reading it.
Because the International Space Station has a 90 minute day, orbiting Earth about sixteen times in twenty-four hours, you could theoretically have multiple opportunities per day, everyday, to try and get this photo. That’s impossible, realistically speaking. There is a very narrow band of land that you need to take the photo from in order to see the transit, so you’d have to drive hundreds of miles to try and get into the same band when the ISS comes back around the Earth to pass over you and under the Moon again. That’s the reason (among others) it took me a few months and a few attempts to capture the photo.
There are a handful of variables that you need to attempt to control in order to get the shot:
Weather
Weather is clearly the obvious one but the list wouldn’t be complete without talking about it. Other than clouds covering the Moon, pollution also makes a difference. In astronomy and astrophotography light pollution is a big problem. But that doesn’t really matter when photographing the Moon. What matters is any haze that will distort and soften details on the Moon, but especially the ISS. The ISS is so small against the Moon that even if your photo is tack sharp, you could lose a little detail in the ISS due to haze. The only way to manage this variable is to go to a location on the band of transit that is further away from a city or major highway.
Altitude
The further away the Moon is from the horizon, the better. While transit time is longer closer to the horizon (giving you better odds), atmospheric disturbance will soften or blur your image even if you’ve checked all other boxes. You’re taking a photo through far more atmosphere than you would when the Moon is higher in altitude, which is something to look for when evaluating the Transit Finder website. Your photo will be of higher quality the further the Moon is from the horizon.
Time of Transit
This was hard for me to figure out and is definitely the most challenging. The words I would use are, “timing your shot”. Lets say you have a single shot camera and you watch the ISS rise in the horizon at 17,000 mph towards the Moon, and then you need to snap the shot in the window that it transits the Moon. That might as well be impossible.
The Transit Finder website will tell you the time of transit to the hundredth of a second, which changes depending on your location. You need to know exactly what your coordinates will be when you take the photo because those coordinates are used by the website to tell you the moment of transit. If you’re even a couple miles down the band of transit, the time will be off. What also happens is this specific time will slightly change over the weeks and days as calculations become more precise. If the transit lasts 0.64 seconds (like in my above photo), being off by 1 second will make you miss it. That previous number, 0.64 seconds, usually shocks people because of how fast that is. As mentioned in the previous paragraph, the lower the Moon is in the horizon, the longer the transit, but also the worse the photo. If the Moon is sitting on the horizon, the transit duration will be several seconds but the quality will be low. So timing your shot perfectly is critical to get a photo with the Moon at a higher altitude, but you’ll be rewarded with a higher quality photo.
The sneaky thing that I completely missed was knowing that the clock on your phone has a network latency, and it’s different for every phone, carrier, and cell tower. The International Space Station operates on the official atomic clock. This is why I include my smart phone as a piece of gear. My phone’s latency according to the atomic clock was +1.260 seconds… when you have a transit duration of 0.64 seconds, you might as well stay home or get lucky when you shouldn’t. As I write this my desktop latency is +0.254 seconds. Your transit time needs to be based on the atomic clock and adjusted for network latency, which the previous linked page does for you.
Location
I already wrote a few things about this but I’ll put it all together here. When you select a transit that’s near you, the Transit Finder website will show you a map along with an overlay of the band of transit. You’ll be quite lucky to live within that transit’s band so you’ll almost always need to drive to a location. You’ll want to get as close to the center of that band as possible because that means the ISS will pass through the middle of the Moon, giving you the longest window of time for that specific transit. You’ll notice in my top photo that I was quite close to the center of the band but not perfect. If you’re on the very edge of the band then the ISS will barely touch the Moon and the timing of your photo will be a couple hundredths of a second long, good luck.
If you’re not already intimate with a great location along this band, you’ll probably want to scout it out or give yourself a good amount of time beforehand to find a spot. You’ll obviously want it to be public land in an area that isn’t dangerous to you, like the side of a road. You might be able to get away with private land if it’s, say, in a large parking lot at night. You should already know to be on pavement/cement if you are proficient at taking photos of the Moon (start here if you’re not). I usually do scouting on “street view” in Google Maps or Google Earth.
Also, avoid people as much as possible; They will come up and ask what you’re doing, which is a major break of focus.
Transit-Finder example at the base of Mt. Rainier in Washington state. The altitude of the Moon is low to the horizon so the transit duration quite high at 2.48 seconds. The pinned location isn’t on the center line so the line of transit shifted, making your window of opportunity less.
Camera Settings
If you have practiced photographing the Moon and are quite proficient at it, this section won’t be too unique. I can’t stress enough, you need to already take great photos of the Moon. Because the ISS is traveling so fast, your shutter-speed must be as high as possible. There is no true rule to this but I personally aim for at least 3 times the length of my lens. I’m at 400mm so I try to at least go for 1/1200th of a second. Achieving a shutter-speed well above concern is generally easy. If your aperture isn’t as open as possible, then it should be as close to it’s optimal sharpness as possible without dropping below a safe shutter-speed (see the previous link above and search the page for “optimal sharpness”). The brighter the Moon, the easier this is. Keep the ISO as low as possible and only begin to increase it if you absolutely have to in order to get your shutter-speed high enough. Even if you slightly under-expose the image to keep that shutter-speed high, you can go into your post-processing afterwards and raise the exposure level. Keep that shutter-speed high!
Also make sure you’re set to your camera’s high-speed mode so that it’ll shoot as many photos as possible during the transit. My camera shoots about 7 photos per second so with a 0.64 second transit when dead center on the band, that’s only a few photos in transit if I time it perfectly. Given the files are in RAW format, I can shoot about 20 high-speed before my camera lags due to writing speed on the memory card. So I’ll start shooting about 1 second before transit until about 1 second after transit. That gives me about 20 photos in a window of about 3 seconds to catch the transit window that’s likely less than 1 second, if that makes sense. So long as the transit happens inside my window, then I should have a few photos with the ISS in transit or better odds of at least 1 photo if I slightly miss the perfect window.
Post-Processing
I won’t spend much time here because every person has their preferred software and you likely already know how to use it for the Moon. I use Lightroom for just about everything and then I take it from Lightroom into Photoshop if I need to. What I will say is that if you did capture a few photos of the ISS transiting the Moon, then you can merge them into a single photo that shows it’s travel path, like my top photo. You don’t need to, but it’s an option.
Congratulations if you got the photo! It’s a real challenge that requires a lot of focus and it’s a photo that not many people get.
International Space Station - Solar Transit
Now that you’ve successfully achieved the ISS transiting the Moon, why not try it with the Sun? The Transit-Finder website shows those transits as well, it just requires an extra, critical step to make it happen. A solar filter. DO NOT POINT YOUR CAMERA AT THE SUN WITHOUT A SOLAR FILTER! YOU WILL GO BLIND! And if you do it in on your camera’s LCD screen, you will destroy your sensor. The filter needs to be specifically for the Sun. This isn’t an ND10 filter, it’s an ND100000 filter, or something similar. This costs some money for such a specific photo but it’s that much more unique.
International Space Station - Solar Transit
Thank’s for making it to the end :)