What Is a Black Moon? July Set for Thunder Moon, Partial Lunar Eclipse and Black Moon—All You Need to Know

July is set to be a stellar month for skywatchers with the arrival of both a so-called "black moon" and a "thunder moon."

Because the lunar phases do not synchronize perfectly with the widely used Gregorian calendar, every 32 months or so, two new moons—the opposite of a full moon—appear in a single calendar month. The second of these is sometimes referred to as a "black moon," although this is not an official astronomical term.

The opposite of a black moon is a "blue moon"—when two full moons appear in a single calendar month.

New moons occur when the Moon is located between the Earth and the Sun so that the side being lit up by our star is facing away from us. At these times, it is very difficult to see the Moon with the unaided eye.

This year, the first new moon of the month occurred on July 2 at 3:16 p.m. EDT, while the second will take place at at 11:12 p.m on July 31, according to the Old Farmer's Almanac.

The full moon in July—which this year occurs on July 16 at 5:38 p.m. EDT—is traditionally referred to as the "Thunder Moon" or sometimes the "Full Buck Moon."

These names—which originate from Native American tribes—refer to the fact that thunderstorms are frequent in North America in July, and the fact male deer, or bucks, experience a rapid growth of their antlers at this time.

Full moons occur roughly every once a month when the Earth is positioned between the Sun and the Moon. In this situation, the face of the Moon that we can see is fully lit up by our star, appearing like a perfect circle.

The Thunder Moon this year will also coincide with a partial lunar eclipse, however, this will not be visible to those in North America unfortunately. Partial lunar eclipses occur when the Moon passes through Earth's shadow (umbra) which plunges parts of it into darkness. At maximum eclipse—set to take place at 17:30 EDT—around half of the Moon will be obscured by the shadow, appearing black.

Yesterday, hundreds of thousands of people across South America were treated to a spectacular sight as a total solar eclipse was visible from certain parts of Chile and Argentina, Reuters reported.

Unlike lunar eclipses, total solar eclipses occur when the Moon passes directly between the Sun and the Earth, casting a shadow over certain parts of the planet.

partial lunar eclipse
A picture shows the moon during a partial lunar eclipse as seen from Kuwait City on August 7, 2017. YASSER AL-ZAYYAT/AFP/Getty Images