yosemite moonbow

Calculations by Brian Hawkins


2020 Moonbow season


I hope everyone is looking forward to spring of 2020 for Yosemite moonbows. If you’re planning a trip to see this exciting phenomenon, plan to visit within a few days of a full moon during April, May, or June, when waterfalls are at their peak flow.

Full Moon Dates Spring 2020

April 5 - April 9

May 5 - May 9

June 3 - June 7

July 2 - July 6

As we get closer to spring, I’ll calculate the specific times/locations for when to see them and list them below. In the meantime, pray for lots of snowfall this winter so we’ll have raging waterfalls this spring!

Moonbow in Lower Yosemite Fall by Brian Hawkins120506-67838t.jpg

Lower falls predictions

Moonbows in the lower section of Yosemite Falls are most often seen and photographed from the footbridge closest to the base of the falls on the Lower Falls Trail (Google Maps Link).  The moonbow arc forms high and to the left of the base of the falls and slowly sinks down and to the right during the hours it is present. 

2019 Moonbow Dates/Times

2019 Moonbow season has ended. I will publish predictions for 2020 moonbows as we approach April 2020

Moonbow in Upper Yosemite Fall from Sentinel Bridge by Brian Hawkins.jpg

Upper falls predictions

Moonbows in the upper section of Yosemite Falls can be seen and photographed from the parking lot near Sentinel Bridge (Google Maps Link).   Please note that these times are for viewing the moonbow in Upper Falls from this location and are not valid for viewing from the Upper Falls Trail. In April and early May, the moonbow in the upper falls is positioned very low, but may be noticeable if there is plenty of spray over the middle cascades.  Full-moons in late May and June are the best opportunities to see this moonbow. If you venture away from the parking lot, please take care not to damage the surrounding meadows.

2019 Moonbow Dates/Times:

2019 Moonbow season has ended. I will publish predictions for 2020 moonbows as we approach April 2020

Moonbow in Yosemite Falls as seen from Glacier Point just before midnight April 28, 2018

Glacier Point predictions

Moonbows seen in the upper falls from Glacier Point are rare since the road to Glacier Point usually doesn't open until late spring and you have to look for them at precise times.  Since Glacier Point is farther from the falls, the moonbow appears wider and sweeps through the area of mist much faster.  Consequently, the opportunity to see it is only about 15 minutes each night.  The predicted times are for the optimal position within this short viewing window.

2019 Moonbow Dates/Times:

2019 Moonbow season has ended. I will publish predictions for 2020 moonbows as we approach April 2020


What are moonbows?

Moonbows, also known as "lunar rainbows," are rainbows which form at night due to the light of the moon.  When the moon is full and shining at the correct angle on the spray of a large waterfall, a moonbow can be seen arcing through the mist.  John Muir wrote about their occurrence in Yosemite in the 1800s but only recently has their popularity increased due to photography.  To learn more, check out this excellent video produced by Steve Bumgardner for the Yosemite Conservancy.


Conditions for moonbows

There are a few conditions necessary for moonbows to be observed at Yosemite Falls

  1. Moon must be within a few days of being full

  2. Clear skies between the moon and the waterfall

  3. Plenty of water in the falls (typically April-June)

  4. Sufficient darkness (at least one hour after sunset or one hour before sunrise)

  5. The moon must have risen high enough to shine on the waterfall spray

  6. Wind can greatly enhance the moonbow by carrying the water spray

  7. The moon must be at the proper angle relative to the observer (see the predictions listed above for when and where to be to make everything line up)

Viewing moonbows

To the human eye, moonbows typically look dull and colorless, appearing as a gray arc in the mist of the waterfall. This is because human color vision sensitivity is reduced in low light environments. The photograph below simulates what our eyes see when viewing a moonbow with our eyes for the first time. With sufficient time to adjust to the low light, the colors will become more apparent, but not as vivid as they appear to a camera.  To help your eyes adjust, turn off your flashlight and avoid looking at your smartphone screen.  Consider using a flashlight with a low-power red light if you still need a little light to move around safely.  The movement of the moon across the sky causes the moonbow to slowly change position over time and the moon rises approximately 50 minutes later each evening, so don't expect to see moonbows in the same position each visit.  

moonbow camera versus human eye comparison.jpg

Predicting moonbows

To learn more about how I calculate when moonbows can be observed at Yosemite Falls, click here.

Photography tips

Moonbows are much easier for a camera to see than the unaided human eye.  Most any camera with the ability to take long exposures can be used for moonbow photography, but smartphone cameras and fully automatic point-and-shoot cameras will not be able to photograph such dark scenes.

Recommended exposure settings:  15 seconds, at f/4, at ISO 1600 (this will probably look overexposed on your camera’s screen, but trust your histogram, not your eyes).

Shutter speed considerations: Though it may be tempting to use a longer exposure time in order to reduce ISO or gain depth of field, an exposure time longer than one minute will cause the colors of the moonbow to blur together as it slowly changes position.  Also, longer exposure times may not be practical if shooting from a location where mist is accumulating on the lens. 

The lower falls viewing area is often enveloped in the mist of the waterfall.  Bring a microfiber cloth or squeegee to dry your lens between shots or blow the water off using compressed air.  You might also consider using a hydrophilic filter, or coating an ordinary glass filter with Rain-X (you may want to avoid this for precious micro-coated filters, though).  Also, cover your camera with a towel or plastic bag to keep it dry.

Turn off the camera flash since it will ruin everyone's photo, including your own.

Etiquette and other tips

  1. Please keep the viewing areas dark to avoid ruining photographs and disrupting the enjoyment of the natural moonlight. Turn off your flashlight (or use a low-power red light instead) and shield your smartphone and camera screens. Turn off your camera's flash.

  2. Be aware of others around you, taking care not to block their view or bump their tripod.

  3. Wear a waterproof jacket at the lower falls, but avoid using umbrellas since they make it difficult for others to see or photograph.

  4. Consider viewing the upper falls moonbow first since its viewing times are generally about an hour before those for the lower falls.

  5. Avoid trampling the sensitive areas of Cook's Meadow when photographing the upper falls.

  6. As always, be safe around fast moving water and wet rock surfaces.

Brian Hawkins filming moonbows during the epic springtime conditions of 2017

Brian Hawkins filming moonbows during the epic springtime conditions of 2017

connect with me

Photographing moonbows combines my passion for photography, science, and the outdoors.  As a former mechanical engineer, I started making my own 3D simulations of Yosemite Valley in 2011 to discover new places to photograph moonbows and the best time to be there.  I hope this information is helpful to you as well.  

Say hello if you see me in Yosemite this spring, or reach out on social media to stay connected.