Sky ArchiveTonight

Waxing gibbous moon this week

Waxing gibbous moon on November 12, 2016 via OMladyO in Switzerland.

Tonight – July 31, 2017 – and in the coming evenings, people will see a waxing gibbous moon in the evening sky. The half-lit first quarter moon just happened on Sunday, July 30. Waxing means we’re seeing more and more of the moon’s illuminated side, or day side. Gibbous means the moon’s disk appears to us now as more than 50% lit by sunshine. On July 31, the moon is barely more than 50% illuminated, but the moon will be appearing bigger and brighter each evening this week. Click here to know the moon’s present phase.

Full moon will come August 7 or 8, 2017, depending on your time zone. And thus, in 2017, the moon will all but obliterate the annual Perseid meteor shower. At the same time, the moon is now edging toward a lunar eclipse, then a solar eclipse. 

At this upcoming full moon, people from Earth’s Eastern Hemisphere can watch Earth’s dark shadow (umbra) darken the southern edge of the August 2017 full moon. Hence that part of the world will see a partial eclipse of the moon.

Click here to learn more about the August 7-8 lunar eclipse.

Earth’s dark shadow (umbra) clips the southern part of the moon on the night of August 7-8. The moon goes through the Earth’s shadow from west to east. This lunar eclipse is not visible from North America.

By the way, a lunar eclipse can only happen at full moon because that’s the only time Earth’s shadow can fall on the moon. More often than not, the full moon eludes the Earth’s shadow by swinging to the north or south of it, thereby missing being eclipsed. But not this month.

Why no eclipse every full and mew moon?

Three weeks from now, the moon’s shadow will hit Earth at the August 21, 2017 new moon. The moon’s dark umbral shadow will cross the U.S. during daylight hours on August 21, to showcase a total eclipse of the sun.

Total eclipse of sun: August 21, 2017

How to watch a solar eclipse safely

Best places to watch 2017 eclipse

How much traffic on eclipse day?

Path of the total solar eclipse – with partial eclipse percentages indicated – via (used with permission). Click here to enter your zip code and learn more about the solar eclipse in your area.

For now, each day after sunset, you’ll see more of the moon’s disk as sunlit. Another way to say this is, you’ll see more of the moon’s day side. Meanwhile, the dark part of a waxing gibbous moon – the part we can’t see well at this moon phase, because it blends with the dark of our own night, or blue of our own day – is the moon’s night side. Just as on Earth, night on the moon happens to be that part of the moon submerged in the moon’s own shadow. How much of the moon’s night, or day, side is visible from Earth depends on the lunar phase.

As the moon orbits Earth, its changing geometry with respect to the sun produces the characteristic phases. This composite image is a mosaic made from 25 individual photos of the moon and illustrates its phases over one synodic month. For complete details about this image, see Moon Phases Mosaic. Photo copyright Fred Espenak.

Bottom line: The waxing gibbous moon is waxing toward full moon on August 7-8, obliterating the annual meteors showers and edging toward a lunar eclipse, then a solar eclipse. 

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July 31, 2017
Sky Archive

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Bruce McClure

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