Look at the Moon and Feel Young Again

Watch for the return of the youthful crescent tonight. The moon will be just 1.2 days (about 29 hours) old. You'll need a wide open view to the southwest to see it best. Stellarium

Even if you're already young, I still encourage you to check out the moon tonight (Feb. 12). For the rest of us, seeing the childlike moon may recall the vigor and innocence of youth. Every month at dusk the crescent returns, reminding us that each lunation is a fresh opportunity to start again. Begin a project we've put off. Throw out useless documents. Cook something exotic.

This is a 1.5-day-old evening crescent from September 2020. Bob King

Look for the dainty crescent about a half-hour after sunset. Click here for your sunset time. You'll find the moon low in the west-southwest about 7° high, not quite a fist held at arm's length against the sky. For the Americas, only 1.5 to 1.8 percent of the moon will be illuminated by the sun, depending on your location. Eastern hemisphere observers will see a thinner, younger moon yet. The rest of the disk will glow faintly by sunlight reflected from the Earth called earthshine. 

Why do we see a crescent moon? Because it's nearly lined up with the sun! As the moon moves to the left in its orbit, that angle increases and more of it becomes exposed to sunlight. This is what causes the lunar phases. Sunlight reflected from the Earth off the moon and back to us dimly illuminates the non-sunlit part of the moon. Bob King

We see a crescent because from our perspective only the extreme edge of the moon is illuminated by the sun. As the moon continues along its orbit, the angle between it and the sun widens, exposing more of it to view. On Friday  (Feb. 12) the angle is a narrow 14°, but by the time the moon reaches first quarter phase, when it's half lit by sunlight, the angle increases to 90°. At full phase, the moon stands behind the Earth 180° opposite the sun and rises fully illuminated around sunset. 

The moon is always running circles around us. How long can we keep up? Eat your vegetables, and the crescents will keep on coming.

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