March Equinox

An Image of the Earth during the March Equinox

Credit: NASA

Spring Has Sprung: The Equinox And The Reason For The Season

March 19, 2017

Nevermind the snow on the ground. As of Monday morning at 6:20am, it's officially spring.

Sure. You might say spring really begins when, say, the trees begin to bud or when you finally start your garden, but it's arrival actually has less to do with what is happening down here on the ground and more to do with what's happening up in the sky; in particular, the equinox.

"Equinox is from a Latin word aequinoctium which means equal nights," explained Kelly Beatty, Senior Editor for Sky + Telescope Magazine.

Equal nights and equal days. On the equinox, there are essentially 12 hours of sunlight and 12 hours of darkness, everywhere on the planet. And for us in the Northern Hemisphere, the March equinox kicks off a 6-month period where our days are longer than our nights.

In fact, that we have spring — or any season for that matter — is thanks to our yearly trip around the sun and a lucky little tilt.

"We go through these seasons because the Earth's axis, it's spin axis, is tipped over about 23 degrees from upright," Beatty explained. 

Despite the fact that Earth is actually closest to the sun in January, for us in the northern hemisphere, we are tilted toward the sun during the spring and summer, and away from it in the fall and winter.

"That causes the sunlight to both be more intense and it's in the sky longer during the course of the day and so that's why we have [spring and] summer," Beatty said. 

The warming evenings of spring are the perfect time to get outside and do some stargazing, according to Beatty. And, so what is there to see up there in the skies this season? In a word: Planets.

Computer generated global image of Venus
Photo Credit: Image credit: NASA/JPL

Mercury Rising, Venus Sinking 
In the early evening darkness, just after sunset, if you look to the west just above the horizon, you'll see a very bright star that is not really a star at all, but the planet Venus. Beatty says spotting it is a "no-brainer."

"It's so much brighter, it's very easy to see," he said.

Once you identify Venus, Beatty says look to its left by about the width of a fist where a much dimmer Mercury is also visible.

Over the next few weeks, night by night, Mercury will rise higher in the sky, and Venus will sink lower.

"Watch it night by night, become an official stargazer," suggested Beatty.

Cassini portrait of Jupiter
Photo Credit: NASA/JPL/Space Science Institute

Gas Giant To The East 
In the eastern skies this spring, Beatty says the gas giant Jupiter is also waiting to be viewed.

"Jupiter just passed what astronomers call opposition," said Beatty. "What this means is that [this season] Jupiter is as close to us as it's going to get and it will be up in the sky all night."

Beatty says with a small telescope, or even a good pair of binoculars, you'll be able to see not only that Jupiter is indeed a disc rather than simply a bright dot, but also four tiny "pinpricks" of light around it, which are Jupiter's four brightest moons. 

And a pro tip from Beatty: If you are going to try to take a look through binoculars, make sure you steady them. 

"Just lean up against a wall or a tree," he said. "It's really easy to do."

Saturn's Rings imaged by Cassini
Photo Credit: NASA/JPL-Caltech/Space Science Institute

A Ringer In The Skies 
For you early morning risers, there’s one more planetary treat for you this season, visible to the south in the hours just before sunrise: Saturn.

Saturn, like Earth, is also tilted and, right now, Beatty says the tip is such that Saturn's famous rings are wide open to us.

It'll take a small telescope to see those rings, but Beatty says if you can get your hands on one, it's well worth it.

"For a lot of us stargazers, we got our start, we got hooked, when we first saw Saturn through a telescope," he said. "It's just surreal to see with your eye. It's just breathtakingly beautiful."

Now I’m sure you’re plenty busy this spring, but why not take just a moment, look up, and note the reason for the seasons — that perpetual cosmic dance?

"Planet comes from the ancient Greek word "to wander," and so they wander among the stars." said Beatty. "It's just pretty, and it's interesting to watch them move around."

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