The full harvest supermoon will shine brightly in the night sky Tuesday evening. A partial lunar eclipse, with a “bite” taken from the moon, will also be visible.

Not only is September's full moon also a so-called "supermoon" because of its size and brightness, but it's also due to be eclipsed by Earth.

If you happened to notice the supermoon looking especially large as it was rising, you may have fallen victim to a “well-known, poorly studied optical illusion,” said NASA’s Noah Petro. Here’s the scientific explanation of what you were seeing,