Home > Concepts, Ephemeris Program, Phases, The Moon > 08/16/2018 -Ephemeris – The Moon’s phase, a closer look

08/16/2018 -Ephemeris – The Moon’s phase, a closer look

August 16, 2018

Ephemeris for Thursday, August 16th. The Sun rises at 6:46. It’ll be up for 14 hours exactly, setting at 8:46. The Moon, 2 days before first quarter, will set at 11:59 this evening.

With the Moon at a fat crescent tonight, it’s a good time to turn binoculars or a small telescope toward it. The demarcation between the bright part and the dark part is called the terminator. In the case before full moon, it is the sunrise line. After that the sunset line. The Moon’s entire day lasts about 29 ½ earthly days. I am sometimes asked “What’s blocking the light from the unlit side of the Moon?” It’s the Moon itself. It’s the night side of the Moon, just as when we are in night. The Earth itself is blocking the Sun’s light from us. The Moon, like the Earth and all the other planets are spheres lit on one side by the Sun. It’s near the terminator of the Moon where the most detail is revealed by the long shadows cast by the Moon’s features.

The times given are for the Traverse City/Interlochen area of Michigan. They may be different for your location.


Crescent Moon tonight

The crescent moon as it should appear tonight. Created using Stellarium.  Stellarium always shows details on the night side of the Moon.  The crescent phase of the Moon is now too fat to really see earthshine on it’s night side.

Moon ball

Demonstration of the Moon’s crescent phase with the Styrofoam moon ball we use for Project Astro held up to a light off frame to the right.  The night side of the ball is illuminated a bit by the translucency of the ball, and the reflection off my hand.  Note the roughness of the ball is visible only at the terminator.

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