On Sunday night, September 27th, for the fourth time in the last 17 months, the Moon will once again become completely immersed in the Earth’s shadow, resulting in a total lunar eclipse.
As is the case with all lunar eclipses, the region of visibility will encompass more than half of our planet. Nearly a billion people in the Western Hemisphere, nearly a billion and a half for much of Europe and Africa, and perhaps another half billion in Western Asia, will be able to watch as the full Harvest Moon becomes a shadow of its former self and morphs into a glowing coppery ball.
It will also be the biggest full Moon of 2015, since on the very same day, the Moon will also be at perigee — its closest point to the Earth at 221,753 miles (356,877 km) — making it a so-called “supermoon.”
Almost everyone in the Americas and Western Europe will have a beautiful view of this eclipse. The Moon will be high in a dark evening sky as viewed from most of the United States and Canada while most people are still awake and about. The only problematic area will be in the western quarter of the United States and west-central Canada, where the first partial stage of the eclipse will already be under way when the Moon rises and the Sun sets on Sunday evening. But if you have an open view low to the east, even this situation will only add to the drama, for as twilight fades, these far-westerners will see the shadow-bitten Moon coming into stark view low above the landscape. And by late twilight, observers will have a fine view of the totally eclipsed lunar disk glowing red and dim low in the eastern sky.
Alaskans will also see the Moon rise during the eclipse; in fact, much of eastern Alaska will see the Moon rise while completely immersed in the Earth’s shadow. For Hawaiians, moonrise unfortunately come after the end of totality, with the Moon gradually ascending the sky and its gradual emergence from the shadow readily visible. Western Europe and Africa also will get a good view of the eclipse, but at a less convenient time: before dawn on Monday morning, September 28.
Here’s the reason for the ruddy coloration during totality: If you were an astronaut on the Moon during the eclipse, you would be seeing the Earth move in front of the Sun. Since the Moon shines by reflected sunlight, you would think that once the Earth completely covers the Sun that the lunar landscape would be plunged into complete darkness. But that does not happen because when the Sun is completely hidden, a reddish ring of light appears to surround the disk of the Earth. That light is our atmosphere being backlit by the Sun. The reddish color is the same color that we see each day at sunrise and sunset; so during totality we are seeing the combined light of all of the sunrises and sunsets occurring around our globe that is dimly lighting up the surface of the Moon during the total eclipse.
At mid-totality, the darkness of the sky is very impressive. Faint stars, which were completely washed-out by the brilliant moonlight prior to the eclipse, become visible and the surrounding landscape takes on a somber hue. During totality, the Moon appears anywhere from 10,000 to 100,000 times dimmer than before the eclipse began. As totality ends, the eastern edge of the Moon begins to emerge from the umbra, and the sequence of events repeats in reverse order until the spectacle is over.
Unless airborne volcanic aerosols or other unusual atmospheric effects influence its appearance, the Moon’s disk should appear moderately bright, especially right around the beginning and end of totality. The lower part of the Moon will likely appear brightest and glowing a ruddy or coppery hue, while the upper half of the Moon should look more gray or chocolate color.
The eclipse will actually begin when the Moon enters the faint outer portion, or penumbra of the Earth’s shadow. The penumbra, however, is all but invisible to the eye until the Moon becomes deeply immersed in it. Sharp-eyed viewers may get their first glimpse of the penumbra as a delicate shading on the left part of the Moon’s disk about 20 minutes before the start of the partial eclipse (when the round edge of the central shadow or umbra, first touches the Moon’s left edge). During the partial eclipse, the penumbra should be readily visible as a dusky border to the dark umbral shadow.
The Moon will enter Earth’s much darker umbral shadow at 1:07 on September 28 by Greenwich or Universal Time, which is 9:07 p.m. on September 27 in the Eastern Time Zone, 8:07 p.m. Central Time, 7:07 p.m. Mountain Time and 6:07 p.m. Pacific Time (before moonrise). Sixty-four minutes later the Moon is entirely within the shadow, and sails on within it for 72 minutes until it begins to find its way out at the lower left (southeastern) edge.
The Moon will be completely free of the umbra by 9:27 p.m. Pacific Time or 12:27 a.m. (September 28) Eastern Time. The vaguer shading of the inner penumbra can continue to be readily detected for perhaps another 20 minutes or so after the end of umbral eclipse. Thus, the whole experience ends toward 1:00 a.m. for the East (with the re-brightened Moon now sloping down along the arc it describes across the sky) or during the mid-evening hours for the West.
For Europe and Africa, the mid-point of this eclipse occurs roughly between midnight and dawn on the morning of September 28 and as such the Moon will still be well placed in the western sky. At the moment of mid-totality (2:48 UT), the Moon will stand directly overhead from a point in the Atlantic Ocean a couple of hundred miles to the north of Belém, Brazil.
Upcoming Lunar Eclipses
There will be a partial eclipse of the Moon that will be visible across much of Europe and Asia on the night of Aug. 7, 2017. About 25-percent of the Moon’s diameter will become immersed in the umbra, leaving the upper three-quarters of the Moon visible. During the early morning hours of January 31, 2018, there be another total lunar eclipse; that one favors the western part of North America; eastern North America will see the Moon set during totality.
So although we’ve had a veritable plethora of total eclipses of late, keep in mind that after September 27, you’ll have to wait almost three years until your next chance to see another.
Check out our short video about the Full Harvest Moon and how it got its name.