A lunar rainbow is a rare and wondrous sight. Like any rainbow, it requires droplets of water in the air to diffract the light into colors. The light source has to be at the right angle, behind and above the observer, who is looking forward to the water droplets. What's unusual about a lunar rainbow of course is that it occurs at night. A full or nearly full moon is needed to get enough light to create a rainbow. Even with a full moon, our eyes can only see the shape of the rainbow, not the color. Color is seen by the cones in the eye, which require more light to activate than the rods in the eye, which  see in black and white. 

The arc of a rainbow is actually part of a 42 degree circle of diffraction. This means that the angle of light is critical for forming a rainbow.  A waterfall is a good place to see a rainbow because a waterfall is tall enough to allow the light source to achieve that right angle relative to the observer. For instance, as the moon rises, the arc of the rainbow moves down towards the base of the falls. If the observer is able to get higher, the rainbow appears to move higher up the waterfall. Upper and Lower Yosemite Falls attract a number of photographers because they are South facing and tall, increasing the likelihood of the photographer getting to the right angle to see a rainbow. The angle, sufficient water and a bright enough moon occur every Spring during the full moons of April, May and June. 

I had gone to Yosemite in April of 2014 to photograph a lunar rainbow on Lower Yosemite Falls. I checked out the location during the afternoon, went for dinner and came back after dark to find the bridge near the base of the falls jammed with photographers. I was barely able to get a spot.

Before setting up my camera, I looked towards the falls and could just barely see a silvery arc near the base of the falls! A lunar rainbow! What a magical sight. I felt privileged to see it. I quickly began the process of setting my camera up to see it.

The hardest thing about night photography is focus, so the first thing I did was turn towards the moon and manually set the focus ring to create the sharpest image in the viewfinder. Next, I took a guess about exposure, attached the camera to the tripod, removed the lens cap again and began trying different combinations of ISO and time.

To complicate matters, mist from the falls was blowing into our faces, drenching us and our cameras. I learned that night that I needed to cover my camera to protect it from water and that I needed a chamois cloth, not just a paper lens cleaner to keep my lens dry.

I did come away with a pretty good image from that night but was not satisfied because the trees were blurry from wind movement and even the rocks were soft looking because of the mist on my lens. I was using a 35 mm prime and I wasn't satisfied with the field of view either. I wanted to see more stars to convey the idea of a rainbow at night to the viewer.

Lower Yosemite Falls 2014

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I never printed this because it looked like an underexposed, blurry rainbow. It really didn't tell the story or convey the magic of a lunar rainbow.

So I went back this year in June of 2016 to try again. It had been a wet Winter, so the falls were going to be good. Having used a plastic bag on my camera earlier this year in Upper Antelope Canyon (because the guides are throwing sand in the air) and on my river trip down the Grand Canyon (to protect against water spray in the rapids), I was adept at cutting a hole in a plastic bag and attaching it to the barrel of my lens with a rubber band. I also bought a chamois.

Camera with plastic bag, rubber band & chamois

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The technique is not difficult. Just use the lens cap to trace a hole in a plastic bag using a sharp knife. Remove the lens cap and complete cutting the hole. Stretch the hole over the lens and attach using a rubber band. The hole doesn't have to be perfect as the rubber band will seal the fit. Use a bag long enough to pull completely over the camera. I cut a slit at the bottom to allow the bag to easily pass the tripod.

This year, I checked the moon bow predictions on the website of Don Olson of the University of Texas http://donolson.wp.txstate.edu/moonbows-lower-yosemite-fall. Every year, he gives the best times to see a moon bow from both Upper and Lower Yosemite Falls. 

Booking a place to stay was a challenge. All the campsites were long gone and there was only one night available at Yosemite Lodge. We booked that and also booked two days before and two days after the Lodge night at the Indian Flats Campground and RV Park in the Merced River Canyon outside the park. We drove up from Los Angeles on Friday and spent the night in a comfortable tent cabin at Indian Flats. The cabin had a king bed, two small tables, two chairs, a laminate floor and by the time we left, a small refrigerator. We would stay there again.

The next morning, we drove towards the park and were surprised to see a mile long line of cars waiting to get into the park. I thought to myself, "Well, that's why I never come here in the Summer."

After we got through the gate, we drove along the Merced until we reached the Valley floor. Again to our surprise, we found ourselves in bumper to bumper traffic as we approached the Pohono Bridge. One lane was blocked off with a large flashing sign that said, "For emergency vehicles only." We crept forward, covering less than a quarter mile in 15 minutes. As soon as we could, we turned right, away from the valley towards Glacier Point.

We moved quickly again but then were stopped by another line of cars just before the ski area. A ranger was diverting all the cars to the ski area to park and wait for a shuttle bus to Glacier Point. We were puzzled by this and dismayed by the line of at least 600 people waiting for a bus so we asked the ranger at the head of the line if we could just go up to McGurk Meadow. He said, "Sure" and motioned us on. 

By now, it was getting to be lunch time, so we stopped before McGurk at a beautiful meadow with a pull out beside the road and a vault toilet. I took photos there and Eileen got out our lunches. 

Meadow along Glacier Point road.

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Outhouse in Paradise

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Another couple pulled over while we were eating  and we chatted with them. I said how weird it was that the park service had blocked access to Glacier Point and were offering a shuttle service to the top. The man said, "It's probably because of Obama."

"What? What about Obama?" 

"He and his family are at the park. He was just giving a speech in Cook's Meadow celebrating the Centennial of the formation of the National Parks Service. Rumor has it that he wanted to take his family up to Glacier Point in the early afternoon."

No sooner than he spoke, a CHP motorcycle officer pulled over to us and said, "You have to stay right here."

I asked, "Why?"

He said, "I can't say. You just have to stay here for a few minutes."


A few minutes later the roar of about 25 CHP motorcycles came up the road. They sped by followed by  three black SUV's with dark windows and lots of antennae on top close behind. Then came an armored looking car with what looked like a SWAT team followed by the press bus. As soon as they passed, the CHP officer sped off to join them.

"Well that explains the that", I thought to myself.

SWAT car

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After lunch, we hiked McGurk Meadow. There was an old cabin beside the trail. I mostly took close ups of flowers, of which there was a large variety. The meadow itself wasn't as pretty as the spot by the road where we had lunch. We named that one "Shooting Star Meadow".

McGurk cabin

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Later in the afternoon, we hiked to the top of Sentinel Dome. It is only about a mile from the parking area off Glacier Point road. Sentinel Point is just opposite and above Yosemite Falls.

View from part way up Sentinel Dome

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Later, as we drove on towards Glacier Point, we saw some lovely wildflowers growing right along the side of the road. Of course, I had to take a few photos. Further down the road, we passed some snow flowers. I stopped for those as well.

Wildflowers by Glacier Point road

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Snow flowers

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We pulled out at Washburn Point. This is the best viewpoint for looking down on Vernal and Nevada Falls.

Vernal and Nevada Falls from Washburn Point

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After checking out Glacier Point, we headed back down the mountain to the Valley floor for dinner and our date with the moon bow. Degnan's Loft has pretty good food, not great but fairly quick and wholesome.

We finished dinner by around 8:30 PM, found a parking spot near the trail to Lower Yosemite Falls and began our walk up. It was getting dark slowly because it was June 21st, the longest day of the year. The full moon was rising behind us as we walked up the trail. Apparently, the last time there was a full moon on the Summer Solstice was over 70 years ago. It is a rare enough occurrence to have it's own name, "Strawberry Moon".

As we approached the bridge, I checked my focus and set my camera so that I wouldn't have to do that in the blowing mist.

Since we were arriving late, I was expecting difficulty getting a spot to set up. I brought a tall tripod in the hope of shooting over a shorter person's shoulder. To my pleasure and surprise, when we came in sight of the bridge at the base of the falls, there were no photographers on the bridge, just a few over to the left. Also, there was hardly any spray blowing in my face either. I paced back and forth on the bridge looking for the spot where the rainbow's silvery arc was strongest, quickly set up and took a shot.

Photographers shooting the moon bow from left of the bridge

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My focus was good and my initial guess of four seconds at ISO 1600 proved to be good also. I was using my Canon 16-35 mm zoom at 16 mm. This gave me the sky that I was missing from my earlier attempt in 2014. I took another shot with more of the river and to the right of the photographers.

Lower Yosemite Falls moon bow from bridge

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Wow! I had been there less than five minutes and I already had a printable photo. I next tried over to the left with the other photographers. I knew there was a log there that would make a pretty good foreground.

Lower Yosemite Falls moon bow with log

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The log gave me a chance to make a horizontal image instead of the verticals I had just taken. It also allowed me to see that my focus was good from near to far as both the log and the stars were all sharp.

A few minutes later, a drenched and somewhat wild looking man stumbled out of the bushes and showed me his viewfinder. "See what I just got?" he said. 

I looked and said, "That's a beautiful shot. How did you get it?"

"I climbed up along the rock wall next to the waterfall as far as I could go. You should try it"

Thinking my wife would kill me if a fall into the river didn't, I said, "I think I should check it out in the daytime first."

He showed a couple more people his shot and soon there was a small group that wanted to go. The man said, "OK, follow me. But come at your own risk. It's wet and slippery up there."

I fell in quickly right behind him and we ascended through the trees and boulders beside the river. The air soon became heavy with a wet mist blowing in my face. Thirty feet further and I was dripping all over. I was glad I had my camera wrapped in a plastic bag. The leader of our little group stopped and pointed a little way further on. I climbed up and found the prime spot to frame my shot and quickly set up my tripod. I aimed the camera as best I could without taking the lens cap off to check my viewfinder. It was practically raining on me at that point. I pulled off the lens cap and pressed the shutter release, glad that I only needed four seconds in this mist. When the shutter clicked off, I used the chamois to dry the lens and quickly replaced the lens cap. What I saw in the rear lcd looked great! I adjusted the camera angle slightly and took one more shot, knowing I had a good one. Of the other people who followed, one had an iPhone. The others just wanted to see it with their eyes. The guy who led us there didn't have a full frame camera so I knew I got the best shot of everyone there, just based on equipment. The rest of the group got lost trying to come down, so I ended up finding a way and leading them back to the bridge.

The winner! - Lower Yosemite Falls moon bow

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The next day, we were tired. After relaxing in the morning and having lunch at Degnan's Deli, we went for the short hike to Mirror Lake and took some shots.

Mirror Lake looking East

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Half Dome in Mirror Lake

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That night, I went out into Cook's Meadow to try for a moon bow on Upper Yosemite Falls. The problem that night was clouds and a lack of mist to create a rainbow. I did get an interesting view of the falls with cloud shadows.

Cloud shadows on Yosemite Falls at night

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Eventually, the moon came out from behind the clouds and we began to see a hint of rainbow at the base of the falls where all the mist blows out into the little valley between Upper and Lower falls.

Rainbow on Upper Yosemite Falls base at 70 mm

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Though it is a lovely image, what I had in mind was a full rainbow arcing across the falls. I realize now that the blowing mist needed to make this a reality is a very rare phenomenon. I think I will try again next April or May.......or both.

The following day, we decided to hike part of the Panorama Trail, down from Glacier Point to the bridge just past Ilillouette Falls. We took our time on the way down, photographing wildflowers and enjoying the scent of Ceanothus, the California wild lilacs that grew along the trail.

Ceanothus along Panorama trail

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Of course, I kept watching for rainbows on Vernal and Nevada Falls below.

Vernal Falls rainbow from Panorama Trail (200 mm zoom)

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Ilillouette Falls from trail - Always looking for rainbows.

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River towards Ilillouette bridge - a great place to stop and rest

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After our hike down to Ilillouette bridge, we hiked back up to Glacier Point for sunset. A beautiful sight in and of itself. But just after that, the real show began. The full moon rose over the Clark Range in the Sierras and beautifully illuminated their snowy slopes and the backside of Half Dome. What a lovely sight!

Moonrise from Glacier Point

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For everyone who has never been to Yosemite, especially those who live in California, I suggest you go. There is something there for everyone. Hope you enjoyed this article.



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