July 4th Full Buck Moon Will Feature a Lunar Eclipse

This Fourth of July, a full moon will grace the night skies and a faint lunar eclipse will also be visible from all of the United States.

Lunar eclipses only occur when the moon is full, meaning when the Earth is located directly between the sun and our natural satellite.

Technically, this happens roughly once month at a specific moment in time—which in this case is 12:44 a.m. EDT, July 5, or 9:44 p.m. PDT, July 4. However, the moon will appear full to most observers for about a day either side of this instance.

The moon will rise in the east after sunset on July 4, and will be visible in the sky fully illuminated—appearing like a perfect circle—until dawn.

In North America, the full moon in July is often referred to as the "Full Buck Moon"—a name that derives from the fact that as summer peaks, the velvety antlers of male deers, which first appear in early spring, finish growing, forming pointed tips and hardening, according to the Farmer's Almanac.

It also sometimes called the "Full Hay Moon" because at this time of year, farmers cut and cure hay to store for winter feed. The month's frequent thunder storms also mean the July full moon is also called the "Full Thunder Moon."

As this July full moon drifts through the night sky, a "penumbral lunar eclipse" will be visible in many parts of the world, including most of North America, South America, southern and western Europe, and much of Africa.

These eclipses occur when the moon passes through the more diffuse part of the Earth's shadow, known as the penumbra. When this happens, the moon, or parts of it, may appear slightly darker than usual.

penumbral lunar eclipse
The full moon is seen during a penumbral lunar eclipse in Mexico City on June 5, 2020. RODRIGO ARANGUA/AFP via Getty Images

This effect is very subtle, to the point of sometimes being imperceptible to the untrained eye. Nevertheless, eagle-eyed observers may, at best, notice a small segment of the moon darkening slightly between 11:07 p.m. EDT on July 4 and 1:52 a.m. EDT on July 5 when the eclipse begins and ends.

"A penumbral lunar eclipse happens when our moon is 'kissed' only marginally by the most external regions of the structure of the Earth's shadow," astronomer Gianluca Masi, from the Virtual Telescope Project, told Newsweek.

The best time to view the event is peak eclipse at around 12:30 a.m. EDT, July 5, when roughly a third of the moon's surface will be covered by the penumbra, local weather permitting.