Here Comes the Sun… and Moon!

Happy equinox, Earthlings! March 20 marks the spring equinox, one of two seasonal markers in Earth’s year-long orbit when the Sun appears to shine directly over the equator, and daytime and nighttime are nearly equal lengths–12 hours–everywhere on the planet.

During the equinoxes, both hemispheres receive equal amounts of daylight. (Image not to scale.)
During the equinoxes, both hemispheres receive equal amounts of daylight. (Image not to scale.) (NASA/GSFC/Genna Duberstein)

It’s the start of astronomical spring in the Northern Hemisphere, meaning more sunlight and longer days. From here until the beginning of fall, daytime will be longer than nighttime as the Sun travels a longer, higher arc across the sky each day, reaching a peak at the start of summer. It’s just the opposite in the Southern Hemisphere, where March 20 marks the fall equinox.

What’s more? The first full Moon of spring will rise tonight, lighting the skies on the equinox. Usually, a full Moon arrives a few days to weeks before or after the equinox. It’s close, but not a perfect match. Tonight’s full Moon, however, reaches maximum illumination less than four hours after the equinox. There hasn’t been a comparable coincidence since the spring equinox in 2000.

When the Moon, on its orbit around Earth, reaches the point farthest from the Sun, we see a full Moon.
When the Moon, on its orbit around Earth, reaches the point farthest from the Sun, we see a full Moon. (NASA/GSFC/Genna Duberstein)

And because the Moon is near perigee, it qualifies as a supermoon–the third and final of 2019. It’s not a big supermoon, so you won’t really be able to see the difference between this full Moon and any other one with your eyes. But keep an keep an eye on the Moon as it rises and creeps above the eastern skyline. A low-hanging Moon can appear strangely inflated. This is the Moon illusion at work.

Super or seemingly not, it’s a rare celestial coincidence to usher in springtime.

Look For The Harvest Moon This Weekend

Take a moment to gaze at the beautiful harvest moon this Saturday, September 29th.

(Image credit: NASA)

The harvest moon gets its name from agriculture. In the days before electric lights, farmers depended on bright moonlight to extend the workday beyond sunset. It was the only way they could gather their ripening crops in time for market. The full moon closest to the autumnal equinox became “the harvest moon,” and it was always a welcome sight.

Northern summer changed to fall last Saturday, Sept. 22nd, and is called the autumnal equinox. The word equinox comes from the Latin words for “equal night.” The fall and spring equinoxes are the only days of the year in which the Sun crosses the celestial equator.

Keep an eye on the moon as it creeps above the eastern skyline. The golden sphere may appear inflated. This is the moon illusion at work. This optical illusion is caused by the moon’s proximity to distant objects. A harvest moon inflated by the moon illusion is simply beautiful to us, but even more so to the farmers getting their crops in on those cool autumn evenings.

(Image credit: Stefano De Rosa)