Sunset on the Moon

Old sci-fi movies whose adventures take place on the moon have a standard look, their sets filled with soaring crags, elongated spikes, deep cracks and sheer-sided craters. Think of the 1964 film, “First Men in the Moon,” which had the added delights of nasty “Selenites,” big, intelligent, insect-like creatures.

Besides the disappointing lack of moon monsters, reality differs from Hollywood in another way: gentler formations. Up close, even some of the most dramatic terraced craters, like huge Copernicus, are less vertical than they look in films’ special effects. In a photo from an Apollo landing, an astronaut standing beside a moon mountain looks like he is next to a large rounded hill. The explanation involves lighting and the moon’s lack of an atmosphere.

Moon features that pop out dramatically for viewers are along the terminator, the line between sunlight and darkness on Luna’s surface. Wherever it happens to be, at the terminator, crater sides and mountains cast long shadows, just as a person does standing in late afternoon sunlight. Elongated shadows give a rugged definition to the moon’s formations, exaggerating their steepness. Meanwhile, sunlight glares on crater rims, which appear stark white against a black backdrop. Without an atmosphere to blur the view, the moon looks like a harsh mistress indeed.

[A view I took of the moon’s south pole region on Oct. 9, 2009. The sunlight casts long, dramatic shadows]

This exaggeration is the cause of the films’ false impression about moon topography.

The difference comes through in telescopic views of our only natural satellite that I took yesterday (Wednesday) morning. The location was in front of the San Rafael Reef in Wayne County. Dawn was lighting some of the miserable clouds that had plagued me most of the night. The moon was fairly close to the horizon, which meant that its photons had to swim through denser layers of air than if it had been high above. Nearly to the new stage, the moon displayed a narrow crescent where sunlight blazed.

The darker region was more interesting; that is, the majority of the moon where direct sunlight did not fall. This portion was lit by Earthshine, which is sunlight bouncing off Earth and hitting the moon. It was a faint, even glow that seemed eerie and calm. It diminished the effects of shadows. As opposed to side-lighting from the sun that would create long streaks and spikes at the terminator, our planet’s glow came from overhead to the moon. Reflecting from cloud tops, oceans and land masses, it was a more spread-out lighting, dim and soft. Craters and mountains that it illuminated were soaked in a mellow light, showing speckles and gentle rills.

I photographed the south polar region with a slice of the bright crescent showing. It was shortly before new moon, when the opposite side of the moon gets all the sunshine, so this was sunset on Luna. Where the late sunlight hit, rims and hills blazed intensely, overexposing those parts of the image, turning them into big white blobs. But most of the view was lighted only by Earthshine, rendering the moonscape flat, a peculiar view we seldom see but one that may be closer to the reality of the formations’ shapes.

[Sunset on the moon, a view I took the morning of June 9, 2010]

As I watched the pictures coming in, breezes rippled our atmosphere so that the ancient surface seemed to move, parts expanding and shrinking like the hide of a breathing elephant.

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