Harvest Supermoon Eclipse Result of Rare Combination of Celestial Events
Above, video by nature photographer Jerry Goldner shows Sunday's harvest supermoon eclipse over Chicago.
Weather permitting, the Chicago area will be treated to prime time, front-row seats for a rare astronomical phenomenon Sunday evening when a total lunar eclipse of a simultaneous harvest moon, supermoon and blood moon rises above the horizon.
Here's what will happen: The moon will move into the amber core of the Earth’s shadow at 8:07 p.m. and will proceed to darken and change color as the eclipse reaches totality between 9:11 p.m. and 10:23 p.m., according to the Adler Planetarium.
“The nice thing about this total lunar eclipse is that we don’t have to get here at midnight or three in the morning, or something like that,” said Adler Planetarium master educator Michelle Nichols. “The last three were late at night, early in the morning eclipses, as seen from Chicago. That’s why this one is so nice—it’s starting on a Sunday evening at 8:07 p.m., which is fantastic for us.”
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Sunday’s eclipse is the fourth and final total lunar eclipse in the current lunar tetrad of 2014-'15, bringing an extraordinary end to the series that began in April 2014. The eclipses of a tetrad are spaced apart by six lunar months. The last total lunar eclipse tetrad occurred in 2003-'04.
During the 21st century there will be a total of eight tetrads. If you miss it this weekend, prepare to wait: The next series begins in 17 years – that's April 2032. Over the course of the 20th century, there were only five visible tetrads. Prior to that, there was a 328-year drought from 1581 to 1909.
All the more reason to watch Sunday’s combination of events, which proves to be even more unusual.
“The last time that we had a supermoon perigee harvest moon lunar eclipse was Sept. 15, 1494,” Nichols explained. “This particular eclipse is interesting because it’s a total lunar eclipse and it’s a harvest moon—and it’s a supermoon. Supermoon just means that the moon is at perigee, meaning at that particular trip around the Earth, it is at its closest point to the Earth. Perigee happens once an orbit, it’s just that this time perigee coincides with the full moon phase.”
According to Nichols, the word "supermoon" is not an official astronomical term and was introduced in 1979 by astrologer Richard Nolle.
Another unofficial term associated with the event is the phrase "blood moon." When the full moon is eclipsed by the Earth, direct sunlight is blocked from the moon, but sunlight passes through the Earth’s atmosphere and continues to light the moon up, often resulting in a reddish or brownish color during totality. Despite hues that can range from brick red, copper and dark gray during a total lunar eclipse, the phrase blood moon stems from spiritual beliefs.
“Actually a blood moon has to do with people predicting doomsday prophecies, so it is not a scientific term,” Nichols said. “I think people have latched onto it because, yes, the moon can appear reddish during an eclipse and they think, oh, it’s reddish like blood. It has nothing to do with it and it’s not anything you’ll hear us using.”
The term that is astronomically sound is one we hear more frequently: harvest moon. What makes Sunday’s full moon fall into that category is the fact that it is occuring closest to the Northern Hemisphere’s autumn equinox and, due to the lower angle of the moon’s orbit around the Earth, the harvest moon will appear to look larger on the horizon.
“When the moon rises over the horizon, it comes up at a relatively shallow angle, so it appears near the horizon for a fairly long period of time,” Nichols said. “I guess that you could say if you were harvesting crops, and you needed the moonlight in order to do it, then the moon would be available to you on the horizon for a good period of time.”
Compared to a solar eclipse, a lunar eclipse is more common, lasts longer and, unlike a solar eclipse, a lunar eclipse can be viewed with the naked eye – there's no need for protective eyeware. Interestingly, there is a relationship between the two: a lunar eclipse occurs two weeks before or after a solar eclipse. This Sunday’s eclipse was preceded by a partial solar eclipse on Sept. 13.
Witnessing a total lunar eclipse can entirely depend on your location in the world. In some countries, Nichols explained, the eclipse might be partly finished by the time the moon rises or the moon might be setting during the eclipse, creating an inability to view the entire event.
“That’s what happened to us with the last total eclipse,” Nichols said. “The moon set before totality so we didn’t actually see totality here, we only saw the partial phase of the eclipse."
The Adler Planetarium will hold a “Lunar Eclipse Viewing Party” from 7-11:30 p.m. Sunday. Tickets are sold out, but Nichols said that the planetarium will allow those without tickets to set up telescopes on its grounds and even will provide a series of small telescopes manned by museum staff and volunteers, at no cost.
“Of any visible sky phenomenon like this, where you don’t need amazing telescopes or special equipment to see it and you can just walk out your door, look up, and there it is, the thing that I really like about the Adler is that people come down here expecting to view this, even though they know that they can see it from where they are,” Nichols said. “They want to be around other people who can either explain it, or people who are also geeking out about it, and they want to have that experience with a group of like-minded people who are also having the same experience. It will be fun."
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