astralsled
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Joined: Wed Dec 31, 2014 8:56 am
Location: Pittsburgh, PA

Calculating or predicting sunlight levels for summer?

I have been container gardening vegetables, greens, and fruit with moderate success for a few years now, but just moved to a house with a yard and am excited to start planting in the ground! However, I'm unsure how much sun to plan for. My yard is southeast facing, but in this season is unfortunately mostly shade except in the early morning. The yard is surrounded by a fence and bordered on the west side by the next-door house, which blocks the sun as it rises. However, I realize the sun will be higher in the sky in the spring and summer and I wonder if there's a way to predict or calculate whether it will clear the house and shine onto my yard.

I know the best way to do this would be to simply observe the yard throughout the seasons and make maps of the sun/shade patterns throughout the day, but I'd really love to garden this year, especially because this is a rental and there's no guarantee of how long I will be here.

We do have a sunny concrete area beside the house where I could grow vegetables and other sun-loving plants in pots, but I'd really like to plant in the yard if possible.

Thanks for any advice or suggestions you may have! :)

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jal_ut
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Location: Northern Utah Zone 5

Re: Calculating or predicting sunlight levels for summer?

Welcome to the forum. If you will edit your profile and include your location it sure helps us to better advise you.

If nothing else, the sun is predictable. Its position can be predicted for any time of any day. Google "Sun Chart".

Of course that is not necessary to grow a garden. Any open spot of any size will receive plenty of sunlight during Spring and Summer. Yes, the North side of buildings will have some shaded area, but when the sun is high the shadows are not too long. Have fun!
Gardening at 5000 feet elevation, zone 4/5 Northern Utah, Frost free from May 25 to September 8 +/-

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digitS'
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Location: ID/Wa! border

Re: Calculating or predicting sunlight levels for summer?

Astralsled, I will do a little thinking outloud and we will see how far I can get ;).

It would be handy if you lived at 45° latitude. Then, you could say that your shadow is exactly as long as your height at high noon on the equinox, March 21st. If you are 5' tall, your shadow will be 5'. If you, or your house is 20' tall, your shadow will be 20' long.

If you live at 0° latitude (the equator), your shadow will be directly beneath you at noon on March 21st because the sun angle is directly above you on that date, at that time. It's 90°, straight up.

You say you don't live on those lines of latitude? That makes things a little more difficult. If you don't need to be too exact, it ain't much more difficult.

Let's say you live on my line at 48°. By the way, Wikipedia will tell you your hometown's latitude ... anyway, on March 21st at noon, the sun's angle will be at 42°, not 45°. Hmmm. How about on June 21st, when the sun will be highest in the sky, here in northern hemisphere??

Okay, the sun is directly overhead that day at noon on latitude 23.5° North. The sun is straight up at 90° but I'm nowhere near the latitude of the tropics! I'm at 48° minus those 23.5°, so I'm 24.5° short of 90° ... oh, so my sun's angle is 65.5° ... see how I got that? Subtracting twice.

Wow! A sun at 42° at noon on March 21st and 65.5° on June 21st. Some day in between, I passed a 45° sun angle when my 20' house cast a 20' shadow! Must have been not too many days past March 21st.

You can deal with any line of latitude and determine the angle of sunlight at noon on those dates. If you are on Denver's latitude at 40° North, the sunlight angle will hit 45° before March 21st. So, heights and shadow lengths will be equal earlier ... not many days earlier, though.

What if you don't know how high your house is? It's fairly simple and you can figure it out anytime the sun is shining. Here is your example:

You know you are 60" tall. Your shadow is 75" long. Your house's height is unknown. The house's shadow is 375" long.

60/75 = X/375

X = (60 x 375)/75 = 300". Your house is 25' tall.

Steve
We are each other's harvest; we are each other's business; we are each other's magnitude and bond. ~ Gwendolyn Brooks

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applestar
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Location: Zone 6, NJ (3/M)4/E ~ 10/M

Re: Calculating or predicting sunlight levels for summer?

DigitS, that was very clear. I sent a copy to my DD to nudge her "little grey cells" a little during this winter break. :wink:
Learning never ends because we can share what we've learned. And in sharing our collective experiences, we gain deeper understanding of what we learned.



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