By Michelle Durham

PHILADELPHIA (CBS) – When you look up into the sky tonight, you might see a lot more moon than you’re used to. An area expert calls it an optical illusion.

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Chief Astronomer at the Franklin Institute Derrick Pitts explains the Supermoon.

“The supermoon is a phenomenon that occurs when the full moon phase coincides with a perigee of the moon. Perigee is when the moon makes its close approach to the earth as it does monthly.”

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Pitts says the moon will appear larger then usual, but he says this happens every month when it rises in full phase.

“When we see the full moon rising near objects of known size, our brain plays a trick on us in which it makes the moon appear larger then it actually is.”

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It is true the moon affects the tides, but Pitts doesn’t expect any danger or significant tidal issues. And as far as this moon being bad luck in terms of triggering earthquakes or volcanic activity, Pitts says that is just superstition.