If you were camping this past weekend (December 12, 2008) and the sky was clear, it might have seemed that the night was especially well lighted. It wasn’t your imagination. Scientists say that the full moon appeared 14% larger and 30% brighter than normal this past weekend. Why was that?
The moon’s orbit around Earth is not circular, it is elliptical. This means that the moon’s distance from earth varies depending on where it is in the orbit. The closest point of the orbit is the perigee. The point where the moon is farthest from earth is called the apogee. The moon’s average distance from earth is approximately 238,000 miles. On December 12 (the day of the full moon) the moon was also at its perigee, about 222,000 miles form Earth. That’s why the moon seemed larger and brighter.
"It's only every few years that a full moon happens to coincide with the part of the Moon's orbit when its closest to the Earth," said Marek Kukula, an astronomer at the UK's Royal Observatory. In fact the last time this occurred was about 15 years ago.
The gravitational attraction of the moon also affects our oceans. Tides are affected by the pull of the sun and the moon. Tides are also higher when the moon is at its perigee. They are called “perigean tides.”
Some other conditions cause the moon to seem larger or brighter. During moon rise or moon set when the moon is close to the horizon, it appears larger than when it is higher in the sky. "The moon appears largest as it rises and sets, but this is a psychological illusion," Dr Kukula said. “When it's close to the horizon, our brain interprets it as being bigger than it actually is, this is called the moon illusion," In the northern hemisphere the moon sometimes seems brighter in the winter and that is because it is higher in the sky.
Some other interesting moon facts:
- The moon is moving away from the Earth at about 1.6 inches per year.
- When we see a full moon it is not completely full. “For that to happen, all three objects (sun, Earth and moon) have to be in a perfect line, and when that rare circumstance occurs, there is a total eclipse of the moon.” Year's Biggest Full Moon Friday Night, Robert Roy Britt, editorial director, space.com – Thu Dec 11, 1:45 pm ET
- A full moon has not been proven to cause werewolves to go on the prowl.
Hopefully you have learned something about our moon and got an opportunity to enjoy a well lighted campout.