After another long winter, we could all use a little spring. Yes, winter sports are great, but many of us are ready to turn the page. It’s time for spring 2023 to begin, at least astronomically, and it will arrive tomorrow afternoon, March 20, at 4:24 PM CDT, the exact time of the spring equinox.
In 2007, Congress changed the start of daylight saving time to the second Sunday in March. Before 2007, it started in April. The earlier start gives us, in a way, a preview of spring. Of course, the beginning of daylight saving time is more visible than the spring equinox because of the dramatic increase in daylight in the early evening, even though the weather outside may be cooler than spring.
However, the vernal equinox is a big deal astronomically because the Sun crosses the celestial equator moving further north and higher in our sky. Earth revolves around the sun with its axis tilted 23.5 degrees from its orbit around our home star. Because of this, the sun’s path through the star background, known as the ecliptic, is inclined to the celestial equator by the same 23.5 degrees. The celestial equator is merely a projection onto our sky of the Earth’s terrestrial equator and occupies the same mathematical plane. Around the Twin Cities and vicinity, the celestial equator is an imaginary line that stretches from the eastern to the western horizon. Its highest point is to the south, halfway from the horizon to the zenith overhead.
At 4:24 Monday afternoon, the sun will appear on the celestial equator in our sky. On the day of the spring equinox in March and the autumnal equinox in September, the sun shines directly over the Earth’s equator. At noon, anywhere along the equator, the sun will be directly overhead. The northern and southern hemispheres experience equal amounts of sunlight.
At the summer solstice in late June, when the sun’s most direct rays shine over Earth’s northern hemisphere, the sun reaches its highest point in our sky at midday. The sun is at its maximum distance north of the celestial equator, so daylight hours are maximum and nights are shortest. At the winter solstice in late December, the sun’s most direct rays shine over Earth’s southern hemisphere, which puts the sun very low in our sky at its maximum separation south of the celestial equator. The days are the shortest and the nights are the longest.
Almost without fail, on the day of the vernal equinox, you’ll see either a TV weatherman or an anchor trying to balance an egg on its side. If the end rises, they will claim it is due to the vernal equinox. The truth is that the vernal equinox has nothing to do with it. Your chance of getting an egg to stand is no better or worse than any other day of the year!
No doubt you have been told that the days and nights are equal in length at the vernal and autumnal equinoxes. Everyone around the world experiences 12 hours of daylight and twelve hours of night. Guess what? This is still a myth! Indeed, it is true that both hemispheres receive equal sunlight, but the days are already longer than the nights. Just check the almanac data in the Pioneer Press and you’ll see we’ll have 12 hours and 9 minutes of daylight today. The days and nights were equal last Friday, March 17th, St. Patrick’s Day!
The Earth’s atmosphere is responsible for this. Sunlight coming from 93 million miles away is bent by the envelope of Earth’s atmosphere, something called astronomical refraction. The thicker the atmosphere, the more curved the sunlight. Whenever the sun rises or sets at any time of the year, its light must pass through much more of our atmosphere than when it shines high in the sky. The bending of sunlight is so extreme at the horizon that the sun’s disk will appear above the horizon when it is actually below it, giving us extra natural light.
Until about 1750, England and early America did not celebrate the New Year on January 1st. The New Year was celebrated on the same day as the vernal equinox. That’s because on the first day of spring, the plants and trees slowly start to turn green and nature begins again. Champagne corks popped as flowers bloomed. After this winter prison, believe me, I want to open some champagne too!
England and the colonies still operated under an ancient calendar with roots dating back to Babylonian times. Most of the Western world, especially Roman Catholic countries, switched to the Gregorian calendar in the late 1500s. That calendar had January 1 as the first day of the year. In reality, it was a correction of the Julian calendar going back to 46 BC, which also had January 1 as the start of the New Year. England finally decided in 1750 that it was time to synchronize with the rest of the Western world and adopted the Gregorian calendar.
Happy spring and happy birthday!
Celestial Happening this week: The new crescent moon will pass the bright planets Jupiter and Venus later this week. Wednesday evening in twilight, about 40 minutes after sunset, look for a very thin crescent just above Jupiter, very low in the western sky, just above the horizon. Early Thursday evening, a slightly thicker crescent will be just below the very bright planet Venus in the western sky. Friday evening, the moon will be above Venus. With binoculars or a small telescope, you see, you can spot the faint and very distant planet Uranus, just off the lower left edge of the Moon. It will look like a faint blue-green star. Uranus is just under 1.9 billion miles from Earth this week!
Mike Lynch is an amateur astronomer and retired broadcast meteorologist for WCCO Radio in Minneapolis/St. Paul. He is the author of “Stars: a Month by Month Tour of the Constellations,” published by Adventure Publications and available at bookstores and adventurepublications.net. Mike is available for private celebrity parties. You can contact him at firstname.lastname@example.org.