Once in a blue moon
The moon rose just shy of full on New Year’s Eve, promising a supermoon early in 2018. On January 2, the moon rose as a perigree full moon, when its orbit is closest to Earth, so it looks larger and brighter. The moon experiences perigree once per orbit, but that doesn’t always coincide with a full moon. On average, the distance from the center of the moon to the center of Earth is 238,000 miles. The moon will wane and wax to a blue moon on January 31, called ‘blue’ because it is the second full moon in one month, a once-every-2.5 years occurrence. Because the lunar cycle is 29.5 days, there will be no full moon in February, which happens only about four times a century.