Earth is getting fainter. For proof, just look at the Moon – something that scientists have been doing for decades.

They’ve been looking at earthshine – sunlight reflected off of Earth. We see it lighting up the nighttime portion of the Moon – the part that’s not brightly lit by the Sun. It gives that part of the Moon a ghostly appearance.

Right now, most of the lunar hemisphere that faces our way is in earthshine. The Moon is a thin crescent in the early morning sky. It’s getting thinner by the day as it wanes toward “new.” From the Moon, though, Earth is getting fatter. It’ll be “full” in just a couple of days.

How bright Earth looks varies a good bit, depending on the exact distance, the amount of ice and cloud cover, and other factors. Clouds and ice are bright; land and oceans are dark. So as Earth turns on its axis, and different features rotate into view, earthshine goes up and down like a dining room light on a rheostat.

Earthshine varies over longer periods as well, as a result of Earth’s changing climate. If cloud and ice coverage goes down, so does Earth’s overall brightness. And several studies have reported that that’s just what’s happening. Earthshine isn’t as bright as it was decades ago. The difference is small but clear – providing slightly darker nights on the Moon.

Look for the Moon low in the sky before dawn tomorrow. The bright star Antares, the heart of the scorpion, is close by.

Script by Damond Benningfield