Sky watch: 'Harvest' moon same as other times of year

When the full moon rises at sunset on Sept. 22, many will be watching.

"Why?" you may ask. Because it's the annual harvest moon, and people tend to think that this is different from all other full moons of the year.

Some believe it appears larger and redder, but this isn't true. Like the sun, the moon always appears redder when rising since its light must pass through a greater path of atmosphere on its way to our eye.

As for its apparent immensity, it's no different from any other time we see the moon near the horizon. Its size is an optical trick known as the moon illusion.

The "harvest" moon is a name given to the full moon closest to the autumnal equinox - the beginning of autumn; this year, that also occurs on Sept. 22.

It's still pretty impressive. Even the unaided eye or binoculars will reveal that the lunar surface is not uniformly bright but, instead, has a mottled appearance.

We know the lighter areas of our moon as mountainous or heavily cratered terrain of generally higher elevation, and we call them the lunar highlands.

The darker areas are roughly circular in shape and cover much of the moon's face. Some ancient sky watchers believed these were lunar oceans, and named them "mare" or "seas," a name they still carry, even though we know the moon is a dry and barren world.

We now know the mare as large plains of solidified lava that welled up from deep inside the moon during its early evolution and flooded the lowlands. Many of these features still carry the poetic names of antiquity: the Sea of Serenity, Ocean of Storms and more.

Perhaps most famous is the Sea of Tranquillity, made famous by the Apollo XI mission, which landed the first man on the moon. It appears near the westernmost side and near the top of the rising moon.

Now, maybe this science stuff will add to your appreciation of the harvest moon. Regardless, on the afternoon of Sept. 25, grab a picnic dinner and blanket, and head to a hilltop with a view toward the east.

If the sky is clear, I promise you'll enjoy the show!