Corn Moon, Neptune At Opposition: September Sky Events To Watch Out For

Excited for another month of sky watching? Here are some of the sky events that sky watchers may not want to miss this September.

Opening the month on Sept. 1 is the expected flyby of asteroid 2011 ES4, a massive Near-Earth Object (NEO) some 50 meters across that will possibly fly within 45,000 miles of the Earth. At this size, 2011 ES4 is about the size of a house and, although it's approach will be quite close to the Earth, it will still pass further away than all the orbiting satellites.

With a brightness magnitude of 26.04, 2011 ES4 will likely only be visible through long-exposure photography.

The day after, on Sept. 2 at 1:22 am EDT, the last full moon of summer will appear opposite the sun. While the moon is technically only full for a few moments, it typically appears full for several days and this month, it will appear full from Monday evening until Thursday morning.

According to The Old Farmer’s Almanac, September's full moon is called a "full corn moon" because it corresponds to the time of the year when staple crops such as corn, pumpkins, beans and wild rice are harvested by the Native Americans.

Typically, the September moon is also the Harvest Moon because it's close to the autumnal equinox but this year, the event will be closer to the October full moon so that will take on the Harvest Moon title instead.

Other names for it include the "Barley Moon," the "Moon When the Deer Par the Earth" and the "Moon When the Calves Grow Hair."

On Sept. 11, Neptune will be at opposition, which means that the blue giant will be at its closest approach to the Earth and its face will be completely illuminated by the Sun. On this day, Neptune will be visible all night long and will be brighter in the sky than at any other time of the year. This makes it the best time of the year to view the blue giant. But because of its extreme distance from the Earth, all but the most powerful telescopes will likely only see Neptune as a blue dot.

The autumnal equinox mentioned earlier will occur on Sept. 22 at 9:30 am EDT. On this day, the Sun will directly shine on the equator and, nearly throughout the world, there will be equal amounts of day and night.

It will be the first day of fall for those in the Northern Hemisphere and the first day of spring for those in the Southern Hemisphere.