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Equal Night: The Vernal Equinox

March 20, 2012

image credit: wiki.naturalfrequency.com Today is the vernal equinox for those of us in the northern hemisphere; the autumnal equinox for those in the southern hemisphere. The equinox is the twice-yearly event in the earth’s orbit around the sun when the sun’s rays reach all parts of the globe  equally. The word “equinox” is from the Latin roots “equi” and “nox” meaning “equal night.” The equinox has “equal night” in two senses. First the length of the night (and the day) is about equal all over the globe on this date. Second, the hours of light and hours of dark are approximately equal, at about 12 hours each.

The table below shows sunrise and sunset times today for a selection of locations around the world. As you can see, the length of day (and night) for every one of these places is close to 12 hours. I was surprised to discover, however, that none of these locations had exactly equal hours of day and night (12 hours each) on the equinox. Instead, places in the northern hemisphere had their 12-hour day and 12-hour night 2-5 days (depending on location) before the equinox, and those in the southern hemisphere will have their 12-hour day and 12-hour night 2-5 days after the equinox.

Location Sunrise Sunset Length of day
Poland, Maine (US) 6:45 6:53 12:8
Gettysburg, Pennsylvania (US) 7:12 7:21 12:9
Naples, Florida (US) 7:31 7:38 12:7
Seattle, Washington (US) 7:12 7:21 12:9
Los Angeles, California (US) 6:57 7:04 12:7
Kotzebue, Alaska (US) 8:50 9:05 12:15
Whitehorse, Yukon (Canada) 8:02 8:14 12:12
Toronto, Ontario (Canada) 7:21 7:29 12:8
London, England 6:03 6:13 12:10
Oslo, Norway 6:18 6:31 12:12
Kuala Lumpur, Malaysia 7:17 7:24 12:7
Mumbai, India 6:43 6:50 12:7
Cairo, Egypt 5:59 6:06 12:7
Cape Town, South Africa 6:50 6:58 12:8
Melbourne, Australia 7:23 7:32 12:9
Christchurch, New Zealand 7:32 7:42 12:10
Lima, Peru 6:12 6:19 12:7
Buenos Aires, Argentina 6:57 7:05 12:9
McMordo Station, Antarctica 7:43 8:18 12:35

 

For those who garden near the equator, days and nights are close to equal all the time, and the equinox is not a major event. But the further away from the equator we travel, the greater the difference in length of day as we move from solstice to equinox to solstice. For many who garden in northern latitudes, the vernal equinox marks the psychological beginning of the garden season. Even if we still have snow in our gardens or the still-thawing ground is much too soggy to work, this is the point in the year when hours of daylight become longer than hours of darkness. From now until the summer solstice, as our part of the earth tilts toward the sun, the days will just keep getting longer and longer and the temperatures milder and milder. Plants will spring up and bloom, and the barren garden scene of winter will turn lush and green.

Let the gardening begin!

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26 Comments leave one →
  1. March 20, 2012 11:40 am

    YEAH! Spring is here! I just love the longer hours of daylight, because it means more time for gardening.

    • March 24, 2012 11:29 am

      Lucy, I agree. I am now able to go out and check on the garden before I leave for work in the morning and also have it light when I get home at the end of the day. I love that!

  2. March 20, 2012 1:19 pm

    Jean – how well you pulled this together. I’m not good at this sort of subject but you’ve cast new light on time and the world for me. Suddenly I feel more connnected – here we are all with roughly the same number of hours of daylight! Feel a bit foolish but no, I never knew that!

    • March 24, 2012 11:34 am

      Jane, I will confess that I don’t entirely grasp the way that the earth’s tilt on its axis creates different patterns of light and dark as the earth orbits around the sun. I have some rudimentary understanding of the basics, but I’m not very good at imagining two-dimensional diagrams like the one I’ve included here in 3 dimensions. Someday I should go to one of those three-dimensional demonstrations with a bright lamp to represent the sun at the center and a model earth orbiting around it in the appropriate elliptical pattern and with the right tilt to the axis so that you can actually see the different patterns of light and dark in the northern and southern hemispheres at different points in the orbit.

  3. Elephant's Eye permalink
    March 20, 2012 3:00 pm

    the barren is turning green – it is weird to see a tough plant that was bravely hanging in there, suddenly overnight producing bunches of leaves, and flowers. Just waiting hopefully for some soaking rain.

    • March 24, 2012 11:38 am

      Diana, Because I’ve spent most of my life living in places where seasonal change was dependent primarily on temperature, I forget that in many parts of the world the important seasons are wet and dry. I never totally got used to this during the two years after college when I lived in southern California. I was totally amazed the first year when the rains came in November and the brown hills suddenly turned green; I was equally amazed by how quickly they turned back to brown after the rains stopped in March.

  4. March 20, 2012 3:26 pm

    and we’re off aren’t we.we have the hottest March on record ever and the heat is not being enjoyed by early bulbs..many bloom and are gone in a day or 2…but my veg garden is planted with cool season veggies and the garden is still a soggy mess…oh well I will get there…Happy Spring!! I actually was jumping for joy and breathing in the fresh spring air this morning!! Feels like May already my fav month…

    • March 24, 2012 11:42 am

      Donna, It does feel like May; it got up to 80F here yesterday. Unfortunately, May weather is associated in my students’ brains (well, to tell the truth, in mine, too!) with the end of the school year — but we are at mid-semester and the heaviest work is still ahead of us. I always dread hot weather early in spring because it means I’m going to have to drag students (whose brains have already switched over to summer mode) through the rest of the semester by sheer force of will.

  5. March 20, 2012 3:37 pm

    Just imagine; here in Denmark the days are now nearly 5 hours longer than they were in December… And when we reach the Summer solstice our days will be another 5 hours longer, and the night will technically be twilight, as the sun never moves very far below the horizon.

    It is a wonderful time of year!

    • March 24, 2012 11:48 am

      Soren, I associate all that light with joy, and I just feel light and joyful at this time of year. Even in Maine, the US doesn’t get as dramatic an increase in length of day as you do in Denmark. In my part of Maine, we gain a little over 3 hours from winter solstice to equinox and another 3+ hours from equinox to summer solstice. Some year, I’ll get to your part of the world in early summer and just revel in all that light.

      • March 25, 2012 2:41 am

        Light is life, isn’t it? And even though this is still just spring – and unreliably so – we can at least enjoy that longer days herald summer in all it’s coming glory. (And I won’t think of last year’s miserably wet and cold summer…)

  6. Nell Jean permalink
    March 20, 2012 5:03 pm

    It makes my head bizzy to contemplate all the differenent gardening practices related to distance from the equator and the sun.

  7. Nell Jean permalink
    March 20, 2012 5:06 pm

    Differenent? The finger to click is quicker than the eye.

    • March 24, 2012 11:51 am

      Nell, The funny thing is that my eye had trouble finding the spelling error even after you pointed it out; the human brain is very good at smoothing things out and making them “right.” But all those different climates and practices are amazing (and getting to connect with them is one of the things I love about garden blogging). Vive la differenence! :-)

  8. March 20, 2012 8:05 pm

    I’ve heard of the equinox before but I must admit I didn’t actually know what it was. Certainly noticing though the increasing day length here. I was actually able to walk about the garden this evening after coming home from work. One of my delights in summer.

    • March 24, 2012 1:23 pm

      Marguerite, I’m also now getting home in the light and finding it delightful.

  9. March 21, 2012 8:13 am

    It’s good, because it means longer days, but it’s bad, because it means it’s time to panic over jobs not yet completed.

    • March 24, 2012 1:24 pm

      IG, I’m guessing this panic is more an issue for those growing veggies than for gardeners like me who are mostly growing perennial flowering plants. The perennials are much more forgiving about when you put them in the ground.

  10. March 21, 2012 8:36 am

    Well, I didn’t know this. I’ve heard the term “equinox” since a child, and it was just one of those things which sounded too scientific for me to bother wondering about. It’s actually very simple…

    • March 24, 2012 1:26 pm

      Bobby, Thanks for visiting! It warms my teacherly heart to think that I made something that seemed too complex to bother about simple and understandable. :-)

  11. March 21, 2012 7:50 pm

    So interesting, Jean. And it is nice to know where many are during this time period. The temperatures have been mild for some time. Now, I wonder if we will have a long spring or a short spring. I am hoping for the former…

    • March 24, 2012 1:27 pm

      Michelle, After the much-higher-than-average temperatures of recent weeks, spring seems to be happening at high velocity in Gettysburg.

  12. March 23, 2012 12:21 pm

    I agree, let the gardening begin! This always feel like such an optimistic time of year, lots of promise, both of longer and warmer days, and garden bounty. Happy Spring!

    • March 24, 2012 1:29 pm

      Clare, You’re right; it is an optimistic time of year. For me, the longer days and warmer temperatures signal that the end of school is coming, and part of my optimism is anticipation of the time and relaxation that will be coming my way in a few weeks.

  13. March 24, 2012 7:59 am

    Thanks for allowing me to focus on what the equinox means—I had forgotten. I celebrate the date when days become longer, but I am more excited about the day when day light savings ends. Always amazes me how much more daylight we have in PA than ME.

    • March 24, 2012 1:36 pm

      Carolyn, I was fascinated by your perception that there is more daylight in PA than in Maine — because Maine has about 30 minutes more daylight in June, while PA has about 30 minutes more daylight in December. I wonder if your perception is a result of the fact that Pennsylvania is about 30 minutes further west in the time zone so there is more light in the afternoon. On the summer solstice, for example, Portland Maine will have a longer day than Philadelphia, but sunset in Philadelphia will happen about 5 minutes later (while sunrise in Portland will come more than 30 minutes earlier). I think most people experience light at the end of the day as more light. I’m just the opposite; because I’m a morning person, I like my light early in the day. One of the things I find most difficult about coming back to PA for the beginning of school each semester is the 30-minute later sunrise; I hate getting up in the dark, and I absolutely loathe having to walk to work in the dark.

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