Why the Full Moon Appears Closer to Earth

The Moon's Elliptical Orbit

The Moon's orbit around Earth is not a perfect circle but an ellipse. This means that there are points in its orbit where it is closer to Earth—perigee—and points where it is farther away—apogee.

The Perigee and Apogee

When the Moon is at perigee, it can appear larger and brighter in the sky. These visual effects are particularly noticeable when a full moon occurs near perigee, often referred to as a super moon. However, it's important to note that the Moon's distance from Earth does not fundamentally change just because it's a full moon. A super moon is simply a full moon that coincides with the Moon's closest approach to Earth.

The Non-Synchronous Nature of Full Moon and Perigee

The time of the full moon and the perigee shifting are not synchronized. The part of the Moon's orbit that is closest to Earth shifts around the Earth on a 9-year cycle. This means that the Moon gets closest to us three or four times a year, as the Earth completes 9 orbits around the Sun, while the Moon's closest point to Earth drifts.

Understanding the Moon Illusion

The apparent movement of the Moon towards us during a full moon is often attributed to the moon illusion. This phenomenon occurs because the brain interprets objects near the horizon as larger than those higher in the sky, regardless of their actual distance. This is why a full moon on the horizon appears larger than one overhead, even though both are equidistant from Earth.

Frequently Asked Questions

Does the Moon Move Closer to Earth During a Full Moon?

During a full moon, the Moon's distance to Earth does not change. The apparent increase in size is due to the Moon's position in its elliptical orbit, specifically when it is at perigee (closest point to Earth). However, the Moon only reaches this closest point to Earth three or four times a year, not every full moon.

Why Does the Moon Appear Larger on the Horizon?

The moon illusion is a common phenomenon where the Moon appears larger on the horizon compared to when it's higher in the sky. This is due to the brain's perception, not the actual distance of the Moon. The human brain mistakenly judges the size of objects based on their background, making distant objects (like the horizon) relative points of reference, thus creating the illusion of size increase.

How Often Does a Super Moon Occur?

A super moon happens approximately once every three and a half months, or more precisely, it occurs when a full moon coincides with the Moon being in perigee. These events provide a dramatic visual effect, making the Moon appear significantly larger in the sky.

In conclusion, the apparent closeness of the full Moon is due to its elliptical orbit and the way our brain interprets size and distance. The Moon only gets as close to Earth three or four times a year, not at every full moon, as the Earth orbits the Sun and the Moon's orbit slowly shifts. Understanding these phenomena helps explain why the full Moon can appear so spectacular at times.