... Since moonshine is really reflected sunlight, the full Moon is on the average slightly brighter in mid-winter, when Earth is closest to the Sun. In addition, the distance of the full Moon also varies, due to the ellipticity ("eccentricity") of the Moon's orbit. On 22 December, 1999, the two effects combined to produce the brightest full Moon of the century. ... This year will be the first full moon to occur on the winter solstice, Dec. 22nd, commonly called the first day of winter. ...