The next Supermoon of 2019 arrives tonight with a full moon appearing a bit larger and brighter than it usually does throughout the year. Making this event more rare is when it occurs: at the same time as the spring equinox. Not since 2000 did a supermoon coincide with the first day of spring; this isn’t expected to happen again until 2030. Tonight’s Supermoon is also known as the “Worm Moon” because it coincides with the time of year when earthworms begin to emerge from the thawing soils across the Northern Hemisphere.
The Supermoon technically arrived at 3:45pm ET yesterday, but the main act arrives this evening at 9:43pm ET. Yesterday, the Moon reached perigee, with only 223,309 miles between the Earth and the Moon. Tonight, the moon reaches full phase, delighting sky watchers with a brilliant full Moon that should appear a bit larger than normal. As a result of this timing, tonight’s full moon should appear 14 percent larger and 12 percent brighter than usual.
“The supermoons are a great opportunity for people to start looking at the Moon, not just that once but every chance they have!” says Noah Petro, a research scientist from NASA’s Goddard Space Flight Center.
Apogee and Perigee
The moon’s orbit around Earth is far from a perfect circle. The 27 day voyage of Earth’s satellite is actually an elliptical orbit with an ever changing distance. The casual observer will notice the phases of the moon as it makes this orbit but the more subtle change, and also noticeable, is the slight change in distance as well. During the course of any given month the distance between the Earth and the moon will vary by close to 30,000 miles. The farthest point is called apogee, the moon being a distant 252,712 miles from Earth. Perigee is the closest point with that distance shrinking to 221,519 miles. A full moon at perigee will appear a bit larger and much brighter than a full moon at apogee.
This Year’s Supermoon
This supermoon is the last one for 2019.
The supermoon classification is a term that was coined by astrologer Richard Nolle in 1979. Nolle used the supermoon term to describe a new or full moon that occurs when the moon is in the top 10% of it’s closest distance to Earth. There was never a reason given why the 10% value was chosen and the term “supermoon” is not recognized in the astronomical community, but has certainly taken hold with the general population and media reports. Given that every 27 days there is a full and new moon along with perigee and apogee point the supermoon is not that uncommon.
There will also be some unwanted effects of the full moon/perigee combination. The ebb and flow of the tides is a direct result of the moon’s gravitational pull on the Earth’s waters. During a new and full moon this force is not competing with the Sun’s smaller gravitational pull and can lead to higher than normal tides. These tides occur typically twice a month and are never really noticed by anyone. This gravitational force however can change and is directly related to the distance between two objects, shorten that distance and that force will increase. So when you have a regular tide along with a supermoon then you may be in for minor flooding on or near each high tide.
The best time to really appreciate the supermoon will be as the moon is close the the horizon and will appear larger due to the moon illusion phenomenon.
See how one photographer captures the moon in stunning pictures around New York City here: Photographer Wows with NYC Imagery