The Wolf Moon is the full moon which occurs in January. Thus, it is the first moon of early winter.

Native Americans belonging to the Algonquin tribes of the eastern United States and Canada named the Wolf Moon for the hungry wolves which often turned up outside native villages at this time of winter. The wolves would start lurking around the villages around this time of year because their easiest prey had already been caught earlier in the winter, while other prey animals had migrated south or gone into hibernation. By January, the wolf pack was starting to suffer from the shortage of prey. Usually wolves avoid human presence, but hungry wolves start looking for an opportunity.

The Wolf Moon is one of the brightest of all the full moons of the year. This is due to its reflection off the snow and its position in the sky.

Reflectiveness is measured as albedo, with 1.0 being perfect reflection of all light. Although the moon’s albedo is only 0.136, the albedo of freshly-fallen snow can be as high as 0.9. As a result, the reflection of the full moon’s light off the snow is very bright.

Because the full moon is always opposite the sun, the full moon always rises highest in the sky during winter. A full moon in winter is as high in the sky as the sun is in summer.

Some Wolf Moons, such as the full moon of January 2010, are also brighter because they are closer to the earth. Because the moon’s orbit is an ellipse, the nearest part of its orbit is about 31,000 miles closer to the earth than the farthest part. As a result, the moon’s apparent size in the sky also changes. When the moon is at perigee, the closest point, it can look up to 14% larger and 30% brighter than at the far end of its orbit.

Tides are also higher during perigee. A full moon tide is already an unusually high tide, so a full moon tide which coincides with the perigee is a very high tide. Nor’easters may also bring an additional storm surge during winter.

However, the perigee is not connected with the phase of the moon. In fact, the orbital period of the moon is 27.32 days long, more than 2 days shorter than the lunar month, which is 29.53 days long. As a result, most Wolf Moons do not occur when the moon is at its perigee.

In England, the Wolf Moon is also known as the Old Moon or the Moon After Yule. Some Algonquin tribes called it the Snow Moon instead, but most Algonquin tribes saved that name for the next month’s full moon, when the heaviest snows fall and food is scarce. In some tribes, the Snow Moon was also known as the Hunger Moon.