Full Moon is really BIG and BRIGHT in October

William Atkins
Wednesday, 24 October 2007 20:05

Science - Space

On Thursday night, October 25, and into Friday morning, October 26, 2007, the Moon will be visually much larger and brighter than usual.      

In fact, according to NASA's SpaceWeather.com, it is expected to be about 14 percent wider and around one-third brighter than an average full Moon. It will be the biggest full Moon seen during the year. Of course, the Moon does not actually change sizes. It only “appears” larger. Why? Please, read below.

The reason why this full Moon is larger and brighter than usual is because we are seeing the Moon near its closest approach to the Earth. What is called a ‘perigee Moon’. This apparent size difference occurs because the orbit of the Moon about the Earth is ellipical in shape.

Its closest approach (perigee) is approximately 226,600 miles (363,104 kilometers), while its furthest point on its orbit (apogee) about the Earth is about 252,100 miles (405,696 kilometers). This results in a difference of about 25,500 miles. Its average distance from the Earth is around 239,000 miles (384,600 kilometers).

Thus, this visually larger full Moon is possible because the Moon seen on October 25-26 is actually about 25,000 miles closer than when it is seen at its furthest point away from the Earth.

The orbital period of the Moon from perigee to apogee and back to perigee is called the anomalistic month.

As a side note, the distance between the Moon and the Earth has just been measured to an accuracy of one millimeter. (See “APOLLO measures Moon distance to 1 millimeter; also helps with gravity”.)

With Halloween coming up and the Moon looking bigger than usual, Thursday night would seem to be a good time to look up in the evening sky and really howl at the Moon.