equinox Archives - The Spacewriter's Ramblings

Today, March 19, 2020, is the March equinox. Calendrically speaking, it’s the first day of spring in the northern hemisphere and the first day of autumn in the southern hemisphere. So, happy new season, wherever you are hunkering down during the world-wide pandemic of COVID-19. If you can, step outside for some fresh air and wave to your neighbors (distantly) and enjoy the new season!

The Equinox, Solstice, and our Calendar

Solstices and equinoxes are calendar dates actually related to astronomy and the motions of our planet. Most people think of them as the “start” of a season. They aren’t weather predictions, but are related to positions of the Sun as seen from Earth’s surface. It appears to move, but it’s actually a result of Earth spinning on its axis.

Think of a merry-go-round. If you’re on it and look out at people standing around watching it spin they appear to move. But, they’re really standing still. It’s YOU (and the merry-go-round) that is moving.

It’s the same with Earth. As the planet spins around on its axis, we see the Sun appear to rise in the east and set in the west. Same thing with the Moon and stars. They look like they’re moving across the sky. That apparent motion is at the heart of why we calculate equinox and solstice dates. (Solstices happen in December and June.)

Understanding the Solstice and Equinox

Watch the sunrise and sunset each day (and remember: don’t directly at the Sun). If you do this for a while, you’ll notice that its rise and set points change throughout the year. The Sun also seems to move farther north or farther south through the year. Its sunrise, sunset, and zenith points slide slowly to the north from December 21-22 to June 20-21 each year. After that, they almost stop (or stand still) before stopping. Then, the Sun appears to pause for a day or two before starting the slow daily slide toward the south. That southward trip goes from June 20-21st (the northernmost point) to December 21-22 (the southernmost point).

Solstice sunset in the Rockies. An equinox sunset would be due west. — A winter sunset, where the Sun is very far south along the horizon. On the equinox, the sunset occurs due west. Copyright Carolyn Collins Petersen

Those “stopping points” are called the “solstices” (from the Latin word sol, which means “sun”, and sistere, which means “stand still”). These terms are a heritage from our ancient ancestors. They had an incomplete understanding of Earth’s motions in space but did notice that the Sun appeared to stand still at its northernmost and southernmost points, before resuming its apparent motion south and north (respectively).

Solstice Facts

The summer solstice is the longest day of the year for each hemisphere. For northern hemisphere observers, the June solstice (the 20th or 21st), marks the beginning of summer. In the southern hemisphere, that’s the shortest day of the year and marks the beginning of winter.

Then, six months go by. On December 21st or 22nd, winter begins with the shortest day of the year for the northern hemisphere people. The lucky folks south of the equator get to enjoy the start of summer the same day, with the longest day of their year.

Equinoxes

The word “equinox” also has Latin roots. It comes from aequus (equal) and nox (night). Early observers noticed that the Sun rises and sets exactly due east and due west on the equinoxes. It also appears to cross the celestial equator, a projection of Earth’s equator out to the sky. In addition, day and night are approximately the same lengths.

A shot from the International Space Station of the setting Sun on the June equinox in 2008. Courtesy NASA.

In the northern hemisphere, the March equinox denotes spring and autumn in the southern hemisphere. The September equinox is the first day of fall in the north and the first day of spring in the south.

So, the solstices and equinoxes are important calendar points that come to us from the apparent position of the Sun in our sky. They are also intimately connected to the seasons but are not the sole reason why we have seasons.

Observing the Solstices and Equinoxes

While you can’t “see” the equinox or solstice actually happen, you can chart the motions of the Sun to see how it was that the ancients first came up with these ideas. Take a moment each day to observe the sky. Make a note of where sunset or sunrise takes place along the horizon. Check out your chart against the calendar to see how close they line up.

This is actually a great long-term science activity and I know that it’s a perennial favorite for science fairs. A couple of years ago, I actually went out each night at sunset and got a picture of the sunset using my smartphone. That’s certainly an easy way to do it, and lets you document how the Sun appears to wander north and south along the western horizon.

When Day and Night are Equal Length

The equinox terminator satellite view. Courtesy miss_braceys photostream at http://www.flickr.com/photos/30086332@N06/

The equinox terminator GOES satellite view. Click to embiggen. Courtesy miss_bracey's photostream at http://www.flickr.com/photos/30086332@N06/

On this auspicious occasion I’d like to wish you a happy March Equinox. It’s an astronomically derived “holiday” of sorts, and what it means is that the Sun’s apparent path in the sky throughout the year crosses from the southern celestial hemisphere into the northern one.

People often think of this as the first day of spring (for northern hemisphere dwellers) or the first day of autumn (for folks south of the equator), although as Phil Plait points out, that’s not quite correct. (Read here for why he says that.)

People also often — and wrongly — say that this is the only time that you can do something you wouldn’t normally do: balance an egg on its end. I ran into this bit of conventional weirdness (the opposite of conventional wisdom) back when I worked at a newspaper. I came in to work one day in early March (well before the equinox) and all the copy desk editors were engrossed in a conversation about how you could balance an egg on its end only on the equinox. I asked them that could be and they didn’t know, but thought it make a cool “weird science” story. I told them it was weird, but it wasn’t science, and that set off another discussion that ended with me buying a dozen eggs and bringing them back up to the office and showing them that you could balance them on any day, not just the equinox or the first day of autumn or any other conveniently interesting date.

Imagine if you will the messy desks of a newsroom, each one with an egg balanced on it. And NOT on the equinox. and a bunch of smart-aleck copy desk editors scratching their heads because what they thought they knew was wrong. Another beautiful theory bit the dust as reality proved it wrong.

Phil Plait (his BadAstronomy-ness himself) made a great movie showing how the egg thing works throughout the year. Check it out here.

Living With a Star

Equinoxes and solstices are some of the things we live with because we live near a star. So are the seasons. And so is space weather. Speaking of which, in all the excitement yesterday, I forgot to post an entry here directing you to 365 Days of Astronomy (which you should be listening to every day anyway, right?). I had an entry about space weather, so go check it out.

Are They Really That Ignorant?

Speaking of the change of seasons and calendrical things, there’s a fascinating bit of data out there about how only 53% of adults in the U.S. in a survey conducted by the California Academy of Sciences know how long it takes for the Earth to go once around the Sun. That’s pretty bad. What’s even worse is that nearly 40% of those same people thought that humans and dinosaurs lived at the same time. That IS also something that the earliest humans knew as they trod the plains of Africa only 160,000 or so years ago. The earliest primate ancestors of humans didn’t even exist when dinosaurs did. That’s because dinosaurs were thriving some 65 MILLION years ago (before a combination of factors, including a killer asteroid of some kind, started them down the road to extinction). At that time, only the most primitive mammal ancestors of humans existed. (There’s a nice explanation of when primates did show up at this site.) Nary a human nor primate of any kind was to be found. The first hominid (a form of primate that was the immediate predecessor to us) didn’t show up until about 4.4 million years ago. That’s a LONG time after the dinosaurs bit the dust. And, there’s fossil evidence aplenty to prove it. Hard, cold data.

But, that doesn’t stop some folks from making up faux science out of whole cloth (and some kind of curious shame over evolution) to make money on dinosaur-human theories. And, apparently it doesn’t stop others from believing what these charlatans say instead of checking it out for themselves. The whole thing kind of begs the question about the quality of science education these people got. If they got any.

Anyway, see how you stack up against the rest of the folks who took the test — surf on over to CalAcademy (link above) and take their mini quiz on science — it comprises six questions on their front page. I did, and I only got one wrong (and it wasn’t the one about the year or the dinosaurs). See if you can beat my score!

The Spacewriter's Ramblings

Category Archives: equinox

The Equinox is Upon Us!