Thursday, Mar 27, 2008 at 14:29
That is precise enough! ;o)
For those who want to be exact - a short astronomy lecture.
The equation at local noon is Altitude =90º-(Latitude - Declination) where lat and dec have the same sign.
(This is why noon sights were so important in the days of sextant navigation. The sextant gave the altitude and you got an immediate readout of your latitude with simple addition and subtraction. Once the sun left due north (or south) you entered the realms of spherical geometry and accurate clocks to work out where you were)
eg today in
Adelaide:
Latitude = 35ºS
Sun's Dec = 2.7ºN
Therefore panel angle at local noon (11:54 today) =90-(35-(-2.7)
=90-37.7
=52.3
So the panel should point north 52.3º above the horizontal at 11:54 am for maximum effect. (except it was clouded over and raining)
On the winter solstice the sun is only 31.5º above the horizon at in
Adelaide at local noon.
On the summer solstice it is 78.5º above the horizon.
Which is a fair range and why a better sundial will have a correction table for the date.
In practice I just make sure the panels are pointed towards the sun then just angle them to make the largest shadow and move them when I think of it. If I am there more than one day I set them up after sunset to catch the morning sun.
Here endeth the lesson. :o)
Cheers
Pete
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