Photo by iStock/alexeys
September is all about the moon, with the convergence of the Full Harvest Moon with perigee and a total lunar eclipse.
A “perigee moon” occurs when the moon is closest to Earth in its month-long orbit. On September 27 at 6:55 p.m. PDT and 9:55 p.m. EDT, the moon is at perigee less than an hour before the apex of the Full Harvest Moon (10:50 p.m. EDT). This is the closest coincidence of perigee moon and full moon for the year. In recent years when perigee and a full moon occur on the same date, it's been dubbed a Supermoon by many news sources.
The Full Harvest Perigee Moon has more in store for observers than just being big and bright. A total lunar eclipse will begin on September 27 as well. It will be visible to all of North America but more so for those in the eastern half, who will get to see the eclipse in its entirety. If you're east of a line extending from western Minnesota south to Houston, the moon will be above the horizon as the eclipse starts. In Chicago, for example, the eclipse begins Sunday, September 27 at 7:11 p.m., peaks at 9:47 p.m. and wanes by 12:22 a.m. Monday morning.
For those in western states like California and Washington, where wildfires have been rampant, the soot in the air may change the appearance of the lunar eclipse, making it darker or possibly more violet, depending on the amount and type of aerosols and how they filter the view.
September also brings the start of autumn. Earlier sunsets mean after-dinner walks and runs will end in the dark. On September 23, the sun stands over the equator at 1:22 a.m. PDT. A few hours later the sun rises directly in the east and then that evening, sets directly in the west. For many cities in the United States, September begins with around 13 hours of daylight and ends with less than 12 hours. Longer nights will predominate until March brings the spring equinox.
A partial solar eclipse occurs on September 13, 2015, visible only to those in southern Africa and Antarctica. Up to ninety percent of the sun will be hidden in Antarctica, but only forty percent in more populous areas such as South Africa.
Many of the planets hover close to the sun in September. Venus and Mars become morning objects, visible just before sunrise. Jupiter is too close to the sun to be visible, but Mercury is low above the horizon after sunset. It will be the closest planet to the sun this month, and one of the better dates to try to catch sight of it is September 15, when a very slender crescent moon is above the horizon just after sunset. Mercury will be shining at magnitude 0.8 to the lower right. You may also be able to see the star Spica, at magnitude 1, to the moon’s lower left.
Saturn is the best bright planet to view in September. On September 18, the waxing moon is less than three degrees from the Ringed Planet. Saturn is in the south after sunset, but even it sets early, following the sun and leaving the sky bereft of bright planets.
Neptune reaches opposition on September 1, when it rises opposite the sun and sets at sunrise. But Neptune is a dim magnitude 7.8, requiring binoculars or a telescope to spot, and it’s not near any bright signposts, making it very difficult to pick out among a sea of background stars.