equinox – Watch the Skies

March Equinox Welcomes ‘Astronomical’ Spring

by Lance D. Davis

Did you know our planet has two types of seasons? They are meteorological and astronomical. What’s the difference?

“Meteorological seasons” follow the changing of the calendar, month to month, and are based on the annual temperature cycle – seasonal temperature variations modified by fluctuations in the amount of solar radiation received by Earth’s surface over the course of a year. For instance, the meteorological season of spring begins each year on March 1 and will end on May 31.

However, “astronomical” seasons happen because of the tilt of Earth’s axis (with respect to the Sun-Earth plane), and our planet’s position during its orbit around the Sun.

An illustration of the March (spring) and September (fall or autumn) equinoxes. During the equinoxes, both hemispheres receive nearly equal amounts of daylight. (Image not to scale) Credits: NASA/GSFC/Genna Duberstein

The March equinox – also called the vernal equinox – is the astronomical beginning of the spring season in the Northern Hemisphere. Seasons are reversed in the Southern Hemisphere where it will be autumn, also known as fall. These simultaneous seasons will occur March 20, 2022, at 15:33 UTC (Coordinated Universal Time) or 10:33 a.m. CDT (Central Daylight Time).

Equinox Solstice Info Graphic — Click to view larger. Credit: NASA/Space Place

The Sun will pass directly above the equator, bringing nearly equal amounts of day and night on all parts of Earth. At the equator, an equinox results in about 12 hours of daylight and 12 hours of night.

Equinoxes and solstices are caused by Earth’s tilt on its axis and the ceaseless motion it has while orbiting the Sun. Think of them like events happening as our planet make its journey around the Sun.

North of the equator, the March equinox will also bring us earlier sunrises, later sunsets, softer winds, and budding plants. With the reversed season, those south of the equator will experience later sunrises, earlier sunsets, chillier winds, and dry, falling leaves.

If you’re in the Northern Hemisphere, watch the Sun as it sets just a bit farther north on the horizon each evening until the June solstice – when the Sun reverses directions, moving back to the south. Also, get outside to enjoy the warmer weather and extended daylight!

Happy March equinox, Earthlings!

March Equinox Brings 2 Seasons: Spring, Autumn

The March equinox – also called the vernal equinox – is the beginning of the spring season in the Northern Hemisphere and autumn season in the Southern Hemisphere. It arrives on March 20, 2021, at 09:37 UTC (Coordinated Universal Time) or 4:37 a.m. CDT (Central Daylight Time).

An illustration of the March (spring) and September (fall or autumn) equinoxes. During the equinoxes, both hemispheres receive equal amounts of daylight. Credit: NASA/JPL-Caltech

During this equinox, the Sun will shine directly on the equator with nearly equal amounts of day and night, about 12 hours. Throughout the world, the Northern and Southern hemispheres will get equal amounts of daylight.

Click to view larger. Credit: NASA/Space Place

The equinoxes and solstices are caused by Earth’s tilt on its axis and ceaseless motion in orbit. Think of an equinox as happening on the imaginary dome of our sky, or as an event that happens in Earth’s orbit around the Sun.

In the Northern Hemisphere, the March equinox will bring us earlier sunrises, later sunsets, softer winds, and budding plants. With the opposite season, south of the equator, there will be later sunrises, earlier sunsets, chillier winds, and dry, falling leaves.

If you’re in the Northern Hemisphere, start watching the Sun as it sets just a bit farther north on the horizon each evening until the summer solstice. Also, enjoy the warmer weather and extended daylight!

The Autumnal Equinox is Near

Happy equinox, Earthlings! Sept. 22 marks the fall equinox, when day and night are nearly equal.

“However, that day/night length depends on where you are on Earth,” said NASA solar scientist Mitzi Adams. “For example, at the North and South Poles, the length of the day and night is six months!”

At the North Pole, the Sun will sink below the horizon for a kind of twilight from now until sometime in October when it will be completely dark, explained Adams. Spring twilight begins a few weeks before the vernal, or spring, equinox in March, when the Sun rises above the horizon again.

Autumnal Equinox — Credit: NASA/JPL-Caltech

This only happens twice in Earth’s year-long trip around the Sun. The rest of the year, the Sun shines unevenly over the Northern and Southern Hemispheres. That’s because Earth’s axis is tilted with respect to the Sun-Earth plane. But on these special days – the spring and fall equinox – the Sun shines equally on both north and south.

Here in the Northern Hemisphere, it’s the first day of astronomical fall. From now until the beginning of spring, nighttime hours will last longer than daylight as the Sun travels a shorter arc across the sky each day. The Sun has its shortest path of the year at the time of the winter solstice — the shortest day and longest night of the year — when sunrise and sunset are as far south as they can go (at any one location). It’s just the opposite in the Southern Hemisphere, where September 22 kicks off astronomical spring.

The equinox—meaning “equal night” in Latin—occurs at 8:31 a.m. CDT.

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.) (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. (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)