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Moon and Regulus

February 4, 2015

As the Sun set on several robotic lunar landers in the 1960s, they photographed a bright glow above the horizon. Since the Moon has almost no atmosphere, the sky should go dark as soon as the Sun drops from view, so the glow couldn’t be like twilight here on Earth. Instead, scientists thought it might be something more intriguing: sunlight shining on electrically charged grains of dust that were levitating above the lunar surface.

That could be a problem for lunar colonies. The grains of lunar dust are small but jagged. If they can levitate above the surface, they could more easily get into sensitive equipment, creating short circuits or other problems.

But a more recent mission has cast some doubt on the idea of levitating dust. Known as LADEE, the craft was designed to study the Moon’s extremely thin atmosphere and any dust in the lunar sky.

And in fact, it did see an extremely thin cloud of dust around much of the Moon. The dust is churned up when small space rocks hit the lunar surface.

But LADEE found no twilight glow like that seen by the earlier missions, and no evidence that dust could have created the glow. That means that scientists may have to come up with another explanation for the mysterious lunar twilight.

And the Moon is just past full tonight, so it shines brightly. Regulus, the brightest star of Leo, is close to the left of the Moon as they climb into view, with the brilliant planet Jupiter well above them.


Script by Damond Benningfield, Copyright 2014

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