What Is a Supermoon and When Is the Next One?
When's the Next Super Moon?
2021 will see two Super Full Moons—on April 26/27 and May 26.
If the weather cooperates in your location, Full Moons make for spectacular photographs, especially when the Moon is close to the horizon. Use our Moon photography tips to capture it with your camera or smartphone.
There will also be two Super New Moons in 2021. The first takes place on November 4/5 and the other on December 3/4, depending on your time zone. The Super New Moons, like any other New Moon, won't be visible from Earth, but the dark night skies will provide great opportunities for some great night sky watching, especially around December 4 when the Geminids start becoming active. There is also a total solar eclipse on December 4, 2021, visible from Antarctica.
Super Full and New Moon
When a Full Moon takes place when the Moon is near its closest approach to Earth, it is called a Super Full Moon. When there is a New Moon around the closest point to Earth, it is known as a Super New Moon.
Perigee and Apogee
A New Moon at perigee is also often referred to as a supermoon. However, this event usually garners less attention because a New Moon is invisible from Earth.
The Moon's orbit around Earth is not a perfect circle, but elliptical, with one side closer to Earth than the other. As a result, the distance between the Moon and Earth varies throughout the month and the year. On average, the distance is about 382,900 kilometers (238,000 miles).
Not an Official Name
Supermoon is not an official astronomical term. It was first coined by an astrologer, Richard Nolle, in 1979. He defined it as ‘a New or a Full Moon that occurs when the Moon is at or near (within 90% of) its closest approach to Earth in its orbit’. It is not clear why he chose the 90% cut off in his definition.
There are no official rules as to how close or far the Moon must be to qualify as a Supermoon or a Micro Moon. Different outlets use different definitions. Due to this, a Full Moon classified as a Supermoon by one source may not qualify as a Super Full Moon by another.
The following definitions are used at timeanddate.com:
- Supermoon: A Full or New Moon that occurs when the center of the Moon is less than 360,000 kilometers (ca. 223,694 miles) from the center of Earth.
- Micromoon: A Full Moon or New Moon that takes place when the center of the Moon is farther than 405,000 kilometers (ca. 251,655 miles) from the center of Earth.
A Super Full Moon's angular size is 12.5%–14.1% bigger than a Micro Full Moon, and 5.9%–6.9% bigger than an average Full Moon (in years 1550–2650).
Technical Name: Perigee-syzygy
The technical term for a Supermoon is perigee-syzygy of the Earth-Moon-Sun system. In astronomy, the term syzygy refers to the straight-line configuration of three celestial bodies. Another name is perigee Full Moon.
Looks Bigger and Brighter
Because it's so close to Earth, a Super Full Moon also looks about 30% brighter than a Micro Full Moon and about 16% brighter than an average Full Moon.
Moon Illusion: Best at Moonrise and Moonset
The best time to enjoy a Super Full Moon, or any other Full Moon, is just after moonrise, when the Moon is close to the horizon. Just before moonset is also a good time.
When the Full Moon is low, it looks bigger and brighter than when it's higher up in the sky. This is called the Moon illusion, and actually makes more of a difference to what it looks like than the real boost you get from it being a bit closer to Earth.
Higher Tides at Supermoon
The greatest difference between high and low tide is around Full Moon and New Moon. During these Moon phases , the gravitational forces of the Moon and the Sun combine to pull the ocean’s water in the same direction. These tides are known as spring tides or king tides.
Supermoons lead to around 5 cm (2 inches) larger variation than regular spring tides, called perigean spring tides.
The tidal range is smallest during the two Quarter Moons, known as neaps or neap tide.
Natural Disaster Trigger?
Although the Sun and the Moon’s alignment cause a small increase in tectonic activity, the effects of the Supermoon on Earth are minor. Many scientists have conducted studies, and they haven’t found anything significant that can link the Super Moon to natural disasters.
According to NASA, the combination of the Moon being at its closest and at Full Moon, should not affect the internal energy balance of the Earth since there are lunar tides every day.