Telescope Moonrise

A tricky shot, taking very precise timing and navigation. I can not claim credit, Sean Goebel did the planning. I just supplied scouting information and came along for the ride.

Mauna Kea Telescope Moonrise
The Moon rising directly behind the telescopes on the summit as seen from near Waikoloa
Sean has been after this photo opportunity for some time. For months he has messaged me to check on the weather over the Waikoloa area each time a full Moon is available. As he has to drive across island to reach the correct locations, a look ahead at the weather can save a great deal of wasted time.

Given that this only involved a fifteen minute drive from the house for me… Why not? Give it a try. Besides, I already had a suitable telescope loaded in the vehicle.

I have a friend in Tucson, Dean Ketelsen, who has worked out several spots from where the setting Sun can silhouette the telescopes of Kitt Peak. His favorite spot is a particular viewpoint on the Mt. Lemmon Highway. On the correct dates you can shoot the telescope silhouettes from 60 miles away.

Our target was only half that, about 32.5 miles from where we were set up. Still it is a much more difficult proposition.

The Moon is a much tougher target than the Sun, its motions more complex and not repeating neatly every year. Unlike Dean’s Kitt Peak expeditions, you cannot scout a location in spring, and try again in the fall, or the next year.

With the Moon you must also get the phase right, preferably quite close to full Moon as it rises and sets with the Sun.

The difference is applications like PhotoPills, or websites like The Photographer’s Ephemeris you can plan these events with a fair amount of precision.

And the precision was quite good. Sean set up the shot perfectly, the Moon rising directly behind the telescopes on the summit. It was actually quite impressive to watch the full Moon rise between the domes.

Mauna Kea Telescope Moonrise
The Moon rising directly behind the telescopes on the summit as seen from near Waikoloa
On this night the correct spot was right beside the very busy Queen Kaʻahumanu highway. While we pulled off as far as we could into the lava, it was still just twenty feet to constant 60mph traffic behind us. Not exactly a peaceful place to observe from.

We almost did not get the shot. Clouds appeared at sunset and blocked the scene. Arriving at the correct site I could not see the summit, I feared Sean’s run across island was in vain, at least I only had a few minutes drive invested. With just 20 minutes to spare the clouds started to break and we hurriedly set up telescopes and cameras. There was still a trace of clouds over the summit when the Moon rose, but they did not present any real issues.

For a telescope I used my recently assembled eclipse rig, another opportunity to give it some testing before I pack it in a suitcase for the trip to Oregon.

Shooting through thirty miles of air there is a price to be paid, a fair amount of atmospheric distortion is visible in the images. I looks like I got the focus pretty close, always my main worry on a shot like this.

Thanks to Sean I got the frame, I have yet to hear how his material came out. Need to do this again sometime when it is a day before full, and the summit is more visible.

Author: Andrew

An electrical engineer, amateur astronomer, and diver, living and working on the island of Hawaiʻi.

One thought on “Telescope Moonrise”

  1. I’ve never tried to chase the moon silhouette behind Kitt Peak – too many things going against it, not least of which is hourly movement, and variations of extinction near the horizon. At least with the sun near winter solstice, there is no motion to speak of day to day, and lots of light.

    Though I will have to admit when Tom Polakis calculated where we would need for Venus to set behind 4-meter dome, he got it to within a couple feet – using Google Earth, I believe…

    http://theketelsens.blogspot.com/2017/03/the-evening-star-moves-on.html

    -Dean

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