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It’s the Equinox! Do you Know Where your Sun is?

March 20th is the vernal equinox here in the northern hemisphere and the autumnal equinox in the southern hemisphere. During the equinox, the sun crosses the plane of the equator, making night and day approximately equal in length.

Why is the equinox important for permaculture?

One of the first questions my PDC instructor posed to us was, “where does the sun rise?" Well everyone knows the answer to that; the sun rises in the east. No brainer. Alas, we were wrong. Unless you live at the equator, the sun does not rise directly in the east. In the northern hemisphere, it rises in the southeast (or in the northeast if you’re in the southern hemisphere). Nor is the sun at 90° overhead at noon. Depending on the season, here in Phoenix, Arizona (latitude 33° N), the sun can be at an angle ranging from 32° on the winter solstice, to 78° on the summer solstice. These are critical distinctions when designing your site plan.

The equinox is one of the three times of year when it’s beneficial to observe the location of the sun at sunrise, noon and sunset and note the effect of the sun’s angle and shadows on your property. Summer solstice, when the sun is at its highest in the sky, and the winter solstice, when it is lowest in the sky, are the other two times when sun angles should be noted. Either the vernal or autumnal equinox will give you a good ‘middle ground’ observation as a comparison to these two extremes.


Sun angle in the northern hemisphere on the summer solstice,
vernal/autumnal equinox and winter solstice.

The sun’s angle at various times of the year will influence placement of a number of key features in your site plan. These might include: where you place the windows of a structure, how big those windows are, what kind of roof overhang you need to shade those windows, where to place solar panels, where to locate trees, shrubs and trellises, where to put a vegetable garden and more. The angle of the sun, along with correctly placed architectural and landscape features, work together to passively heat or cool your home.


Sun angle and a deciduous tree work together to passively cool and heat a home

Sun angle and climate: one woman’s “learning experience”

Here at Dolce Verde, my 1/6 acre, urban permaculture site in downtown Phoenix, Arizona, I spend a good deal of time trying to escape the harsh desert sun and its accompanying heat.

Phoenix starts to heat up around the vernal equinox and starts to cool off again around the autumnal equinox. This year (2013), we got a bit of a head start on the heat by setting a record of 94° F (34° C) on March 14. Oh yeah. Summer’s on its way, baby! In Phoenix this means at least 100 days of over 100° F temperatures, with 25+ of those days above 110° F (43° C).

So with shade and sun angle in mind, I provide you with one example of how observations made during the equinox have led to improvements in one of my early permaculture projects – my first veggie garden.

The first garden I ever installed at Dolce Verde was in the NE corner. My property has a wall around it, so this NE corner made a wonderful, warm garden in winter because the “L” shape of the walls retained the southern and western sun and reflected light and heat back into the garden.


The NE veggie garden ‘before’

But remember, we’re in Phoenix. By mid-March (the equinox), that particular garden starts to heat up and my winter crops start to bolt prematurely. By now, I’m sure you can see the problem with my garden placement. This corner becomes a solar oven starting in mid-March and lasts through the end of September. Had I taken the time to observe my property a little longer before digging, I may have opted for a different placement.

But in permaculture we work with what we’ve got, and my small property does not have unlimited options for garden placement. So with subsequent observation of sun angles, I’ve managed to mitigate some of the “solar oven” effect over time.

To cut down on reflected light and heat, I’ve planted an evergreen citrus hedge along the walls, which drops the temperature a couple of degrees. The hedge has not yet covered all the wall space so I expect to see further gains in cooling as the hedge fills in. I also planted two deciduous trees that provide overhead shade for the garden in the summer. The addition of shade cloth helps extend the life of warm weather crops until I let the garden go fallow in August. And while this corner is still hot, it’s definitely not as hot as it used to be!


The NE veggie garden ‘evolving’

So, if you have a little time on March 20th this year, dust off your site plan or grab your camera, and record the sun and shadows cast by the features of your property in the morning, midday and evening. If you keep these over the years, you’ll have a great visual of how your property has evolved to take advantage of, or protect you from, the angle of the sun. And you never know when those measurements might provide the solution to a problem!

I’d love to hear other people’s stories about how they’ve used sun angle observations to solve a problem.

9 Comments

  1. I found this article very helpful in preparing plans for my soon-to-be purchased land here in Texas. As a Phoenix born native, I couldn’t help but remember the heat given off by our block fence. Your use of citrus as a heat sink is a brilliant stacking idea given how much citrus love the heat!

  2. Hi Randy:

    Thanks for the kind words.

    Block fences do seem to intensify our already stifling heat and they are so prolific here. However, as you say, the citrus trees don’t seem to mind the reflected heat/light at all. And when we had a heavy freeze here in Feb, those same citrus trees suffered only minor damage as they were protected in their cozy microclimate.

    Best of luck to you on your new property and hoping to see posts about what you do with that land.

    Jennifer

  3. Hi Jennifer

    Useful article to remind people to think seasonally, especially in the temperate zones.

    I was struck by the comment that the Sun does not rise directly in the East. It does on the equinox’s! No matter where you are on earth :) I am in Hamilton in New Zealand, the Sun rises 30 degrees south of East (true East) on the Summer solstice and 30 degrees north of East on the Winter solstice (21st June), a swing of 60 degrees in compass bearing thru the year. This gets wider with higher latitude and tighter near the equator. No matter where you live on earth you will always get a 46 degree change in elevation of the Sun thru the year. The Sun may not always be above the horizon of course (beyond 66.5 degrees north or south) even at the equator the Sun will still swing thru 46 degrees, 23 either side of directly over head. Today the Sun will rise directly East in Phoenix and set directly West, just as it will down here.

    This site has a really useful diagram to show both bearing and elevation for any place on earth
    https://www.gaisma.com/en/dir/001-continent.html

    cheers

  4. Thanks guys!

    I have my camera charging as I type this, along with a list of items I want to photograph so I can take the same shots/angles on the solstices. Then I’ll save the list so I can repeat these same shots in coming years.

    I wish I’d had this methodology from the beginning, but enthusiam prevailed over long term logic!

  5. Peter – that is so interesting. I always assumed it was slightly off of “true east” (not necessarily observable by eye), even on the equinox, unless you lived at the equator. Thanks for the cool link!

  6. Very intersting cousin. Yes, that’s right, cousin. Never saw this kind of garden planning. Pretty cool, or hot, or in between. Sorry, couldn’t resist.

  7. Hey Brett:

    Nice to see you on here. Don’t know if you have a garden in Florida but this method works well there too (hint).

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