Remember all the supermoons last summer? The astronomical event of this evening will be a phenomenon sometimes called a "black supermoon," and it's the cause of a coastal flood advisory for the Bay Area until Thursday. The takeaway: the moon will basically disappear and the stars will be out and about. What does it mean? Your horoscopes in the comments.
For lunar novices, a supermoon is the coincidence of a full moon or a new moon (in this case, a new moon) with the closest approach it makes to Earth on its elliptical orbit. It's also called a "perigee moon." The moon, which is usually about 238,000 miles from Earth, will tonight be approximately 12,000 miles closer to our planet.
Of course we won't be able to see the supermoon's occurrence during the day, and since it's a new moon, we won't see it at night, either. In fact, it'll get out of the way almost completely, making for —as Universe Today puts it — "a prime time to go deep for faint objects while the light polluting Moon is safely out of the sky." So go on a starlit hike, because the black supermoon won’t be back — or seemingly gone — until October, 2016.
Down on Earth, though, the proximity of the moon will have a serious effect on tides. Per the previously mentioned advisory, "The sun... moon... and earth are in proper alignment to bring the largest tidal cycle of the season which will occur over the next few days. These excessive tides are often referred to as King Tides or Perigean Spring Tides and will result in minor coastal flooding of low-lying areas along the coast and bay fronts during periods of high tide."
This guy, for example, was a recent victim of these extra high tides around the Bay.