Spring Equinox
Winter Solstice
December's winter solstice occurs when the sun reaches its southernmost point in the sky. With it, comes the shortest day of the year and the longest night in the northern hemisphere. It also marks the beginning of winter. This year, the winter solstice begins 11:23 a.m. Eastern time on December 21.
Summer Solstice
In contrast, the summer solstice in June marks the longest day of the year in the northern hemisphere, when the sun reaches its highest point in the sky. It's also the beginning of summer. The next summer solstice will be June 21, 2019.
New Moon
More frequent than the equinoxes or solstices are the different phases of the moon, and they're easily observable for most people in the world, no matter how much light pollution, air pollution or cloud cover they live with. A new moon is the first lunar phase, and it is the one time none of the moon is visible. This happens when the moon and sun have the same ecliptic longitude, meaning the sun and Earth sit exactly opposite sides of the moon. Since the moon doesn't radiate its own light (what we see of the moon is light from the sun), none of the moon is visible to the naked eye.
Full Moon
In contrast to a new moon, a full moon is fully visible. This occurs when the Earth is between the sun and the moon, and everything is lined up perfectly. A full moon is the third of four lunar phases, the other being new, first quarter and third-quarter moon phases.
Harvest Moon
A harvest moon is the first full moon that is closest to the fall equinox. This year, North Americans can see one on September 24.
Supermoon
A supermoon is also a full moon. But it occurs when a full moon coincides with the moon's closest approach to Earth. The effects of a supermoon are said to be difficult to spot with the naked eye, though the moon will appear 30 percent brighter and 14 percent larger when it meets the supermoon criteria.
