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.