Essence

A supermoon is a full Moon that occurs near the Moon’s closest point to Earth in its oval path. The Moon’s orbit is elliptical, so its distance from Earth changes: perigee (closer, about three hundred and sixty three thousand kilometres) and apogee (farther, about four hundred and five thousand kilometres). When a full Moon happens near perigee—an alignment called perigee–syzygy—the Moon looks larger and brighter than an average full Moon.

How it differs in the sky (mixed format)

• Apparent size: up to about fourteen percent larger than a far-away full Moon.
  
• Brightness: up to about thirty percent brighter, mainly because it is closer.
  
• Tides: can slightly amplify the usual spring tides, creating perigean spring tides. On normal days this is modest, but during storms coastal flooding risk can rise a little.
  
• How often: usually three to four times a year, depending on how close to perigee one sets the cut-off.
  
• Best viewing: soon after Moonrise or before Moonset on the horizon, when buildings or trees give a sense of scale.
  

Key terms
Elliptical orbit; Perigee; Apogee; Syzygy; Perigean spring tide; Apparent magnitude.

Exam hook

Key takeaways

• A supermoon is a full Moon near perigee.
  
• It appears larger and brighter and can slightly enhance high tides.
  
• It is a regular orbital effect, not a rare omen.
  

UPSC Prelims (MCQ)
Q. Consider the following statements about a supermoon:

1. It occurs when a full Moon coincides with the Moon’s perigee.
   
2. It always causes severe coastal flooding.
   
3. It appears larger mainly because the Moon is closer to Earth.
   Correct answer: 1 and 3 only.
   

One-line wrap
A supermoon is simply the full Moon seen up close on its oval journey—bigger, brighter, and perfectly natural.