Beware The Black Moon This Halloween

The moon is right out in front of our faces today, located a few degrees above or north of the sun -- the reason we can't see it ;) Stellarium
This illustration shows the sky looking south around 1 p.m. CDT Sunday Oct. 30. The moon is right in front of our face today, located a few degrees above or north of the sun. We can’t see it of course because of overwhelming daylight. Use your imagination to see the moon in the foreground, some 387 times closer to Earth than the sun, the better to understand why no sunlight touches the side of the moon facing Earth at new phase. Stellarium

As if chased by dark spirits, the moon won’t linger long on Halloween night. The last we heard of its whereabouts was Friday morning, when some of you got to see the sharp-tipped crescent swing by the planet Jupiter at dawn. Shortly after, it slipped out of the picture on its way to new moon phase, which happens today. At new moon, the moon passes almost directly between the Earth and sun, so we “see” it in the daytime sky in the same direction as the sun.  As you might guess, that’s the reason a new moon is invisible, since the glare of daylight blanks it from view. There’s another reason too: the side facing us isn’t illuminated by sunlight, so it’s nearly black. Right now the lunar farside is facing the sun and bathed in sunshine.

This diagram shows how we see the different phases of the moon depending on where the moon is in its orbit (center) in relation to the sunlight that falls on it. Credit: NASA
This diagram shows how we see the different phases of the moon depending on where the moon is in its orbit (center) in relation to the sunlight that falls on it. At new phase, it’s between Earth and the sun and the side facing us is dark because no sunlight reaches there. Credit: NASA

During a partial or total solar eclipse, the lineup of Earth-moon-sun is precise, and we see our satellite pass in front of the sun in silhouette. But during most months, due to the moon’s tilted orbit, it passes a short distance either north or south (above or below) the sun.

Today’s new moon is the second of the month for some. Because the moon is always on the move along its orbit about the Earth, it remains in new phase for only an instant. That instant occurred at 12:38 p.m. Central Daylight Time today. Before 12:38, it was officially in the morning sky and rose before the sun; after 12:38, it transitioned to the evening sky and now sets after the sun.

The last new moon happened on September 30 at 7:11 p.m. (CDT) for North and South American skywatchers, but if you live in Europe and Africa and Asia, it turned new on October 1 at 12:11 a.m. Greenwich Time. Recall that because Europe is east of the U.S., clocks there are ahead of our clocks by four hours (Eastern time) to 7 hours (Pacific). The time difference means that some of you reading this will have two new moons this month. You’ve probably heard of a Blue Moon, defined popularly as the second full moon in a month, but have you come across a Black Moon? Well, you have now — that’s the popular name for the second new moon in a month.

Look for a thin crescent steeped in the pumpkin glow of twilight on Halloween night. Stellarium
Look for a thin crescent steeped in the pumpkin glow of twilight on Halloween night. Stellarium

Like Blue Moons Black Moons are infrequent, happening about once every 2.7 years. The trick to getting one is for the new moon to land on the first day of any month with the exception of February. The time from one new moon to the next (or one full moon to the next) is 29.5 days, which neatly fits into a 30 or 31 day month. Sorry February. Even if the new (or full) moon occurred exactly at midnight on February 1st during a leap year, the next new moon would be 0.5 x 24 = 12 hours after midnight on February 29 or March 1. No getting around it, Valentine’s month is both blueless and blackless.

On Halloween evening, if you plan well, you just might bag a lunar treat. Skywatchers living in the central and southern U.S. will glimpse a fresh, new crescent only a few degrees (two fingers held at arm’s length) above the western horizon 20-30 minutes after sunset. Those living in the northern states and southern Canada will see it even lower or not at all. The moon’s path at crescent phase this time of year keeps it close to the horizon, making it a challenge to see until it fills out and moves farther from the sun in the coming nights.

Wishing you a starry, scary and darkly magical Halloween!

*** Want to learn more about the phases of the moon? My new book, Night Sky with the Naked Eye, will publish on Nov. 8, but you can pre-order right now at these online stores. Just click an icon to go to the site of your choice – Amazon, Barnes & Noble or Indiebound. It’s currently available at the first two outlets for a very nice discount:

Night Sky book cover Amazon anno
Night Sky book cover BN

Night Sky book cover Indie