After shoveling another 8 inches of snow after a winter of white, the banks along my walkway are now nearly at eye level. If there’s a lawn under there, I’m gonna need a team of archaeologists to find it. No matter, that won’t stop spring.
Tomorrow morning at 6:02 a.m. (Central time) the sun quietly slips over the line into the northern half of the sky. We call this the vernal equinox or start of spring. For me it will be a matter of faith in the cyclical movement of the sun. For you, the zephyrs of the new season may already be blowing through your hair.
On the first day of spring, Earth’s axis is oriented neither toward nor away from the sun. If the southern hemisphere represents the planet’s feet and northern hemisphere its head, tomorrow we’ll be showing the sun our belly or profile if you like. In winter, the northern hemisphere is tipped away from the sun with short days and a low, chilly sun. In summer, we’re tipped toward the sun with long days, a high sun and more heat than most of us need. But during the vernal and autumnal equinoxes, neither hemisphere has the solar advantage (or disadvantage) and equality rules. Days are 12 hours long, nights are 12 hours long.
The sun also also rises due east and sets due west. If you’ve ever been puzzled by which direction is which in your neighborhood, face the sunset sun around the time of the equinoxes and stick out both your arms at your sides. Your right arm points due north, the left due south. Pretty handy, eh?
Spring and fall are the in-between times when temperatures moderate and the sun rests for a brief moment between extremes. For folks living on the equator, tomorrow the sun will rise in the east and pass directly overhead at noon before declining in the west. Equatorial skywatchers will stand in their own shadows at local noon.
Take an imaginary flight to Earth’s south pole and tomorrow means something quite different. There the sun will hover along the horizon 24 hours straight, neither rising nor setting. Starting March 21, it won’t breach the horizon for another 6 months. What marks the start of spring for northerners means the beginning of fall for Australians and a temporary end of sunshine for itinerant Antarcticans.
As you’d expect, the situation is just the opposite at the north pole, where 6 months of daylight begins with tomorrow’s sunrise.
Our planet’s tilted axis combined with its yearly orbit makes such strange things happen here on the ground. Just think how monotonous the weather and daylight-length would be if our axis were straight up and down with no tilt. Our skewed planet is like an artist looking at the world from varied and surprising perspectives.
Spring also coincides with a series of fine morning passes of the International Space Station (ISS) for at least the U.S. and Canada. Less than an hour before spring’s start, the station will pass over northern Minnesota tomorrow morning. To find times when it’s visible from your location, log on to Heavens Above (which also provides excellent maps of its path in the sky) or key in your zip code at Spaceweather Satellite Flybys page. The ISS first appears in the western sky and moves eastward, appearing like a very bright, moving star.
Space Station times for Duluth, Minn. region:
* Tues. March 20 starting at 5:14 a.m. “Magically” appears out of Earth’s shadow high in the southern sky and moves east. Brilliant pass!
* Weds. March 21 at 5:58 p.m. across the northern sky
* Thurs. March 22 at 5:09 a.m. Exits Earth’s shadow at 5:09 a.m. above the North Star and moves eastward
* Fri. March 23 at 5:52 a.m. across the northern sky
* Sat. March 24 at 5:03 a.m. Exits Earth’s shadow just below the North Star and moves east
* Sun. March 25 at 5:46 a.m. across the northern sky