From CNN:
One of the brightest heralds of spring makes its appearance this week.
The March full moon, known as the worm moon, will be at its peak at 3:18 a.m. ET on Friday, March 18, according to NASA. It will appear full through Saturday morning.
(See more below for, er, how it got its name.)
This moon will appear larger to viewers because of the “moon illusion,” according to the Old Farmer’s Almanac. This occurs when the moon is near the horizon and our eyes compare the moon’s size to trees, buildings or other earthly objects. By comparing these reference points to the moon, our brain tricks us into thinking the moon is bigger.
Southern Native American tribes named the worm moon after the earthworm casts — essentially feces — that emerged as the ground thawed at winter’s end, according to NASA.