ISS Transit Over the Moon
Plan:
- I've written this for a presentation on 9/24/2020, expect different results if you're reading this later.
- You shouldn't really need to take notes, you can access mine on our club website, on the Past Meetings tab.
- Show google maps of Glen's house
- Right-click his house, pick "what's here", click on GPS coordinates, select them along the left edge of the screen, and copy to clipboard with Ctrl-C (Windows).
- Paste into transit-finder.com and delete last digit since transit-finder.com can't deal with too many digits of precision.
- Click the "Calculate" button and look at the results. These are the times the ISS will cross the Moon and Sun during the next 30 days from the location you've entered.
- Warning: Ignore the solar transits and solar close passes unless you're absolutely sure that you have safe solar filtration. You can damage your vision looking through an optical viewfinder, and you can damage your camera's sensor without proper filtration.
- Scroll down through the transit-finder results to the transit over the full moon on Wednesday 9/30 22:09:21.06
- Note this is a 1.6-second-long transit -- the ISS will cross in front of the moon over a 1.6-second period of time.
- This is quite long because ISS is 800 km away (my solar transit was only 0.6 seconds because ISS was only 480km away)
- Altitude of the moon during the crossing is 28-degrees above horizon, azimuth = 130 = southeast (azimuth is measured by astronomers using 0=north, 90=east, 180=south, 270=west)
- Use street-view to check southeast horizon to be sure this will be visible from this site. You can also measure 28-degrees with your hands held out at arm's length.
An example if your house is not in the path of transit visiblity
- Google Map another house
- Paste coordinates into transit-finder.com
- See it's a near-miss on September 30
- Find a safe spot close to the centerline (Shelby Twp Fire Station #5, on Schoenherr, north of 21 mile road)
- Click the map on the parking lot behind the fire station and pick "Recalculate for this location".
- Notice that we're only 0.2 km off the centerline, the transit lasts 1.65 seconds. This is a good spot.
- Note that the time is 0.04 seconds later than Glen's house, 3.5 miles away as the crow flies. The ISS moves really quickly.
- The rest of this presentation revert's back to the circumstances at Glen's house
Equipment Requirements and Preparation:
- You need to use a Tripod
- You need to use a remote shutter release (either wired or wireless)
- Continuous shutter - measure now, with a stopwatch, how long you get between beginning to hold down the remote shutter release, and when camera slows down.
- Let's say that's 3 seconds
- So 3 seconds minus 1.6 seconds (the duration of the transit) = 1.4 seconds. So plan to begin shooting 0.7 seconds before the transit begins, and continue shooting until 0.7 seconds after the transit ends, to allow for errors.
- Therefore, on the night, you should begin holding down remote shutter release at 22:09:21.06 - 0.7 seconds = 22:09:20.36
- Write this time down in BIG NUMBERS, with a THICK BLACK MAGIC MARKER, in the bottom third of a WHITE PIECE OF PAPER: 10:09:20.36 PM
- How will you determine when it's that time? Download an Atomic Clock app onto your phone. On my iPhone, the app I use is named "Atomic Clock". I'm sure you can find a similar app for Android or whatever.
- Another thing you need to prepare for is the Manual Exposure you'll be using.
- If you've shot a full moon in the past at 1/200th or faster shutter speed, and are happy with the exposure, use those exposure settings.
- If you've not, then shoot the moon on Monday or Tuesday night as an experiment. I'd suggest starting with ISO 100, f/5.6, 1/120 sec.
- Expose properly for the moon, and the ISS will be a silhouette in front of the moon.
- You'd like to keep the exposure to 1/120 sec or maybe even faster, so the ISS is sharp rather than motion-blurred.
- When you determine the proper exposure, write the three settings (ISO, Aperture, Shutter Speed) down in BIG NUMBERS, with a THICK BLACK MAGIC MARKER, on the top third of your WHITE PAPER.
- The earth is rotating, causing the moon to move 1 degree every four minutes.
- A 500mm lens, full-frame-equivalent, captures a field of about 4-degrees by 3-degrees.
- The moon is 1/2 degree in diameter, so the field of view with the entire moon in the frame is 3-degrees by 2-degrees, therefore 12 minutes of time by 8 minutes of time.
- You'd ideally like the moon to be centered in your frame near the critical 1.6 seconds.
- So if using a 500mm full-frame-equivalent lens (333mm crop sensor, 250mm micro 4/3 sensor), you want the moon to be at the edge of the frame 6 minutes before the critical time.
- So in BIG NUMBERS, with a THICK BLACK MAGIC MARKER, on the center of your WHITE PAPER, write 10:03:20 PM (that's 10:09:20 minus 6 minutes). This is the time you'll need to lock down your tripod with the entire moon completely visible at the edge of the field, such that it will drift to the center 6 minutes later.
- This all assumes that you orient your camera so that the moon is moving across the center of the long edge of your camera frames. Be careful not to simply level your camera because this poor orientation might result. Instead you want this good orientation.
How to shoot, on the night of the event:
- Re-check transit-finder.com (the ISS orbit was adjusted just yesterday to avoid collision with space debris, changing this presentation a bit, and this can happen again at any time)
- Check whether it will be clear or cloudy. If solid clouds, pick a different day.
- Go outside 30 minutes before the event at 9:30 or 9:40, and setup your camera on your tripod with your remote shutter release
- Be sure to bring your smart phone and your WHITE PIECE OF PAPER outside with you. If you can't easily read your paper, bring a flashlight.
- Set your camera to Manual Exposure, Manual Focus, Continuous Sutter. Turn off stabilization if your camera is better on a tripod without it.
- Dial-in the exposure you've determined is correct, according to the top part of your WHITE PAPER.
- Use Live View (if mirrorless camera, you're _always_ in live view so don't worry about it) and focus on the moon.
- To focus astronomical objects, you'll be focusing your lens near the Infinity position.
- Magnify your live view as much as you can, and rotate focus back and forth, finding the spot where details on the moon are sharpest.
- Go too far to the left as you lose focus, the too far to the right as you lose focus by the same amount, then back to the center of those extremes.
- Take test shots to check whether your focus is accurate.
- Take your time to do this correctly.
- Once you know the focus is right, don't touch it again. Ever (unless the temperature changes significantly). And don't touch your exposure settings. Ever.
- Adjust your tripod so the camera is at a good orientation angle. Just watch how the moon drifts for a few minutes to learn how to angle your camera.
- Open your atomic clock app, when the time matches the time in the MIDDLE OF YOUR WHITE PIECE OF PAPER, put the moon at the edge of the frame (still at the correct angle) and lock your tripod down.
- When your atomic clock app shows the time you've written at the BOTTOM OF YOUR WHITE PIECE OF PAPER, Begin holding down your remote shutter button.
- When your camera buffer fills, and it slows down, you might as well release the remote shutter button. Either you planned, calculated, and executed everything correctly or you didn't.
Post-Processing:
- Import the photos into Lightroom, and have a look at them.
- I hope you can see the Moon in perfect focus on your images, and a small silhouette of the International Space Station (ISS) on them.
- Remember that we don't really expect to see the ISS on the first few photos, since we added 0.7 seconds of slack to the beginning in case our timing was wrong.
- Select all the images which indeed show the ISS passing over the moon.
- Right click one of them and select Edit In --> Open as Layers in Photoshop.
- I _think_ that for each layer above the bottom layer, you can simply add a Layer Mask, set to Black, and add a small white spot placed over the ISS on that layer. (show my solar photo in photoshop)
- If this doesn't look right (for example, a crater behind the ISS is misaligned due to the moon's motion), you might need to use Transform on each layer, to align the moon onto the layer below.
If your first attempt does not get the results you want, try, try, try again. This is not your only chance. The ISS will continue to drift across the moon every once in a while, perhaps with even better circumstances, as you take advantage of the lessons learned during this first attempt.