The upcoming supermoon lunar eclipse explained

22 Sep 2015

Eclipses are events that everybody seems to enjoy, catching a few moments of utter darkness on seemingly rare occassions. But what is a supermoon? And how is it eclipsed?

Well, let’s start with the basics. Eclipses fall down two strands: solar eclipses and lunar eclipses.

The former is when the moon falls directly between the sun and Earth, hiding the sun from our view. It’s the eclipse that you are advised against staring at without protection over your eyes.

It’s also the eclipse that most people ignore advice over eye health, instead just looking up at a burning ball of fire and hoping for the best. These happen roughly twice every three years, depending what part of the world you live on.

Lunar eclipses are when Earth rests directly in between the sun and the moon, rendering the moon invisible as the reflective light with which we rely on to see it creeps away from view. There are around two a year of these, again geography dependent.

Supermoon lunar eclipse

A supermoon lunar eclipse, though, is entirely more rare. The moon’s orbit isn’t tied to a constant distance from Earth. Instead it’s on a bit of an oval circuit, coming close at points and moving further away again.

When the moon is farthest from Earth it’s called an apogee. When it is nearest to Earth it is called a perigee. At perigee the moon is more than the entire circumference of the planet closer to Earth, around 31,000 miles.

It looks about 14pc bigger to the naked eye, and is maybe double that in brightness. However, as we prefere hyperbole, we now call this a supermoon, leaving the more attractive name perigee to the astronomers.

A supermoon lunar eclipse is much rarer than the others, occuring only a handful of times in the past 100 years.

Indeed we haven’t seen one since the early 1980s, so people are understandably getting excited – the next occurance will be in 2033.

NASA has been out in force promoting the event, noting that the attraction is because entire generations will have never seen it happen.

Despite its rarity, NASA says the event is not cause for concern. “The only thing that will happen on Earth during an eclipse is that people will wake up the next morning with neck pain because they spent the night looking up,” said NASA’s Noah Petro.

The total eclipse will happen in the early hours of Monday morning (September 28), lasting for 70 minutes and visible to North and South America, Europe, Africa, and parts of west Asia and the eastern Pacific.

Viewers can see the supermoon unmasked after nightfall. Earth’s shadow will begin to dim the supermoon slightly, beginning at a little after 1am. A noticeable shadow will begin to fall on the moon at 2am, and the total eclipse will start at 3am.

Astronomy Ireland is hosting its own event for the occasion.

Main image and body image via Shutterstock

Gordon Hunt was a journalist with Silicon Republic