The December 2025 Full Moon will occur on Thursday, December 4, beginning with a moonrise over Florida's east coast at 5:08 p.m. Eastern Standard Time (with a few minutes of variation depending on your exact location). This is the last full moon of the year and also a Supermoon. The Full Moon will technically be 100% full at 6:14 p.m. Eastern Standard Time on December 4, according to the U.S. Naval Observatory. What is a Supermoon? According to NASA, a Supermoon occurs because the Moon is in an elliptical orbit around the Earth. When the Moon is closest, it is at its orbital perigee, which is why a Super Moon is also known as a Perigee Moon. At its closest point, the full moon can appear up to 14 percent bigger and 30 percent brighter than the faintest Moon of the year, which occurs when it’s farthest from Earth in its orbit. A full moon at its closest point to Earth definitely will be big and bright. But it won’t look much, if any, different than a “normal” full moon and will not have any readily observable effect on our planet except perhaps slightly higher tides for most areas around the world and much higher King Tides in South Florida. Why is December’s Full Moon Called a Full Cold Moon or Long Night’s Moon? According to the Farmer’s Almanac, December’s Full Moon has the seasonal names of “Full Cold Moon,” “Long Night’s Moon” and the “Moon Before Yule.” December’s full moon is often the closest full moon to the longest night of the year on the Winter Solstice. December Full Moon and the Number 12 The number 12 is significant to the moon because there are 12 months in a calendar year based on roughly 12 full moons occurring in the year. For math nerds, the number 12 is considered a sublime number, one “that has a perfect number of divisors, and the sum of its divisors is also a perfect number.” Perhaps that is why ancient mathematicians chose an “hour” to represent 1/12th of the day and 1/12th of the night and 12 inches in a foot. Full Moon High Tide For those planning to walk, bike, or run along the beach in Florida, this Full Moon brings along with it a 3.5 ft. + Atlantic Ocean high tide on the east coast and a 2.5 ft. + high tide on Florida's Gulf Coast.