The Moonbow Challenge

Last updated on September 16, 2023

The Moonbow Challenge: A Rare and Magical Sight

Moonbows, also known as lunar rainbows, are a captivating atmospheric phenomenon that enchants those lucky enough to witness them. These ethereal displays occur when the moon's light refracts and reflects off water droplets in the air, creating a shimmering arc of colors against the night sky. While all moonbows hold a certain allure, one particular moonbow recently caught the attention of moonbow collector Martin McKenna in Northern Ireland on November 20th.

What made this moonbow particularly extraordinary was the phase of the moon at the time of its appearance. Typically, moonbows require a bright moon, preferably close to full. However, this particular moonbow emerged when the moon was past its 3rd quarter and only 7 days and 14 hours away from the next new moon. McKenna was astounded by its faintness, explaining that it lacked color to the naked eye and was produced by a weak last 1/4 Moon. The mere existence of a moonbow under these circumstances was unexpected and added to its uniqueness.

Moonbows are rare phenomena due to specific conditions that must align perfectly for their occurrence. Firstly, a bright moon is necessary, with a preference for it being as close to full as possible. Additionally, the moon must be positioned relatively low in the sky, combined with a dark backdrop of the night sky. Lastly, a rain shower opposite to the moon's position is required to create the water droplets necessary for the refraction and reflection of light.

The rarity of McKenna's moonbow lies in its distance from a full moon. It is quite likely that this particular instance set a record for being observed so far from a full moon. To explore further possibilities for capturing a bow even further from a full moon, one can utilize a planetarium program to identify potential locations and times when rainbows formed by rain might be visible. If you're up for the challenge, you can submit your entries to OpticsPOD and share your own moonbow encounters.

While we await new moonbow discoveries, let's take a moment to appreciate some of Martin McKenna's previous encounters with these mesmerizing celestial spectacles. Each photograph showcases the delicate beauty and otherworldly nature of moonbows, reminding us of the enchantment that awaits those who venture out under the right conditions.

In conclusion, the moonbow challenge presented by Martin McKenna's extraordinary find offers a glimpse into the magical world of atmospheric optics. The rarity of this particular moonbow, observed so far from a full moon, highlights the exceptional nature of these phenomena. As we continue to explore and appreciate the wonders of the night sky, let us remain open to the possibility of encountering the elusive moonbow and allowing its ethereal charm to captivate our senses.

All moonbows are special - what is extra special about this one by moonbow collector Martin McKenna (more moonbows) imaged in Northern Ireland on November 20th?

The moon's phase. It was past 3rd quarter and only 7days 14h from the next new moon. "I just caught the faintest Moonbow I have ever seen.. ..It had no colour with the naked eye but was produced by a very weak last 1/4 Moon. I was surprised to see one at all with that moon phase."

Moonbows are so rare because they need a bright moon, the closer to full the better. They also need a combination of the moon fairly low, a dark sky and, of course, a rain shower opposite.

Martin's bow so far from a full moon is likely a record.

Some time spent with a planetarium program will show where and when a bow further from a full moon and made by rain might be captured. Send challenge entries to OpticsPOD!

In the meantime, here are a few of Martin's earlier bows.

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Reference Atmospheric Optics

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