A fall harvest supermoon put on a rare celestial show Tuesday when it also created a partial lunar eclipse for skygazers around the world. The bright harvest supermoon — a full moon that happens around the autumnal equinox — entered Earth’s shadow around 10:13 p.

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.

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,