Tonight, Wednesday February 18, the moon will be closer to Earth than at any other time during its orbit around our planet. When this happens, astronomers call it perigee, and although perigee takes place once every month, it only sometimes coincides with a full or new moon. But when it does, this gives rise to a supermoon, like the one that will be in the night sky tonight. Because the moon is so close — about 13,000 miles closer than average — supermoons can be a spectacular site, shining up to 30% brighter and appearing 14% larger in the sky than other full moons. That’s because tonight there will be a new moon — when the moon is between the Earth and the sun, shown in the diagram below. At that location in space, the moon lies in the sun’s shadow, so we do not see it light up in the night sky.
What makes tonight’s supermoon different than others is that it is also a black moon. Chances are, you’ve heard the term blue moon in reference to a rare event in the saying “once in a blue moon”. In some respect, a black moon, while rare, is the exact opposite of a blue moon. A blue moon refers either to the second full moon in a single month or the third full moon in a single season, such as summer and winter. A black moon follows the same rules as a blue moon, except instead of being full, the moon is in its first phase called “new” for a black moon. The black moon happening this Wednesday is the third new moon during the winter season and it is taking place on the same day that the moon is closest to Earth. Hence the term ‘black supermoon’. So, if you were hoping for a supermoon like the one in June 2013 in the image below, you’re out of luck this time around. But you don’t have long to wait for the next full supermoon to take place.
There are six supermoons happening this year. The next one will take place on March 20th and will, again, coincide with a new moon and also a solar eclipse. (Although, only viewers in Europe, nothern Africa, and parts of Asia will have see the eclipse.) The last three will happen during a full moon and take place in August, September, and October. On September 28, the supermoon will occur around the same time as a total lunar eclipse, where the east coast will have prime seating for the event.
The black moon tonight can look very dark so, keep an eye out for the thin crescent sliver that shines through before or after the event.