Moon Dogs, Paraselenae, Tucson, Arizona

Moon Dogs, Paraselenae, Tucson, Arizona: A Spectacular Atmospheric Phenomenon

When it comes to atmospheric optics, one of the most captivating phenomena to witness is the occurrence of moon dogs, also known as paraselenae. These mesmerizing displays of light can be observed in various locations around the world, including the beautiful city of Tucson, Arizona. While moon dogs are often associated with diamond dust, a type of ice crystal, it is worth noting that they can also form in high cirrus clouds, making them visible even in desert regions like Tucson.

Understanding Moon Dogs and Their Formation

Moon dogs are a type of halo that appears as two bright spots on either side of the Moon. They are caused by the refraction and reflection of light through ice crystals present in the atmosphere. These ice crystals act as prisms, bending and dispersing the light, creating a stunning visual effect. Moon dogs typically occur when there is a thin veil of cirrus clouds, allowing the moonlight to pass through and interact with the ice crystals.

The Role of Diamond Dust in Moon Dog Formation

While the presence of diamond dust is commonly associated with moon dogs, it is not always necessary for their formation. Diamond dust refers to tiny ice crystals that resemble glittering diamonds when illuminated by light. These crystals can form in cold regions with temperatures below freezing, such as the Arctic or Antarctic. However, in Tucson's desert climate, where diamond dust is rare, moon dogs can still occur through the interaction of moonlight with ice crystals in high cirrus clouds.

Witnessing Moon Dogs in Tucson, Arizona

Tucson, Arizona is renowned for its clear skies and favorable conditions for stargazing and observing atmospheric phenomena. The city's location in the Sonoran Desert provides a unique opportunity to witness moon dogs without the need for diamond dust. When the conditions are right, such as during the presence of high cirrus clouds, Tucson residents and visitors may be treated to the awe-inspiring sight of moon dogs illuminating the night sky.

The Visual Splendor of Moon Dogs

When moon dogs grace the sky above Tucson, they add an ethereal touch to the already breathtaking lunar scenery. The two bright spots on either side of the Moon create a symmetrical and mesmerizing display. Additionally, moon dogs are often accompanied by other atmospheric phenomena, such as the parhelic circle. This circular halo appears as a faint arc extending horizontally from the Moon, further enhancing the visual spectacle.

Capturing Moon Dogs on Camera

Photographing moon dogs can be a rewarding experience for both amateur and professional photographers. To capture the beauty of these atmospheric phenomena, it is essential to have the right equipment and settings. Using a camera with manual controls, such as a DSLR, allows for greater flexibility in adjusting exposure settings. A wide-angle lens is also recommended to capture the entire scene. Setting the ISO to a low value, around 200, and using a long exposure time, such as 30 seconds, can help capture the intricate details of moon dogs and their accompanying halos.

Other Atmospheric Optics Phenomena in Tucson

While moon dogs are undoubtedly captivating, Tucson offers a myriad of other atmospheric optics phenomena for enthusiasts to explore. Some notable examples include:

  • Halos: These luminous rings around the Sun or Moon are caused by the refraction of light through ice crystals or water droplets in the atmosphere. Tucson's clear skies make it an ideal location to observe various types of halos, such as 22-degree halos and circumzenithal arcs.
  • Sun Pillars: These vertical shafts of light appear above or below the Sun and are caused by the reflection of sunlight off ice crystals in the atmosphere. Sun pillars can create a dramatic and mystical effect in Tucson's sky during sunrise or sunset.
  • Rainbows: Tucson's occasional rain showers provide opportunities to witness vibrant rainbows. These colorful arcs form when sunlight is refracted, reflected, and dispersed by raindrops in the atmosphere.


Moon dogs, or paraselenae, are a captivating atmospheric optics phenomenon that can be observed in Tucson, Arizona. While diamond dust is often associated with their formation, moon dogs can also occur through the interaction of moonlight with ice crystals in high cirrus clouds. Tucson's unique desert climate provides an ideal backdrop for witnessing these awe-inspiring displays of light. Alongside moon dogs, the city offers a wealth of other atmospheric optics phenomena, making it a haven for enthusiasts and photographers alike. So, next time you find yourself in Tucson, keep an eye on the night sky for the enchanting sight of moon dogs illuminating the darkness.

Imaged by Steve West (Steve's Atmospheric Phenomena) on Feb 23rd 2008 in Tucson, Arizona. ┬ęSteve West , shown with permission

"There was just the weak halo until this wedge-shaped clearing pushed in above the moon. Then the two dogs and a bit of the parhelic circle lit up for about 10 minutes. Shot at ISO 200 for 30sec with a Konica Minolta 7D and Sony 11-18 lens. No diamond dust here in the desert!"

A bright moon makes halos and luckily we do not always need diamond dust. Halos formed by ice crystals in high cirrus clouds can be seen anywhere on Earth summer and winter.

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