There is an eclipse Sunday evening and after so many days of clear skies and mild temperatures, itís going to be a tough break if clouds disrupt us from seeing it. As of right now, there should be enough clear spots in the sky to see the eclipse quite well. Iíll be updating weather conditions on Twitter @growingwisdom. I put the details of the eclipse later in this entry. Letís discuss the supermoon thing first.
Although words like ďsuper moonĒ and ďrareĒ are used in eye catching headlines. These terms arenít what astronomical professionals will use to describe this event. While these phenomena donít happen all the time, they have happened before and will certainly again. The length of time between these types of lunar eclipses warrants calling it rare. I enjoy teaching about astronomical events, and while meteorologists arenít astronomers the cool occurrences in the sky often fall to us to explain.
Roughly every 30 days there is a full moon. The moon is full when the Sun, Earth and moon line up and the Earth in the middle. When we look up, the moon is fully illuminated. During this time, because the moon is exactly opposite the sun in the sky, the moon rises in the east just as the sun sets in the west. Then, roughly 12 hours later, the moon sets in the west just as the sun is rising in the east.
These three bodies are continuously revolving around each one another, the moon about the Earth and the Earth about the sun. This means although we hear about a full moon occurring on a particular day, itís really an instantaneous event, occurring when the moon is exactly opposite the sun. This week, such an alignment happens 10:50 p.m. EDT (02:50 GMT) on Sunday September 28th.
Like the sun, the moon is not always the same distance from the Earth. In the relationship between the Earth and the Sun, the two are furthest around July 4th each year and this is called perihelion, the two bodies are closest around January 3rd and this is called aphelion. It's counter-intuitive because it's cold in winter when the Sun and Earth are at their shortest distance from each other.
Near and Far
The moon will be closest to the earth on Sunday, just two weeks after being at itís furthest point from the Earth. You can see from the chart below that each month there is a perigee and apogee with the moon, unlike the relationship with the Sun. Whatís happening this weekend of the 13 close approaches the moon makes to the Earth this year, this one is the closest. Since the Earth-moon distance is shorter, the moon will appear bigger, thus the term ďsupermoonĒ. While the moon might appear bigger and brighter, the difference isnít really all that much.
Sundayís moon is the closest encounter with Earth until November 14, 2016. The full moon on November 14, 2016, will be the closest full moon (356,509 kilometers) until November 25, 2034 (356,448 kilometers). So yes, these things are interesting, but not all that uncommon.
Not So Super
In a recent article in the Evening Sun, Ian Clarke, director of the Hatter Planetarium at Gettysburg College told the newspaper the following, ďTake a quarter and hold it 103 inches away from you. That's the apparent size of the moon relative to us, as we see it. Take that same quarter, and bring it 5 inches closer, 98 inches away from you. That's the effect of the Supermoon, he said.Ē As you can see, this isnít the celestial event of the century.
Whatís happening Sunday evening is an eclipse of the moon, in its full state, while making its closest approach of the year. The eclipse begin at 8:11 p.m. ET. The moon will be fully covered at at 10:11 p.m. ET, peaking at 10:47 p.m. ET. The moon stays covered until 11:23 p.m.ET, and the eclipse will end at 12:27 a.m ET
You only need to look towards the east to watch this event. There arenít any special glasses or special precautions to take. However, if you are driving, pay attention to the road, not the moon. During the time the Earth gets in the way of the Sunís light from illuminating the moon, the moon will take on a reddish hue. This is why you are hearing the term ďblood moonĒ associated with this eclipse.
The image below, courtesy of Sky and Telescope does a great job of explaining the upcoming eclipse.
There have only been five supermoon eclipses since 1900 (in 1910, 1928, 1946, 1964 and 1982). After Sunday, the next supermoon eclipse will occur in 2033. There will however be other lunar eclipses. Even better, August 21st 2017, a full solar eclipse visible across most of the United States.