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Sun angle and sun path

Sun angle at 37 degrees latitudeYesterday I wrote that our new porches tempt me and Mark to spend more time relaxing outdoors than we used to.  As a result, we've been paying more attention to the natural world, and, after a couple of weeks, I made a shocking dicovery.  The summer sun rises in a totally different spot than the winter sun does!

Yes, we technically already took advantage of this fact when we planned our south-facing trailer windows to capture winter sun without roasting us in the summer.  And if you'd asked me a year ago, I could have told you that the sun is lower in the sky in the winter than in the summer.

Sun path for 37 north latitude

But I didn't realize that the sun being higher in the summer sky means that it rises over the barn instead of over the hill like it does in the winter!  This tidbit of data makes our budding passive solar heating and cooling systems a bit more complex.

Porch shading houseNotice how our new porch shades the East Wing from the morning sun.  I was a bit concerned that we'd be losing some much-needed winter solar gain, but overlaying the sunpath diagram with a map of our property shows that the sun has moved so far south in the sky by late fall that it barely hits the side of the east wing at all.

By the same reckoning, we could probably block some of the scorching late afternoon sun on the west side of our trailer without impacting winter solar heat gain as well.  I'm still Sunrise and sunset at the winter solsticewrapping my head around the fact that the sun doesn't rise in the east and set in the west, though, so I think I'm going to observe a little longer before I make any drastic decisions for that area.

If you want to play with sun patterns in your own neck of the woods, there are lots of good resources on the web.  This website allows you to calculate the sun angle at your latitude (but you'll have to draw the elevation mockup yourself) and this website has downloadable sunpath diagrams, like the second image in this post.  Finally, this website allows you to plot sunrise and sunset locations overlaying an aerial photo of your property for any day of the year.

Or you can just build a porch and watch the world unfold around you.

Our chicken waterer never spills in uneven terrain, so it's much safer than traditional waterers in chicken tractors.

Trailersteading

Edited to add:


Read more about passive solar design in Trailersteading, which is now available for $1.99 on Amazon.  I hope you enjoy reading it as much as I enjoyed writing it!



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I find it easier to visualise this in 3D. This is were a bit of knowledge from astronomy comes in handy. Take a globe with a tilted axis, and draw lines on it by rotating the globe on its axis with a marker held horizontally. Do this in different orientaties w.r.t. the rotation axis of the earth, and you'll see that the projection of the sun on earth is a circle of a sphere on different latitudes.

Public observatories and science museums generally have displays that describe the ecliptic versus the celestial equator. Another insightful tool is a good orrery.

BTW, the sun does rise in the east and set in the west, but only on the equinoxes. :-)

Comment by Roland_Smith Tue Jul 10 13:28:12 2012

A very powerful tool for determining where shadows will fall on a structure is Google SketchUp. You can get some rough dimensions (the more accurate the better) and model things quickly and then change the time of day as well as time of year, and it will update automatically so you can see where the shadows fall with different length overhangs etc. A 3D visualization is a very helpful tool.

It would be nice to be able to do the same thing with trees on a property but it would be very difficult and time consuming to model.

Comment by Brian Tue Jul 10 15:28:49 2012

Roland --- You're right on track --- seasons have always seemed like a mystery to me. No matter how hard I try to wrap my head around the tilt of the earth, I can't seem to make that 3D visualization work. Sounds like I'll have to track down one of those displays in a museum and see it for myself.

I did learn about the ecliptic just this past winter, which was handy. And I did finally realize while making this post that the equinoxes would be the time when the sun rises in the east. Yes, I'm slow... :-)

Brian --- I've been tempted by Google Sketchup many times, but they don't support Linux and I'm never tempted enough to boot to the evil Windows side of my computer. Plus, I suspect it would be tough to really make shadows for our farm since we're encircled by hills and trees of different heights. Maybe someday I'll head to Windows and give it a try....

Comment by anna Tue Jul 10 19:56:20 2012

Heres a video of how easy it is to show where shadows are cast different times of the day and of the year.

http://www.architectionary.com/TutorialsShadows

It wouldn't take long to do a model of your house and see how different size/height/location awnings or porches would effect the shading in different seasons.

I don't think I would use it to model all the trees on your property but for awnings and overhangs I think it would be useful.

If you ever reboot give it a try.

Comment by Anonymous Wed Jul 11 18:18:48 2012
Anonymous --- Yep, does sound pretty simple if your terrain is simple. I haven't booted to windows in about two years, though, so I suspect I won't go there anytime soon. :-)
Comment by anna Wed Jul 11 18:54:06 2012

I did sunpaths for my property last year as part of my permaculture design certificate, and can confirm that the theory did match what actually happened through the seasons :-).

I just bought a trail camera (I think you have one, Anna?) and it has a feature to take timed photos throughout the day. Next winter and summer solstice, I'm going to set it up in my yard and photograph a day's worth of shadows, so I can get a really good idea of where they actually fall through the day.

Out of interest, Google recently sold SketchUp to Trimble. It works on Mac too, so there is a good non-Windows option :-).

Comment by Darren (Green Change) Wed Aug 8 23:11:34 2012
Darren --- I read your post about using a trail camera for that --- great idea! I'll have to see if ours has a time lapse feature and use it for the fall map!
Comment by anna Thu Aug 9 08:18:43 2012

Just wanted to let Anna know that there is as linux based program to help visualise the earth and sun, moon movements in relation to each other. It is called Openstereo and here is their web link http://openstereo.sourceforge.net/.

Good work on your site its great to seeing people become empowered harmoniously with our environment as much as possible. As a side note I have been using Linux Mint as my operating system due to is non commercial purpose i.e. it costs nothing. I did this 5 years ago to support sustainable practices. Ill tell you from my own experience its way more reliable and simple to use than Windows ever was.

I know this is off topic somewhat but think its one main area most of us who use technology fall short. And we could become independent in that regard.

Comment by Free Tech For All Mon Jul 29 05:48:24 2013