One Order Of Spring Please, Sunny Side Up

The sun rises over Lake Superior last week. Today marks the first day of spring when the sun rises due east and sets due west. Photo: Bob King

I celebrated the transition from winter to spring by taking a walk with my dog in the rain. We stepped out shortly after midnight this morning, me with umbrella in hand and Sammy nosing the ground. At 12:14 a.m. CDT at the stroke of spring I strained to listen for the first frogs. None were heard. They don’t usually begin calling until mid-April, but with temperatures in the 70s the past few days and snow vaporizing faster than a comet’s nucleus, my expectations were high.

Spring is when day and night are nearly equal across the entire planet. That’s because Earth’s axis is oriented neither toward nor away from the sun. If the southern hemisphere is the planet’s feet and northern hemisphere its head, today we’re 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 sun to pay for it. In summer, we’re tipped toward the sun with long days, a high sun and heat to spare.

The tip of Earth on its axis causes the seasons. On the first day of spring or vernal equinox, we face the sun from the side and days and nights are approximately of equal length in both northern and southern hemispheres. Credit: Tao-olunga

Spring and fall are the ‘tween times when temperatures moderate and the sun rests for a brief moment between extremes. And don’t forget the bonus alignment: at the equinoxes the sun rises due east and sets due west. If you’ve never been sure of your directions, this week is the time to get reacquainted. Face the sunset and stick out your arms. Your right arm points due north, your left south and your back faces east. Couldn’t be easier.

Where the sun is lower in the sky in the polar regions, its energy is more spread out and heats the ground and water much less than when it's high in the sky (b) and its rays are more concentrated. That's one of the reasons winter is so much colder than summer. Credit: Peter Halasz

Spring is that astronomical moment when the sun’s path crosses an imaginary circle in the sky called the celestial equator. The celestial version is an extension of the Earth’s equator into the sky. That’s why the sun is exactly overhead at the  real equator. An observant equatorian might notice that flagpoles or power poles cast no shadows at noon, because the poles literally stand right on top of them.

From here on out, the sun continues moving northward in the sky, which for those living in the northern hemisphere, means the sun gets higher and higher and daylight hours longer and longer until maxing out on June 20, the solstice. Not so for those living south of the equator, where the seasons run in exactly the opposite direction. It’s the autumnal equinox down under. The sun’s headed lower in the sky, bringing with it shorter days and longer nights.

A low sun at the North Pole photographed on April 8, 2008. The temperature at the time was 14 below F. Click image to webcam page. Credit: NOAA/North Pole webcam

The sun’s apparent movement north or south in the sky is a result of the Earth’s axial tilt of 23.5 degrees, which in turn is amount the Sun moves north or south of the equator during a year.

If you’re trekking to the North Pole today, situated at latitude 90 degrees north, the sun will make its first appearance of the year on your horizon at local noon … and it won’t set for the next six months! It doesn’t matter what direction you look either since it’s up all night and day.

At 90 degrees north, the celestial equator rings the horizon. Not until the sun reaches this point – which happens on the first day of spring – does it finally return for observers at the pole. Conversely, today is the last day the sun is up for the next six months for an observer at the South Pole. I hope your spirits rise today like the sun in the new season. Happy equinox!

Before and after pictures of supernova 2012 aw in M95. The image at left was taken in April 2008 before the explosion; the other just a few days ago. Credit: William Wiethoff

The new supernova in M95 in Leo, shining at magnitude 13.1, now has a name – 2012 aw. It doesn’t sound like much but if you add an “e” you’ve got an eyeful of “awe”.

10 Responses

  1. Pam

    Couple questions on Spring Equinox phenomenon of standing eggs up on end.

    We have been doing that since we were kids. I noticed it does not work on the Fall equinox.

    Does that mean it is reversed for the Southern & Northern Hemispheres like the seasons? So that the southern hemisphere can only balance the eggs on the September Equinox?

    Also, I’m curious to know the physics of why it works with the eggs if anyone happens to know that – is it because of the yolk inside the white substance, etc. I know if the eggs are too cold it doesn’t work, or if you get an egg that is not wider on the bottom. Also sometimes you have a bad egg, 2 yolks. Does it matter if the yolk is broken on the inside?


    1. astrobob

      Hi Pam,
      There’s actually no connection between the equinoxes and eggs standing on end – just a widely-repeated rumor that’s been going around for years. The egg is symbolic of fertility and growth and came to be associated with spring.

  2. thomas s

    hi Bob, just an interesting aside. we have an east facing sitting room. so when we have our morning coffee, we can watch the sunrise “move” from SE in Dec to due east in Mar and NE in June (and back again). it’s a nice astronomy lesson. besides it’s free.

  3. Steve

    Hi Bob,
    I was wondering if it is possible for sunspot 1429 to continue its life all the way around for a second rotation. I’ve noticed it’s still kicking out cme’s.

      1. Steve

        Would it be given a new sunspot number, or would it still be named 1429? Also, I LOVE your blog! Could you maybe write on the topic of astrophotography for the beginner?

        1. astrobob

          Hi Steve,
          It will be renamed should it reappear. Some groups can reappear several times; each time they’re assigned new numbers. Tell me what kind of astrophotography you’re interested in – star trails, through the scope, etc. and I’ll see what I can do. I’ve done a couple blogs on the topic that you may not have seen. Thank you for your kind words about the blog.

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