October 24, 2019 ~ Two weeks before this, I was ending my day in Anahuac National Wildlife Refuge on the Shoveler Pond Boardwalk, using the last of the twilight to photograph birds flying overhead to their nesting spot in the marshes north of the walking pier.
On a whim, I aimed at the moon just rising in the early night sky. The moon is over one quarter of a million miles away, and measured straight across, like a dinner plate, it is 2000 miles wide. But it’s not a dinner plate, it is a sphere. So, would I need a deep or shallow depth of field? For any specific f-stop rating, the depth of field is shallower for objects close to you, and deeper for objects farther away. I reasoned that my shallowest depth of field, f5.6, would probably be ok, since that quarter of a million miles was a YUGE distance, and it seemed likely I would get the whole spherical body in focus.
Since the autofocus system on my Nikon D850 uses visual contrast to find and focus sharply on objects, I aimed at the fully lit edge of the moon, rather than at the dawn/dusk transition line where the sun’s light didn’t cover the full face of the moon. I was tickled with the deep indigo blue of the sky, and the highlighted crater edges along the transition line.
But that made me wonder what other photographic opportunities the moon might provide.
I turned to one of my favorite apps, which is also a website, called ISS Transit Finder. This app calculates the dates and times that the International Space Station will be passing near, or in front of, the Sun or the Moon, when viewed from specific locations around the world. Sure enough, I saw an opportunity coming up two weeks later. The International Space, fully lit by the sun and sparkling in the black night sky, would cross the dark face of the crescent moon, on October 24, 2019, at 5:58am, when observed from a path that passed through Dime Box, Texas. Whew! That is a lot of facts to include in a calculation. But the app makes it easy to find these opportunities.
I invited my husband and an astronomer friend to join me on this field trip. We carried the map of the transit path with us, and spent the day before the transit searching between Upton and Dime Box for a place where the transit viewing path crossed a road, and the road had a good place to pull the truck over safely and room to set up my camera and my friend’s telescope. OH. And the place needed to have no telephone poles or wires to the east, no city lights over the eastern horizon, and no farm lights shining in our eyes at night. And we needed to pray that the clear skies held. Not so much to ask, now is it?
At 4:30am the next morning, we bundled up against the chill breeze, slogged out of the hotel with questionable coffee in hand, and drove to our chosen small gravel county road with a turnout at the entrance to a closed down gas pumping well. We set up, groaning as wispy clouds shadowed the face of the moon, and then quietly counted down the seconds until the Station’s appearance low on the southeastern horizon. The Station would be in view for two full minutes, but would cross the face of the moon in only 1.19 seconds. That’s “One-thou-sand-one, One-“. To catch the image, I would use the “Continuous High Speed”, or “CH” shutter release mode, firing 6 frames per second.
Remember my logic for shooting the moon from Anahuac using f/5.6? Well, I was presented with a problem here. The moon is one quarter of a million miles away… and the Station is only 250 miles above the earth. My depth of field would need to cover an astounding 124,000 miles. Ideally, I should have shot with the highest f-stop available on my lens, f/32. Of course, that would have required an enormous ISO setting… and I have no experience pushing the camera to those extremes. I’ll save that experiment for another transit. I chose f/8 to increase the depth of field a bit while staying within the limits of the 1/1000 shutter speed.
The Station is approximately as big as a Boeing 747 jetliner. Jets on long trips typically fly five to six miles above the earth. I was trying to photograph a vessel as big as an aircraft, but 500 times further away. I’m amazed that I captured the hint of its solar panel “wings” at such a distance.
As the Station sailed past the moon, the wispy clouds cleared, and I got one clear shot of the shining face of the moon. It was a wonderful photo experience that started with an ibis flyover, and ended with the ISS flyover.