September’s Harvest Moon will also play host to yet another lunar phenomena, a total lunar eclipse.
2015 has been a great year for lunar activity. This single year contains a blue moon, six super-moons and two total lunar eclipses, the second of which will occur on September 27th (September 28th Universal Time). We had the first total eclipse on April 4th.
What is a lunar eclipse? There are two varieties. The first is an umbral or total lunar eclipse. This occurs when the Moon passes directly into the darkest part of the shadow left by the Earth passing in front of the Sun. A penumbral or partial lunar eclipse is far less dramatic. The penumbra is a more diffuse shadow caused when the Sun is not completely occulted by Earth. The type of eclipse experienced is simply a matter of chance due to slight variations in our orbits year to year.
So, why does the Moon turn red? Well, the big reason is that Earth, which is blocking the Sun, has an atmosphere that refracts light much farther out than the disk of our planet. The atmosphere traps a lot of the shorter, blue wavelengths of light, allowing the longer, red wavelengths to pass through. Much like our setting sun bathes the world around us in deep warm hues, that same concept permits the Moon to be cast in an even deeper shade of red-orange, but only after the Moon enters the umbra.
Each eclipse is unique and based on the Moon’s position it may appear to go through less or more of the Earth’s shadow, yielding darkness of varying duration. The progress of an eclipse is tracked by noting the various points of contact as measured from the limb or edge of the Moon’s disk. See below for a description of each point of contact in reference to either the leading of trailing edge of the Moon, known as limbs.
- P1 = Leading edge contacts the Penumbral shadow
- P2 = Trailing edge contacts the Penumbral shadow
- U1= Leading edge contacts the Umbra
- U2 = Trailing edge contacts the Umbra
- U3 = Leading edge starts to emerge from Umbra
- U4 = Moon has completely left the Umbra
- P3 = Leading edge starts to emerge from Penumbra
- P4 = Moon has completely left Penumbra
The September 27th eclipse will start before sunset in much of the U.S. Only the eastern U.S. should be able to view P1, although this is not generally discernable to the naked eye. U1 marks the point that is more traditionally viewed as the beginning of the eclipse. Please see the contact point chart below for precise times for each event. Totality will last 1 hour, 11 minutes, although the umbral shadow on the Moon’s surface should be visible for more than 3 hours.
If you choose to attempt to photograph the eclipse, you’ll need a sturdy tripod, a long telephoto lens and a remote shutter release to avoid camera shake. The built in self timer can be used if a remote shutter release in unavailable. The Moon is often captured at low ISO and high shutter speeds, as it is a very bright object. However, not surprisingly the Moon is much darker during totality. Even at a relatively high ISO, the shutter speed is much slower during this period and you may need an astronomical mount with some tracking ability to attain sharp images. It’s best to get out an experiment with your equipment several days in advance of the event. This will be your last opportunity for some time, as no total lunar eclipses are predicted for 2016.
Even if you don’t choose to photograph the eclipse, just sitting back in a lawn chair on a cool evening is a heck of way to bid farewell to Summer and welcome Autumn.
Contact Point Times
|Hours||Offset from UTC||-4||-5||-6||-7|
|P1||12:11:47 AM||8:11:47 PM||7:11:47 PM||6:11:47 PM||5:11:47 PM|
|U1||1:07:11 AM||9:07:11 PM||8:07:11 PM||7:07:11 PM||6:07:11 PM|
|U2||2:11:10 AM||10:11:10 PM||9:11:10 PM||8:11:10 PM||7:11:10 PM|
|U3||3:23:05 AM||11:23:05 PM||10:23:05 PM||9:23:05 PM||8:23:05 PM|
|U4||4:27:03 AM||12:27:03 AM||11:27:03 PM||10:27:03 PM||9:27:03 PM|
|P4||5:22:27 AM||1:22:27 AM||12:22:27 AM||11:22:27 PM||10:22:27 PM|