Maine Miraged Moon

Last updated on September 16, 2023

Maine Miraged Moon: A Phenomenon of Atmospheric Optics

Have you ever witnessed the mesmerizing sight of a miraged moonrise? Picture this: a full moon slowly emerges from the horizon, its once brilliant white hue transformed into a reddish glow. As it ascends, something peculiar happens - the moon distorts and separates into two, with the lower moon seemingly sliding back into the ocean. This captivating display is known as a "Maine Miraged Moon," a rare atmospheric phenomenon that typically occurs when the sun is setting. However, on February 9, 2009, John Stetson captured an extraordinary image of a miraged moonrise at Casco Bay, Cape Elizabeth, Maine.

Unraveling the Mystery: The Etruscan Vase Mirage

The Maine Miraged Moon is an example of what is commonly referred to as an "Etruscan Vase" or "Omega" mirage. These mirages are more frequently observed during sunset rather than moonrise. In this particular case, warm air at the surface of the ocean interacted with cooler air above, creating a rapid change in temperature gradient with height. The water temperature at the ocean surface measured a relatively warm 39°F (3.9°C), while the air above it was a chilly 18°F (-7.8°C).

The Role of Refraction in Mirage Formation

The phenomenon of miraging is primarily caused by the bending of light rays as they pass through layers of air with varying densities. Refraction, as this bending is known, tends to deflect rays towards denser (colder) layers. In the case of the Maine Miraged Moon, the rays from the moon were refracted upwards as they passed between the cool and warm layers of air.

The Dual Image Effect

When observing the miraged moon from a vantage point above the warmer layer of air, two distinct lunar images become visible. The first image is erect, meaning it appears upright and relatively unaffected by the mirage. This image is formed by rays that pass relatively undeflected above the warm layer. The second image, however, is lower and inverted, appearing as a mirrored reflection of the moon's lower portion. These rays are reflected upwards by the warm layer, creating the illusion of a second moon. Both images are equally "real" and contribute to the ethereal beauty of the mirage. This effect can be likened to the mirages often witnessed above hot road surfaces.

The Enigmatic Green Flash

Interestingly, the Maine Miraged Moon also shares similarities with another fascinating atmospheric phenomenon known as the "inferior mirage." This type of mirage is often associated with the legendary green flash observed during sunrise or sunset. In the case of the miraged moonrise, the region where rays pass through the strong temperature gradient at the warm-cold air boundary becomes vertically magnified. This magnification accentuates the typically invisible green rim at the upper limb of the moon, transforming it into a brilliant green flash. The flash is more easily seen during sunset, with precise timing and location being crucial to witness this captivating event.

Height Above Sea Surface: A Key Factor

To observe the Maine Miraged Moon and potentially witness the green flash, one must be positioned above the warm air layer. However, climbing too high above the sea surface can diminish the effects of the mirage. Therefore, finding the optimal height is essential for experiencing this awe-inspiring phenomenon in all its glory.

In conclusion, the Maine Miraged Moon is a captivating display of atmospheric optics that occurs when warm air at the ocean surface interacts with cooler air above. Through the process of refraction, rays from the moon are bent as they pass through layers of air with different densities, creating two distinct lunar images. This mirage is reminiscent of the mirages witnessed above hot road surfaces and shares similarities with the enigmatic green flash observed during sunrise or sunset. To witness the Maine Miraged Moon and potentially catch a glimpse of the green flash, one must find the perfect vantage point above the warm air layer while avoiding heights that diminish the effects.

Maine Miraged Moonrise Imaged by John Stetson at Casco Bay, Cape Elizabeth, Maine on February 9, 2009. ©John Stetson, shown with permission.

A full moon, reddened as the atmosphere preferentially scatters away blue light, rises slowly over the ocean. The first recognisable feature is Mare Crisium but as the moon climbs it distorts, separates into two and the lower moon slides back into the ocean. A rare classical 'Etruscan Vase' or 'Omega' mirage of the moon - more usually seen happening to the setting sun.

The mirage was produced by warm air at the ocean surface with cooler air above and the resulting air temperature gradient changing rapidly with height. Here the water was a relatively warm 39 F while the air well above it a cold 18 F. Rays from the moon were refracted back upwards as they passed between the cool and warm layers. Refraction always tends to deflect rays towards the denser (colder) layer. If you are above the warmer layer you see two lunar images or parts of them (1) an erect image from rays that pass relatively undeflected above the warm layer and (2) a lower inverted image from rays mirrored upwards by the warm layer. Each moon image is as 'real' as the other. The effect is not dissimilar to the mirage seen above a hot road surface.

This is the stuff of the Jules Verne 'inferior mirage' type green flash. The image region from rays passing through the strong temperature gradient at the warm-cold air boundary is vertically magnified accentuating the normally invisible green rim at the moon's or sun's upper limb into a brilliant green flash. The flash is visible at sunrise or moonrise but is more easily seen during the setting with the benefit of knowing exactly when and where to catch it. The mirage and possible flash depend on your height above the sea surface. You must be above the warm air layer but climb too high and the effects diminish.

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