The moon's distance from Earth varies significantly throughout its orbit. Understanding this variation is important for astrophotography, tidal predictions, and appreciating phenomena like supermoons.
Orbital Variation
The moon's orbit is elliptical, not circular. Distance varies from about 356,500 km at perigee (closest) to 406,700 km at apogee (farthest). This roughly 50,000 km difference has visible effects on the moon's apparent size and brightness.
Supermoons
A supermoon occurs when a full moon coincides with perigee. The moon appears about 14% larger and 30% brighter than during a full moon at apogee. While the difference is subtle to casual observers, photographers notice the size difference when comparing images.
Tidal Effects
Moon distance directly affects tidal forces. When the moon is closer, its gravitational pull is stronger, resulting in higher high tides and lower low tides. Perigean spring tides (when perigee aligns with full or new moon) produce the most extreme tides.
Focus Implications
For telescope users, moon distance affects focus settings. Astrophotographers may need slight focus adjustments between perigee and apogee to maintain sharpness, especially with long focal lengths.