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SYFY WIRE Bad Astronomy

A Twice-Lit Moon Kisses the Horizon

By Phil Plait

Sometimes you see a photograph that’s just so wonderful you can’t wait to show it to other people.

That shot above is one of those photos.

It was taken by Petr Horálek, a European Southern Observatory Ambassador—the ambassadors are a group of excellent photographers who shoot pictures of the ESO observatories for public outreach.

The photo was taken on April 6, just minutes before sunrise. Smack dab in the center is Venus, cruel twin of the Earth, covered in clouds so reflective they make the planet the third brightest natural object in our skies.

Below it is the crescent Moon, less than a day before its new phase. The crescent is so thin it’s almost an afterthought. Amazingly, the rest of the Moon’s surface was unlit by the Sun. So why can we see it? Earthshine! Light from the Sun hits the Earth, reflects off of it, illuminating the Moon, which then reflects it back into space, and to Earth. Our planet is very bright in the lunar skies, 50 times brighter than a full Moon. That’s enough to softly bathe the surface of our satellite in light.

Note too the Moon looks a little squished. That’s an effect of our atmosphere, which curves along with the Earth’s surface. Near the horizon, the light from the bottom of the Moon goes through a thicker layer of air than the top part of the Moon. The air acts like a lens, bending that light, making the Moon look flat.

Horálek timed this photo perfectly, getting the shot just as the Moon cleared the distant mountains. Had he waited much longer the Sun would have lit things up too much anyway. This was a time exposure, too: You can see the faint stars of Pisces surrounding the Moon and Venus.

And let’s not ignore the foreground! The silhouetted dome houses the 1.2 meter VLT Auxiliary Telescope, part of the Very Large Telescope array. See the two people crouched nearby? That’s my friend Babak Tafreshi on the left and Yuri Beletsky on the right, wrapping things up after a long night of photography in the incredibly rich and dark skies of this remote location in the high desert of Chile. I’ve featured both their works on this blog many times; click their names to fill your eyes and brain with delight.

I dream of capturing a photograph like this some day. But I just dabble in this; Horálek, Babak, and Beletsky are professionals. I might feel a pang of jealousy seeing shots like this, but it evaporates rapidly as I take in the sheer beauty. I’m glad there are so many people out their willing to collect the few photons the Universe graces us with, and share them with the world.

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