Eye on the sky

Gary Hart Photography: High Sierra Moonrise, Glacier Point, Yosemite

High Sierra Moonrise, Glacier Point, Yosemite
Sony a7R II
Sony/Zeiss 24-70 f4
2.5 seconds
F/10
ISO 200

I spend much of my photography time chasing the moon. Most of my trips factor in the moon’s phase and location—usually to catch a full or crescent moon rising or setting above a particular landmark, and often to photograph a landscape by moonlight (full moon) or starlight (no moon). But sometimes the moon catches me less than fully prepared, and I need to improvise.

For example

I enjoyed the January full moon with my workshop group in Death Valley and the Alabama Hills; in February my Horsetail Fall workshop group photographed a full moon rising above Yosemite Valley; in March I was in Sedona with Don Smith to photograph the full moon as it rose above Cathedral Rock and Oak Creek; and last week my Yosemite Moonbow and Wildflowers workshop group photographed the April full moon above Bridalveil Fall and the Merced River Canyon, then headed off to catch a moonbow in the mist at the base of Lower Yosemite Fall. And chasing the moon isn’t all about the full moon—already this year I’ve photographed several thin crescents in the Sierra foothills, and next week I raft Grand Canyon, where my group will (fingers crossed) witness a waning crescent moon just after sunset, and later that night photograph the canyon illuminated by nothing but the Milky Way and thousands of stars only visible in a moonless sky.

All this planning around the moon does indeed get me to many beautiful locations at just the right time, but sometimes the moon catches me in situations where, without the necessary knowledge at hand, I’m forced to think on my feet (and smartphone). Most recently was the unplanned moonrise added to last week’s Yosemite workshop. When the National Park Service opened Glacier Point about a month earlier than expected, I quickly inserted a Glacier Point sunset into the workshop but didn’t have time for anything more than a cursory moonrise check.

Beautiful clouds and light made our Glacier Point sunset a success, but as we were about ready to return to the warmth of the cars, the moon’s imminent arrival crept into the back of my mind. What I knew was that this night, from Glacier point the moon would be rising far to the right of Half Dome (out of the primary view), and probably just slightly too late to photograph effectively (not enough light to capture both landscape and lunar detail). Nevertheless, before packing up my gear I pulled out my iPhone to be certain we weren’t making the classic photographer’s mistake of leaving too early.

This won’t be on the test

Without a strong cell signal, I had to resort to apps that function offline. I started with Focalware, my go-to app for the sun’s and moon’s altitude and azimuth from any location on Earth. Next, now armed with the moon’s azimuth, I opened MotionX-GPS (with the map pre-downloaded) to plot its location relative to the current landscape, determining that it would emerge from behind Mt. Clark.

The final (and most difficult) piece of the puzzle was determining when the moon would appear. This is tricky because published moonrise times always assume a flat horizon—great if you’re on a ship at sea, but not so much anywhere else, and especially not in the mountains.

Using the topo info in the MotionX app, I determined that Mt. Clark’s elevation was around 11,500 feet. Knowing the Glacier Point is at 7,200 feet, I subtracted 7,200 from 11,500 and got 4,300 feet, the vertical distance between my location and the point where the moon would appear. Because the MotionX app also gave me the horizontal (as the crow flies) distance between me and Mt. Clark (about 8.2 miles, or around 43,300 feet), I had everything I needed to plug into my HP-11C (scientific calculator) app and compute the altitude, in degrees, that the moon would need to achieve before cresting the peak (thank God I stayed awake in trigonometry). With that information, it was a simple matter of returning to Focalware to see what time the moon would ascend to that altitude (appear above Mt. Clark).

There are apps that will do all this for me (PhotoPills and The Photographer’s Ephemeris are the ones I recommend), but they require connectivity, and the foresight to do the work when my signal is strong enough to download the maps. (Plus, I just like doing it my way.)

I never tire of this stuff

So, after less than five minutes of figuring, I was confident enough to tell everyone the moon would appear from behind Mt. Clark at 7:57 p.m., plus or minus two minutes. That gave us a couple of minutes to prepare a composition, and sure enough, right around 7:55, the clouds behind Mt. Clark started to glow; at 7:58, there it was and we were in business. In this case the thin clouds on the horizon subdued the moon’s brilliance just enough that I could give the foreground enough light without turning the moon to a white disk.

As often as I do this (sometimes I plot the moon just for fun, even though I know I can’t be there to enjoy it), few things thrill me more than my eyes on the exact point on the horizon at the moment the moon first nudges into view.

Understanding vs. knowledge

I know my process sounds complicated, but it really isn’t—in fact, plotting the moon this way doesn’t require any special insight beyond what most of us learned in high school. But it does illustrate something I constantly stress: the advantage of understanding over knowledge. When we know something, we can respond to a finite set of circumstances; when we understand something, we can reason our way to knowledge beyond our training.

One more quick example: A couple of days ago, I was scouting a potential sunrise location in the Columbia River Gorge. Because I’m reluctant to trust compass apps that point an arrow (or whatever) in a general direction, I pulled out Focalware and saw that tomorrow’s sunrise azimuth would be 70 degrees. Focalware also told me that the sun’s current azimuth was 253 degrees. Since I know that a (solar) shadow always points exactly 180 degrees from the sun’s current azimuth, I knew that my shadow was pointing directly at the 73 degree azimuth (253 minus 180), more than close enough to figure out where the sun would appear (in this case, farther north than ideal).

Whether it’s lunar geometry, exposure settings, depth of field, or whatever, understanding (and visualizing) a system’s underlying principles is always superior to memorizing its facts. And amazingly, it’s almost always simpler than we imagine. Since the position of the sun, moon, and stars are important to me, I try to visualize the celestial choreography.

Likewise, the more you can understand what’s happening when you adjust your shutter speed, f-stop, and ISO, the better prepared you’ll be to reason your way through difficult exposure puzzles, such as, I really need a lot of depth of field to get this tree and that mountain sharp, but the breeze is really blowing the leaves?, or, The exposure is perfect for this 20-second pinpoint stars image, but how can I do a 30-minute star trail shot of the same scene without changing the exposure?.