If I were going to erect a greenhouse, I'd put it where the most sun shines during the period I wanted to use it.

Not quiet ready to come back.

By 'East West line' you mean the line through the East and West points of the compass. (Not the magnetic compass.)

The Sun rises due East and sets due West on the Vernal and Autumnal equinoxes. By definition, that gives us 12 hours of night and day. During its summer, each hemisphere gets more than 12 hours of daylight, but from the time in the morning when the Sun is due East until the time in the evening when the Sun is due west there are exactly 12 hours. If you have trees or buildings obstructing your view of the East and West horizons you may not see the full 12 hours.

If you can find a website that will tell you when local noon is for your location, i.e., the transit time for the Sun at your location on Earth, then you can just subtract and add 6 hours to get the time when the Sun is due East and due West.

Yes, the compass, not the magnetic compass. Actually, I thought it was 12 hours or perhaps more than 12 hours with the sun south of that line up until sometime yesterday. I made a little physical model. It showed me that the combination of the tilt of the earth in summer with the spin of the earth means the sun crosses that line earlier. (from the tropics to the northern circle) But I would welcome certainty. I might easily have goofed. Anyway, if anyone has the necessary software or table of figures, Sun angle from 90 to 270 is south of the line and anything else is north of the line. I tested for something like 50 degrees latitude. You get those figures online for sunrise and sunset but I have not found them for the sun path yet. Thanks Brian

compass:

• North (N): 0° = 360°
• East (E): 90°
• South (S): 180°
• West (W): 270°

You are in the Nothern hemisphere! There should be more sun coming from the South of the East West line unless there is a tree line or you are over the arctic circle where you can choose for some part of the year where "South" is. I thought over summer (please define summer) the 12 hours are a given for all of the area that is tilting angle of Earth axis away from the Equator. So where exactly are you that makes it less? Because I can not think of a place like this that gets sun from the North. Am I missing somehting?

But any sun coming from the North will be at a low angle. This will not warm up your green house. I think the best catch is South East. The reason is a rather easy one. You want the green house to warm up with the earlier sun. This way you can use it longer and dont have to wait for the sun to come around.

Only my 2 cents

IS

I was having summer as March equinox to September equinox. I thought pretty much the same as you until yesterday. (But I guessed that it might be more than 12 hours to the south. I might well have made a mistake but when I moved my earth model for about 50 degrees northern latitude (with laser level to point to the "sun") to equinox at 6pm (sundown) and then raised the sun to 15 or 20 degrees, ( earth tilt sometime in summer) the laser point moved into the northern half. I had to bring the "time" back by over an hour on the degrees or earth rotation to bring it back to the 270.

I admit that this is really hokey. It was just a tripod for taking levels Tilted back at 50 degrees and a dot from the laser level to be the sun. The 360 degrees on the tripod was for the hours of earth rotation. and the laser level bubble goes level when it is sun up or sun down.

Actually, I am going to check it again right now.

If I haven't screwed up, it is an interesting finding. An astronomer could clear it up in a heartbeat.

Brian

Yeah, checked again, my degrees on the laser tripod go the other way. But apart from that, I think it is a correct model. It is not a big effect but you definitely have to adjust back on the "clock" to get to the east west line, when you adjust the 'sun" for summer from equinox. And I am fairly sure that straight up is vertical on my model too. So it still shows less than 12 hours of sun to the south of the east west line in summer.

Thanks

Brian

Hey there Brian,

Glad to hear you got your green house built - post a picture if you can!

Try this link. If I've interpreted your question correctly, it should help.

Regards - KJK

Let me correct my earlier comments and give you some info that might help. I used an astronomy program set to the position of Nottingham, UK, to plot the sunrise, sunset, due East, due West, and transit info for the Sun, and to see what the local civil times (wall clock times) would be for the Sun at these positions. These times and locations are approximate, but reasonably close.

On this date, at 53 degrees North (for Nottingham), the Sun rises at 4:48 AM at a point of 50 degrees azimuth. It reaches the due East position, 90 deg azimuth, at 8:23 AM. It transits the meridian at a civil time of 1:08 PM (the time on your wall clock).

It then reaches the due West point (270 deg azimuth) at 5:52 PM, and then sets at an azimuth point of 310 degrees at 9:25 PM. Total daylight hours is 16 hours, 37 minutes. The Sun spends 10 hours and 37 minutes in the 'South' part of the sky, between 90 and 270 degrees azimuth. It spends 3 hours and 33 minutes in the Northeast part of the sky and 3 hours and 35 minutes in the Northwest part of the sky.

Here are a couple diagrams.

Due East position:

Due West position:

The program I used is 'Starry Night'.

Thanks for that. And especially big thanks for following up. Well done.

Before this weekend, I would have bet it spends at least 12 hours in the south part of the sky (and probably more than 12 hours) especially in summer.

And I must admit, if someone else had posted that question a week ago, I would have mildly suspected him of been a bit of a whacko.

Anyway, (in answer to another post in the thread), relating this to lean-to greenhouse design is more about the amount of light you get for the plants in the day than the heat you get. Thanks again for the help.

It means a lot

Brian

if You are situated North of Equator then received advice to put the greenhouse so it is open to sunlight from east, south and west is correct. If You are located below, South of Equator, then naturally sun at noon tends to be on North side. To have Sun rise to NorthEast and set at NorthWest, You would have to be on New Zealand, in Argentina or even Antartica. or You have severe magnetic anomaly that screw Your compas readings. Simpler still, You may have something metalic that skew kompass reading.

Please next time provide pertinent data such as geographic location so people can understand Your position.

GO BACK AND READ THE OTHER POSTS. YOU ARE WRONG. (And be good and say sorry while you are at it). " To have Sun rise to NorthEast and set at NorthWest, You would have to be on New Zealand, in Argentina or even Antartica". Sorry, buddy, you failed the reading test. On this date, TODAY the sun is rising in the north east in parts of Norway, Scotland, and Russia and northern Canada. This is a screenshot of an area of Victoria BC on 15th june taken in sollumis.com It even shows on the left where the sun is rising. If you want to cross reference it, all the other sites give the same result. Have some fun with it, check your place on different dates. It is educational.

Mr. GAIATECHNICIAN, This is first time in my life I heard something like this. I understood that You are saying that at noon You have sun at North. Next it is summertime now, so clock is set up one hour later than actual time (Daylight Saving Time), which may be the reason for for seemingly wrong time for pass of Sun over meridian. Also, when I was answering Your post, I did not see any other answers at all, there was just Your OP and I was supposed to answer You first.

I was making astronomy program some 30 years back to list Effemerides, and such rules were walid then, as well as in World Atlas from this time. Perhaps some facts were updated in the meantime, and anyhow I am now living in different country without ever moving from my house, so anything is possible, or this is because it is year 2012 and Earth is about to shift magnetic poles.......

In any case I have had one sleepless night behind me and perhaps my brain did somersaults so I have mistaken extreme South while it is almost extreme North.

But I never lived other than in my country so such phenomenas are not known to me nor anybody I know, and I never saw them mentioned in the astronomy books, except for known phenomeny of having 6 months day and 6 months night in some extreme latitudes.

In any case Geographic East and West, North and South do not match same points by compass. We are also nearing the longest day of the year, when night is shortest, therefore there has to be more hours of sunlight than 12 hours of equinocii that happen only twice in a year..

Now, I am really sorry, sorry that I bothered and spent the time trying to help.

You should have simply observed for few days and simply put sticks in ground at such angle that there would be no shade of the stick on the ground.

Unfortunately IMHO Your requirements overlap, as there is most of sunlight and heat together and You cant get one or other separately.

We programmers would in such case invoke rule # 17: " If nothing else helps, look into the manual" in this case for setting up Greenhouses...........

Regards from homeland of Nikola Tesla!

Ok, sorry, English is your second language and I mangle it so I probably explained thing pretty badly. If you check the whole thread, it gives a better idea of where things are going.

Thanks

Brian

If I may suggest that You make windows on the West sloped at 29 degrees or less, while You make verticall windows to the East, that would capture morning light and reflect away afternoon light, thus augumenting heating in the morning and precluding overheating in the afternoon. Likewise if You want to make noon heat less, then roof windows has to be at slant of 30 degrees to direct ray of the Sun or less, then most of noon light and heat would be reflected. If I remember it correctly,

Sun is at 23 degrees above horizon at noon on equinocii going to maximum 36 degrees in summer and down to 10 degrees in winter. Angle of window has to be at 30 degrees or less to ray of the Sun to be reflected away.

So, I would put Eastern wall at slant of 100 degrees, Southern wall and the roof united at slant of 110 degrees and Western wall at 100 degreees facing west.

If greenhouse is stand alone then Northern wall should mirror Southern wall at 80 degrees slant facing north, else it would be side of the house. It can be covered with mirrors facing inside of Greenhouse to reflect light back to it from that side of Greenhouse that would othervise escape ir be absorbed by the wall.

That would make Greenhouse optimized for winter time to receive as much light as possible, and light get reflected mostly at summer time at noon. In addition, light get reflected from opposite side of the wall trough which light enters, from inside and is directed at the ground. If You prefer, it could be made piramid shaped with all valls and roof at same 110 degrees angle, but it would then be symetrical only as standalone structure. May be more simple to build as sides are roof also. doors could be on Northern side, and it can have two or more levels.

That's a very interesting site, Brian,(sollumis.com)and something I didn't know when I built my home. I became aware of it because it's obvious from the angle of light that enters the windows at different times of year.

There is a practical reason for orienting a greenhouse East or Southeast which isn't obvious without experience. My own greenhouse is oriented due south, and doesn't get early morning light because of obstacles - heavily forested that side. It gets lots of sun from the west because there are no obstacles, so there's lots of capture in the afternoon. Trouble is, the greenhouse is already hot after the noonday sun, and doesn't need the extra rays so much. More direct sun in the morning would warm up the space that has cooled overnight, when it's really needed. A bit of shade in the west would prevent the space from overheating later in the day. If I were building today, I would probably choose a southeasterly exposure for that reason.

As you pointed out in your earlier post, the climate where you're living doesn't require a lot of heat capture in summer, and as I understand it the function is more as a wind shelter than a solar capture design. Are you finding that the north sloping glass picks up early morning and late afternoon sun from the NE/NW angles? How does that affect the overall temperature-moderating function of the greenhouse?

So far it is working well but it has been a crappy summer. I am a bit concerned that I even used sollumis because it gives no information about who provides it and they have no email address ( for instance to tell us what the rays stand for). Other sites do confirm their figures but nobody else does the little visual thing and that sets it apart. I know what you mean about heat but maybe that is more a ventilation thing than anything else.

When I made the thing the suggested best option was stand alone. (Not an option for me). and then eastern or southern facing lean to and after that western facing lean to.

And all these are shown as leaning down to the south. But if you lean it back to the north, the roof acts favourably to bounce off more noonday sun (Possibly a good thing because it bounces heat away too) and it also is a lot better at catching the low angle sun coming in from north of east in the morning and from north of west in the evening. I include the graph to show how glass transmits or reflects more or less light depending on the angle of the glass in relation to the light. Anyway, I contend that this captures significantly more light than a typical lean to greenhouse (This can be checked by the right people with the right software) and I believe that we as a society got caught up in copying each other and everyone does everything the same because of this. Anyway, I would have done a lean to but I screwed up. Things were already too high before I did the roof. My greenhouse may never amount to anything but perhaps we can learn from it. Like you said, it is an interplay of light, heat shelter and climate. My lean away gets a heck of a lot of light in summer.

Brian

towards the light.

I will put a diagram of the site on too. Anyway, it is a highly unusual site and the 5 pieces of glass also constrained me. I now have veggys growing in front and on the side going to the rain barrel. Brian

So, anyway,the question is answered! in the northern hemisphere north of the tropics, (except at equinox), the sun ALWAYS spends LESS than 12 hours in the southern half of the sky! It only rises in the east at equinox. I think "rises in the east and sets in the west" is religously set in our heads as kids. I am going to try to insert 4 screenshots from stellarium to show the case for June the first. hopefully you can see the grid lines for degrees. First one is dawn. Note the times. and the next one is as the sun crosses the east west line into the southern half of the sky.

Again note the time on the time date thingy. Next up is the sun crossing into the northern half of the sky again. And finally dusk

So anyway, this strengthens my point. I made a greenhouse on the south side of a fence because I had only enough glass for 3 sides. Luckily it leans up to the south from the fence so it catches much of the direct light from the northern half of the sky. If it had been put on the east or south of a building and lean down from the building, (as recommended for lean to greenhouses!) Almost all of this direct light from "over the fence" would have been lost! Anyway, I highlighted this finding here, on instructables (the greenhouse got featured on their homepage), on youtube and elsewhere but reviewing the viewing figures, they are pathetic. Even the permaculture people don't seem to give a crap. It seems that the tradition of "common sense" (putting your lean to greenhouse in the wrong place) is going to continue regardless of findings like these. I guess it is a lost opportunity. Just a shame that no leaders in greenhouse siting have taken note. Brian