The full moon on October 7, visible across Brazil, will occur at 00:47 AM Brasília time, at about 361,458 km from Earth, closer than the average 384,400 km. Astronomers disagree on classifying it as a supermoon due to the lack of a unified scientific definition. The phenomenon, occurring when the moon is near perigee, promises a spectacle visible all night if the sky is clear. Three potential supermoons are expected in 2025, with the November 5 event being the most widely accepted under stricter criteria.
The term supermoon, coined in 1979 by astrologer Richard Nolle, refers to a full moon within 90% of perigee, the point of closest approach to Earth. However, this percentage is considered arbitrary by experts. The moon’s elliptical orbit causes its distance to vary, affecting its apparent size in the sky.
- Varied criteria: Some define a supermoon as within 360,000 km; others focus on the time interval with perigee.
- Visibility: The full moon rises in the east at sunset and remains visible all night.
- Observation: Clear weather conditions are essential to enjoy the phenomenon.
Supermoon definition under debate
The lack of scientific consensus on the term supermoon leads to different interpretations. Astronomer Josina Nascimento from the National Observatory notes that the concept lacks a solid scientific basis, serving more as a tool for astronomy outreach.
The International Astronomical Union does not set a specific distance for classifying the phenomenon. Thus, institutions and astronomers adopt their own criteria, such as proximity within 360,000 km or temporal alignment with perigee.
Characteristics of the lunar phenomenon
The moon’s elliptical orbit causes its distance from Earth to vary by up to 14%. At perigee, the moon appears slightly larger and brighter, with about 30 minutes of arc in the sky.
This variation, however, is hard to notice with the naked eye without direct comparison. Photos taken at perigee and apogee, months apart, reveal the size difference.
Astronomer Gabriel Hickel from UNIFEI explains that a supermoon is only noticeable in comparative images. He notes that a full moon at perigee stands out for being visible all night.
The moon’s apparent size is measured in degrees, minutes, and seconds of arc, with an extended pinky finger equating to 1 degree in the sky.
Supermoons expected in 2025
In 2025, up to three full moons may be considered supermoons, depending on the criteria. The November 5 event, at 356,980 km and within 9 hours of perigee, is the most accepted.
The December 4 full moon, at 357,219 km, may also qualify as a supermoon for some. The October 7 event, at 361,458 km, is debated for falling outside stricter criteria.
The phenomenon occurs due to the moon’s alignment with the sun, fully illuminating its visible face.
How to observe the October full moon
Choose locations with low light pollution to enjoy the event. The moon will rise in the east at sunset and set in the west at sunrise.
Binoculars or telescopes can enhance details of the lunar surface, such as craters.
Visual difference of a supermoon
A supermoon is about 7% larger and 15% brighter than a regular full moon, but the difference is subtle. According to Hickel, direct comparison with an apogee moon, through photos, highlights the apparent size increase.
The popularization of the term supermoon boosts public interest in astronomy, despite scientific disagreements. The next opportunity to observe the phenomenon will be in November, with even more favorable conditions.