Supermoon
It is a night when the Moon takes a few steps closer to Earth, shining extra bright and grand like a giant spotlight turned on in the night sky.
Definition A supermoon is an astronomical phenomenon that occurs when a full moon coincides with the Moon's closest approach to Earth (perigee) along its elliptical orbit. Compared to a micromoon (the smallest full moon at apogee), it appears about 14 percent larger in diameter and up to 30 percent brighter.
Why Does the Moon Look Bigger on Some Nights?
Just like a friend walking toward you looks larger and larger, the Moon appears noticeably bigger and more majestic in our night sky when it comes closer to Earth.
The Moon does not orbit Earth in a perfect circle; instead, it travels along a slightly stretched elliptical orbit around Earth. As a result, every month it moves back and forth between its closest and farthest points from us on a regular cycle.
The closest point to Earth is called perigee, and the farthest point is called apogee. When the Moon passes near perigee right as it is fully lit by the Sun, we get to witness an unusually large and bright full moon.
A Closer Look at the Numbers
The term "supermoon" is not an official scientific classification; it was first coined in modern astrology before becoming popular worldwide. In astronomy, it is formally known as a "perigee syzygy." Syzygy describes the alignment of the Sun, Earth, and Moon in a straight line, producing either a full moon or a new moon.
While the average distance between Earth and the Moon is about 384,000 kilometers (around 238,855 miles), at perigee the Moon draws as close as roughly 356,000 kilometers (around 221,000 miles). Conversely, at apogee, it drifts out to nearly 406,000 kilometers (around 252,000 miles).
Due to this 50,000-kilometer gap, compared to the smallest full moon (a micromoon), a supermoon is about 14 percent larger in diameter and 30 percent brighter. Even against an average full moon, it is roughly 8 percent wider and 15 percent brighterโthough comparing yesterday's moon to tonight's with the naked eye alone can still be subtle.
How Does It Affect Earth and the Oceans?
When the Moon draws closer to Earth, its gravitational pull on our planet grows noticeably stronger. This increased gravitational force pulls more strongly on Earth's ocean waters, creating a much larger difference between high tide and low tide than usual.
Periods with the highest high tides and lowest low tides are known as spring tides, and during a supermoon, these swings reach their peak in what are called perigean spring tides. Coastal communities and low-lying areas often issue advisories to prepare for elevated sea levels and coastal flooding during these events.
Rumors occasionally circulate that a supermoon stirs Earth's interior to trigger massive earthquakes or volcanic eruptions. However, scientists analyzing decades of seismic data have confirmed that lunar tidal forces have no proven link to earthquakes or tectonic disruptions.
๐ค Common misconceptions
A supermoon is so overwhelmingly giant that it looks like it covers half the night sky.
A supermoon is roughly 14 percent larger than the smallest micromoon and only about 7 to 8 percent larger than an average full moon. Without nearby horizon landmarks or side-by-side comparisons, the size difference can be tricky to spot with the naked eye alone.
A supermoon triggers catastrophic natural disasters like giant earthquakes and tsunamis.
While the Moon's gravitational pull does raise ocean tides slightly higher, scientific studies have verified that it does not possess enough force to rupture tectonic plates or trigger major earthquakes.
๐งบ Where you meet it
A supermoon is a full moon that coincides with the Moon's closest approach to Earth in its elliptical orbit, making it appear noticeably larger and brighter in the night sky.