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Since the peak of this full moon is less than 10 hours after the Moon was closest to the Earth in its orbit, this will be a supermoon. The term “supermoon” was coined by astrologer Richard Nolle in 1979 and refers to either a new or full moon that occurs when the Moon is within 90% of perigee, its closest approach to Earth.

The Moon will appear full for about three days, from early Tuesday morning through early Friday morning.

Since we can’t see new supermoons (except when the Moon passes in front of the Sun and causes an eclipse), what has caught the public’s attention are full supermoons, as these are the biggest and brightest full moons of the year. Since perigee varies with each orbit, different publications use different thresholds for deciding which full moons qualify, but all agree that this full moon is a supermoon.

Since this is also called the Thunder Moon, a quick note on lightning safety. Most of the lightning that strikes the ground arcs from the negatively charged bottom of the storm to the ground underneath the storm. Much rarer is positive lightning, which arcs from the top of a thunderstorm to strike the ground up to eight miles away. Positive lightning can sometimes strike areas where the sky is clear (hence the term “bolt out of the blue”). Because it arcs across a greater distance it tends to be 5 to 10 times more powerful than regular ground strikes. Because it can strike dry areas outside of the storm, positive lightning tends to start more fires than negative lightning. Although positive lightning is rare (less than 5% of all lightning strikes), the lack of warning combined with its greater power makes it more lethal. A good rule to follow is, that if you can hear the thunder, you can be struck by lightning.

As usual, the wearing of suitably celebratory celestial attire is encouraged in honor of the full moon. Be safe (especially during thunderstorms), avoid starting wars, and take a moment to clear your mind.

A full moon rises over Griffith Observatory in Los Angeles in August 2021. Credit: NASA/Preston Dyches

What’s in a Name

In the 1930s the Maine Farmer’s Almanac began publishing Native American names for full moons. According to this Almanac, the Algonquin tribes of what is now the northeastern United States called this the Buck Moon. Early summer is normally when the new antlers of buck deer push out of their foreheads in coatings of velvety fur. They also called this the Thunder Moon because of early summer’s frequent thunderstorms.

Europeans called this the Hay Moon for the haymaking in June and July, and sometimes the Mead Moon (although this name was also used for the previous full moon). Mead is created by fermenting honey mixed with water, sometimes adding fruits, spices, grains, or hops.

For Hindus, Buddhists, and Jains, this is the Guru Full Moon (Guru Purnima), celebrated as a time for clearing the mind and honoring the guru or spiritual master.

For Theravada Buddhists, this full moon is Asalha Puja, also known as Dharma Day or Esala Poya, an important festival celebrating the Buddha’s first sermon.

As the full moon day of Waso (the fourth month of the traditional Burmese lunisolar calendar), this is the start of the three-month annual Buddhist retreat called Vassa.

In many traditional lunisolar and lunar calendars, full moons fall on or near the middle of the lunar months. This full moon is in the middle of the sixth month of the Chinese calendar, Tammuz in the Hebrew calendar, and Dhu al-Hijjah, the 12th and final month of the Islamic year. Dhu al-Hijjah is the month of the Hajj and the Festival of the Sacrifice, and is one of four sacred months during which fighting is forbidden.

Fast Facts

A supermoon occurs when the Moon’s orbit is closest (perigee) to Earth at the same time the Moon is full. So what’s so special about a supermoon? For the interested observer, there’s plenty to see and learn.

  • The Moon orbits Earth in an ellipse, an oval that brings it closer to and farther from Earth as it goes around.
  • The farthest point in this ellipse is called the apogee and is about 253,000 miles (405,500 kilometers) from Earth on average.
  • Its closest point is the perigee, which is an average distance of about 226,000 miles (363,300 kilometers) from Earth.
  • When a full moon appears at perigee it is slightly brighter and larger than a regular full moon – and that’s where we get a “supermoon.