Supermoon

A supermoon is a term used to describe the phenomenon when a full moon coincides with the Moon’s closest approach to Earth in its elliptical orbit, resulting in a larger and brighter appearance than a typical full moon. This event is scientifically referred to as a perigee-syzygy of the Earth–Moon–Sun system, where “perigee” refers to the Moon’s closest point to Earth and “syzygy” denotes the alignment of the three celestial bodies. The term “supermoon” is not an astronomical term but rather an astrological one popularised in recent decades to describe this visually striking event.

Astronomical Background

The Moon orbits Earth in an elliptical path with an average distance of about 384,400 kilometres. Its distance from Earth varies from approximately 356,500 kilometres (perigee) to 406,700 kilometres (apogee). When a full moon occurs near the perigee, it appears around 14% larger and 30% brighter than a full moon at apogee. This optical enhancement is primarily due to the Moon’s proximity rather than any intrinsic change in its luminosity.
The cycle of the Moon’s phases takes about 29.53 days, known as a synodic month, while the perigee-apogee cycle takes about 27.55 days. The coincidence of these two cycles results in periodic supermoons, typically occurring three to four times a year.

Terminology and Origin

The term “supermoon” was coined in 1979 by astrologer Richard Nolle, who defined it as a new or full moon occurring when the Moon is within 90% of its closest distance to Earth. Though not an officially recognised astronomical term, it has gained widespread acceptance in popular culture, scientific communication, and media reporting due to its visual and emotional appeal.
Astronomers prefer to use the technical term perigee full moon, which accurately conveys the geometric and orbital mechanics involved. Despite the difference in terminology, both expressions refer to the same physical event.

Types of Supermoons

Supermoons can occur both during full moon and new moon phases:

• Full Supermoon: When the Moon is fully illuminated and closest to Earth, creating a strikingly bright and large appearance visible to the naked eye.
• New Supermoon: When the Moon is near perigee but aligned between the Earth and the Sun, rendering it invisible to observers on Earth; however, its gravitational effects are still felt.

Among these, full supermoons are the most observable and commonly discussed in the public domain.

Visual and Tidal Effects

The most notable impact of a supermoon is its visual enhancement, where it appears larger and brighter in the night sky. This perceptual difference is most evident when the Moon is near the horizon, producing the “Moon illusion”—an optical effect where the Moon appears larger due to comparison with terrestrial objects.
Supermoons also have gravitational effects on Earth, contributing to higher-than-average tides, known as perigean spring tides. During this period, the combined gravitational pull of the Moon and Sun slightly increases the tidal range, leading to higher high tides and lower low tides. Although these effects are generally minor, they can exacerbate coastal flooding in vulnerable regions during storm surges.

Frequency and Notable Occurrences

Supermoons occur several times each year, though not all are equally spectacular. The magnitude of the event depends on the exact distance of the Moon at perigee and its alignment with the Earth and Sun.
Some of the most remarkable supermoons include:

• 14 November 2016: The largest since 1948, when the Moon came within 356,511 kilometres of Earth.
• 26 May 2021: Coincided with a total lunar eclipse, creating the rare “super blood moon.”
• 31 August 2023: Featured a blue supermoon, the second full moon in a single month, making it both a supermoon and a blue moon.

Cultural and Scientific Significance

Throughout history, lunar phenomena have held deep cultural and symbolic meaning across civilisations. Supermoons are often associated with myths, rituals, and agricultural calendars, with many societies viewing them as signs of change or renewal. In modern times, they have become opportunities for astronomical education, photography, and public engagement with science.
Scientists also use supermoons to refine models of lunar motion and study the Earth–Moon gravitational relationship. Observations made during perigee events help calibrate instruments measuring lunar distance and surface reflectivity.

Misconceptions and Criticism

Despite their popularity, supermoons are sometimes surrounded by misconceptions. The apparent size difference is often exaggerated in media representations, leading to unrealistic expectations. Scientifically, the variation is subtle to the naked eye and can be difficult to discern without photographic comparison.
Some astronomers criticise the term “supermoon” as being sensationalist, arguing that it distorts public understanding of basic lunar mechanics. Nonetheless, it remains a useful tool for raising public interest in astronomy and encouraging observation of celestial events.

Observation and Photography

Observing a supermoon requires no special equipment, though clear skies and minimal light pollution enhance visibility. Photographers often use the opportunity to capture dramatic images by juxtaposing the enlarged Moon with terrestrial landmarks. Using telephoto lenses and timing the observation near moonrise or moonset can accentuate the Moon’s perceived size and colour.
For amateur astronomers, the event also provides a chance to study surface features such as lunar maria, craters, and mountain ranges under optimal lighting conditions.