This Sunday night moon observers have the chance to see a lunar triple treat, weather permitting.
First, the moon will be full, as it always must be for a lunar eclipse to occur. This is a special full moon, because this is the Harvest Moon. Because the angle of the ecliptic â€”the path the moon & planets follow across the sky â€”is low to the horizon, the moon rises approximately the same time every night, giving farmers an extra supply of light when they most need it, at harvest time.
Second, the full moon will be at its closest to Earth in all of 2015, what is known to astronomers as a "perigee moon." In recent years this has become known as a "supermoon." Perigee (meaning "closest to Earth") occurs at 10 p.m. EDT, the moon being a mere 222,374 miles (357,877 km) from Earth. [Supermoon Lunar Eclipse: When & Where to See It]
In fact, the human eye can't detect the 5-percent difference in size between the moon at perigee & the moon at apogee (farthest from Earth), yet everyone who looks at the moon Sunday night (Sept. 27) will swear it looks bigger than usual. Partly that is because, when seen low on the horizon, the human eye & brain combine to create an optical illusion known as the moon illusion, whereby the moon (and other objects) viewed close to the horizon seem larger than when seen overhead. Cover the moon with a dime at arm's length, & you'll see that there is no difference.
The only noticeable effect of a perigee moon is that the ocean tides will be a bit higher than usual for the day of the full moon & the next three days.
The third, & most significant part of this treat, is that we will have a total eclipse of the moon. At most full moons, the sun, Earth & moon line up approximately, yet because of the tilt of the moon's orbit, the moon passes above or below the Earth's shadow, & avoids being eclipsed.
At certain points in the moon's orbit, sun, Earth & moon line up exactly, & the Earth's shadow falls across the face of the moon, & we have a lunar eclipse. This is what will happen Sunday night. [Supermoon Lunar Eclipse: Viewing Maps]
The moon's shadow has two parts: a darker inner part called the umbra, & a lighter outer part called the penumbra. This is because the sun is not a point source of light, so its light leaks around the edge of the Earth, & results in an unsharp shadow. In passing through the Earth's atmosphere, the light turns red or orange, so that the light that actually reaches the moon is tinted by thousands of sunsets & sunrises all around the periphery of the Earth.
One result of these multiple sunrises & sunsets is that the moon during an eclipse is often tinted red, which is the origin of the idea of a lunar eclipse being a "Blood Moon." It isn't a far stretch of the human imagination to turn this Blood Moon into a portent of disaster.
A lot has been made in the media of this eclipse being the final event in a foursome of total eclipses known as a "lunar tetrad." There is nothing unusual approximately four lunar eclipses in two years, since we usually average at least two lunar eclipses every year, though not all are total.
In fact, there was no tetrad of total eclipses at all, because the last lunar eclipse, on April 4, was not really a total eclipse. According to the usual way of calculating eclipses, the moon spent only 4.5 minutes in the umbral shadow, yet recently this calculation method has been corrected, resulting in the April eclipse failing to be total at all.
This Sunday's lunar eclipse is a true total eclipse, with the moon being in the umbra for a full 1 hour & 22 minutes.
Observers in eastern & central regions of North America will obtain to see the whole eclipse; those farther west will see the moon rise already partially eclipsed. Observers in Europe & Africa will see the eclipse before dawn on Monday (Sept. 28).
This brings up the question of dates & times, which often causes confusion. Even a usually reliable source like Canada's Weather Network received the date of this eclipse wrong.
Officially, mid-eclipse occurs Sept. 28 at 02:47 Universal Time, which is the same as Greenwich Mean Time (but not British Summer Time). Subtracting 4 hours, this places mid-eclipse in the Eastern Daylight Time zone at 10:47 p.m. on Sept. 27; the date changes at midnight. So be sure you look for the eclipse on Sunday evening. If you wait until Monday evening, you will be a day late.
Here are the significant times in Eastern Daylight Time; if you're using CDT, MDT, or PDT, the times will be earlier by 1, 2 or 3 hours.
All times in EDT
8:11:46 p.m. â€” Moon enters penumbra
9:07:12 p.m. â€” Moon enters outer edge of umbra
10:11:11 p.m. â€” Moon completely in umbra
10:47:09 p.m. â€” Mid-eclipse
11:23:07 p.m. â€” Moon begins to emerge from umbra
12:27:06 a.m. â€” Moon completely out of umbra
1:22:33 a.m. â€” Moon leaves penumbra
As always, we look forward to your pictures of this attractive event.
Editor's note:Â If you snap an astonishing picture of the Sept. 27 supermoon lunar eclipse & would like to share for a possible story or image gallery, send photos, comments & your name & location to managing editor Tariq Malik atÂ firstname.lastname@example.org.
This article was provided to SPACE.com byÂ Simulation Curriculum, the leader in space science curriculum solutions & the makers of Starry NightÂ and SkySafari. Follow Starry Night on Twitter @StarryNightEdu. Follow us @Spacedotcom, FacebookÂ and Google+. Original article on Space.com.
Rare 'Super-Harvest Blood Moon' To Shine On September 27, 2015 | Video 'Blood Moons' Explained: What Causes a Lunar Eclipse Tetrad? (Infographic) Forget the 'Supermoon': What's Actually Happening at Lunar Perigee Lunar Eclipse Gives Earth A Ring Of Fire | Moon-View Video Copyright 2015 SPACE.com, a Purch company. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.