By Lauren Casey

PHILADELPHIA (CBS) –– On Monday, we have the opportunity to witness an astronomical sight that last occurred 68 years ago. This month’s full moon will not only be ‘super’, but ‘mega-super’, and it all has to do with the shape of the moon’s orbit around the Earth.

Derrick Pitts, Chief Astronomer and Planetarium Director for the Franklin Institute explains, ‘the moon’s orbit is not a circle, but it is an ellipse, that means it has points to when the moon is closer to Earth or farther away from Earth in it’s orbit, and those points are called apogee and perigee. In this case we’re talking about a lunar perigee when the moon is closer to Earth than normal during the course of the month.’

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At perigee, the moon is on average about 30,000 miles closer to Earth than at apogee, but can vary to a degree in that closeness. And according to Mr. Pitts, ‘it happens that this year, it will be the closest of those perigees that has happened since 1948.’ As a result, Monday’s Supermoon will appear up to 14-percent bigger and 30 percent brighter than other full moons.

And to view an enhanced ‘super’ effect, look to when the moon is near the horizon, either when rising or setting. Pitts states that ‘when the moon is down close to the horizon near objects of known size, our brain plays a trick on us, and it makes us think that the moon is much bigger than it actually is, it just looks that way.’

An optical illusion called ‘moon illusion’. Another ‘trick’ of science that yields a treat for the eyes, is when the moon takes on a reddish hue, an effect which results as moonlight passes through our near-surface atmosphere, which is the thickest portion.

As Mr. Pitts describes, ‘all the other colors are scattered around so you can’t see them, but you do see this coppery, reddish color instead, so as the moon rises it’s moving into thinner sections of the atmosphere, as you look through, so you no longer see those colors anymore and the moon looks almost white.’

Moonrise is at 5:20 pm on Monday evening. And when you’re out moon-gazing, Derrick Pitts suggests looking toward the southwestern sky to catch a view of both the planet Venus, which will appear as a very bright star, and the planet Mars which will have a rosey glow.