The Half Moon and the Lazy Earth

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Monday is the half Moon.  Officially, the last quarter.  It may be the coolest lunar phase and I’ll prove it.

Monday morning the 27th of June, any time at all, look around the day sky.  There it is, a perfect half Moon lit up on its left side.  The earlier you look the higher it will be.  It pops out because it happens to occupy the darkest part of the blue sky.

This is the only Moon that hovers directly in front of us as we zoom around the Sun. It serves as a kind of reconnaissance scout.  When you see it Monday morning you will be right there, where the Moon is located, 3 1/2 hours later.

This naturally brings up our planet’s motion.  We circle the Sun at a devilishly fast 66,600 miles an hour.  But that’s just our average. What’s strange is that we speed up and slow down.  Johann Kepler told us in the 17th century that planets move fastest when they’re nearest the Sun as they’re whipped around by the stronger gravity.

Earth was closest to the Sun on January 2, even if it didn’t feel like it. That was our fastest speed, some 67,000 mph.  And our slowest?  It happens at our planet’s aphelion or annual far point.  This year it’s on the 4th of July.  We’re essentially there now. Thus, right now we’re only traveling 65,500 mph. 

So, yes, we’ll be heading toward the Moon Monday morning.  But we’ll be taking our sweet time.

For serious sky-gazers: Monday morning’s half Moon has something to offer you, too. As it crosses our sky it also crosses the celestial equator, meaning it hovers right over Earth’s equator. Its declination reaches zero. And, amazingly, it ALSO sits at the reference line of celestial longitude, the sky’s “prime meridian,” the Zero Hour of Right Ascension, just below the left side of Pegasus. It’s daytime so you can’t see the background stars. But for celestial chart-lovers, Monday’s half Moon floats atop all the zero-points.

About The Author

Bob Berman

Bob Berman, astronomer editor for The Old Farmer’s Almanac, covers everything under the Sun (and Moon)! Bob is the world’s most widely read astronomer and has written ten popular books. Read More from Bob Berman

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