Werewolves and Moon lovers get ready. Tonight’s plenilune will be the brightest we are going to get this year, as July's full moon will be a so-called Supermoon, which happens when the near side of the Moon is not just fully illuminated but our natural satellite is at the closest point in its orbit to us.
Because the Moon’s orbit, while being very close to a circle, is actually an ellipse, there are times that it is closer to Earth – which is called the perigee – and other times where it is further away – called the apogee. The average distance between the Earth and the Moon is 384,400 kilometers (238,900 miles).
When a full moon happens when the Moon is in perigee, our satellite tends to appear slightly bigger and a fair bit brighter than when it is at the apogee, around a 14 percent increase in size and 30 percent increase in brightness, according to NASA.
This difference has earned it the nickname "Supermoon". The opposite is a "micromoon" but the difference is small enough that you wouldn't notice if you didn’t know it’s happening.
Given that there is no astronomical definition for this regular occurrence, there is no strict distinction that marks it. Astrophysicist Fred Espenak defined it as a full Moon that occurs when the Moon is within 90 percent of its closest approach to Earth. Based on that you get three or four per year, all in a row.
Of the four happening in 2022, from May to August, tonight’s one will be the closest to the perigee. If you want to properly see one as close to the perigee as possible you’ll have to wait until December 6, 2022. The next best one is on November 25, 2034.
You may even see the optical trick called the Moon illusion. This happens when the Moon is low on the horizon giving the impression that it is massive and much closer than normal.
Moonrise is expected at 9 pm EST, and you have all night to watch it. If the weather is not playing ball where you are, worry not. The Virtual Telescope Project has you covered. Their team will be streaming the plenilune from 2 pm EST in the video below: