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Moon that’ll cover sun on August 21 is called a Black Moon

Like Blue Moon, Black Moon is a name from folklore. It’s the name for the 3rd of 4 new moons in a season. The August 21 total solar eclipse is caused by such a moon. Some will call it a Black Moon eclipse.

Composite image of a 2006 solar eclipse by Fred Espenak.  Read his article on the August 21, 2017 total solar eclipse, first one visible from contiguous North America since 1979.

The next solar eclipse will be total and visible from North America. It’ll be the first total solar eclipse visible from contiguous North America since 1979. Read more about the August 21, 2017 total solar eclipse. Composite image of a 2006 solar eclipse by Fred Espenak.

The moon turns new on August 21, 2017 at 18:30 UTC. Some will call it a Black Moon, for a reason entirely unrelated to eclipses. More about that below. A moon at the new phase comes most nearly – for any particular month – to passing between the Earth and sun. This August, 2017 new moon makes that pass directly over the sun’s face, causing the much-anticipated August 21 total solar eclipse . On that day, the day of the coming new moon, the moon will pass between the sun and Earth. The moon’s shadow will fall on Earth. Those in the shadow’s path will witness the solar eclipse, a beautiful sight in the sky, and a dramatic turning of day to dark in the middle of the day.

So … Black Moon. Black Moon eclipse. Why that name? The moon will, of course, in this total solar system and all total solar eclipses appear black in front of the sun’s face during the brief minutes of totality. But that’s not why. In this case, Black Moon stems from folklore, that is, from traditional beliefs, customs, and stories of a community. Prior to the internet, these names were passed by word of mouth. Black Moon is similar to Blue Moon, which, by one definition, can be the third of four full moons in a season. Black Moon is the name used for the third of four new moons in one season, with a season being the period of time between a solstice and an equinox (or vice versa).

Enter your zip code to learn how much eclipse you’ll see, and what time

Most of the time, there are only three new moons in one season. But if the first new moon comes early enough in the season, it’s possible for a fourth new moon to sneak in before that season comes to an end. That’s exactly what happens during the Northern Hemisphere summer (Southern Hemisphere winter) of 2017:

2017 Jun 21: June solstice
2017 Jun 24: new moon
2017 Jul 23: new moon
2017 Aug 21: new moon
2017 Sep 20: new moon
2017 Sep 22: Sept equinox

A Black Moon by the seasonal defintion occurs 7 times in 19 years. EarthSky’s Bruce McClure has more to say about it, over in our daily Tonight pages.

A new moon is more or less between the Earth and sun. Its lighted half is turned entirely away from us. This simulation of a new moon is via memrise.com.

Of course, all new moons are, essentially, black from our earthly perspective. New moons come once each month, as the moon orbits Earth. On the day of new moon – unless we’re viewing a total solar eclipse, we don’t see the new moon. That’s because a new moon rises when the sun rises. It sets when the sun sets. It crosses the sky with the sun during the day. Its fully illuminated face, or day side, is turned entirely away from us.

Modern techniques – telescopes, filters, photography – have made it possible to see the moon even at the instant it becomes new.

That’s the case with Thierry Legault’s image, below, which he acquired in 2013. Read more about Thierry’s image here.

View larger. | Youngest possible lunar crescent, with the moon's age being exactly zero when this photo was taken — at the precise moment of the new moon - at 07:14 UTC on July 8, 2013.  Image by Thierry Legault.  Visit his website.  Used with permission.

Youngest possible lunar crescent, with the moon’s age being exactly zero when this photo was taken — at the instant of new moon – 0714 UTC on July 8, 2013. Image by Thierry Legault. Visit his website.

It’s only as the moon moves in orbit, as its lighted hemisphere begins to come into view from Earth, that we can see it in our sky. Then we see the moon in the west after sunset as a slim waxing crescent – what some call a young moon.

From the U.S. – with autumn approaching – most of us won’t see the young moon again until August 23. It’ll be in the evening sky on August 22, too, but – with the angle of the ecliptic, or sun’s path, slanting low at this time of year with respect to the evening horizon – it’ll be hard to see.

Still, especially if you’re traveling back from the path of totality on August 22 or 23, watch for the young moon. You might catch it along some country highway, in the west shortly after sunset!

By August 23, it should be fairly easy to see the young moon in the west after sunset. The waxing crescent moon shines in the vicinity of Jupiter (and the star Spica) for several days, centered on or near August 25. Read more.

As the moon orbits Earth, it changes phase in an orderly way. Follow these links to understand the various phases of the moon.

Four keys to understanding moon phases

Where’s the moon? Waxing crescent
Where’s the moon? First quarter
Where’s the moon? Waxing gibbous
What’s special about a full moon?
Where’s the moon? Waning gibbous
Where’s the moon? Last quarter
Where’s the moon? Waning crescent
Where’s the moon? New phase

Total eclipse of the sun: August 21, 2017

Moon in 2017: Phases, cycles, eclipses, supermoons and more

Deborah Byrd

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