Sun tracking formula

picprogrammer · Joined: 10 Sep 2003 Posts: 35

The question is simple, the answer may be very complicated. There are many programs on the web who can caclulate this
http://aa.usno.navy.mil/data/docs/RS_OneDay.php

If i have my Longitude and Latitude the time and date (dcf) i want to calculate the altitude and azimuth of the sun.

A pic processor sun follow system, without ldr or other electronics

Douglas Kennedy · Joined: 07 Sep 2003 Posts: 755 Location: Florida

Look at M l Roderick Land Management Western Australia
" Methods for calculating Solar Position" Technical report 137
They have the code already in c.
Google should find it if you are interested.

crystal_lattice · Joined: 13 Jun 2006 Posts: 164

Maybe this would be of help??
http://www.ccsinfo.com/forum/viewtopic.php?t=17668

Regards

picprogrammer · Joined: 10 Sep 2003 Posts: 35

Douglas, the report you mention is indeed exactly what i need. The only problem is the archive referred in the pdf document cannot be found. It is sunarc2.exe it contains six .c files.

I tried restoring the files from the pdf document but the are so many misspells it cannot be compiled.

crystal_lattice · Joined: 13 Jun 2006 Posts: 164

Hi there I might have a solution to your missing files problem: Do a search for "web archive" you will find a site where you can type in the url of the file you want. This site archives files allover the net, you might be lucky and find the files there - it worked for me on numerous ocasions.

I have a question of my own though: Does a algorithm exist to track stars? eg. connect your telescope to pan/tilt unit, set your date/time/co-ordinates in to the unit, find your star and sit back and relax! Anyone tried this before??

Regards

Douglas Kennedy · Joined: 07 Sep 2003 Posts: 755 Location: Florida

Star position moves with the flow of sidereal time ( there is an extremely small precession correction that is neglected unless you are a major observatory ). The mean sun moves with the flow of universal time(GMT). The number of times a star is over head per year ( assuming it is visible from your latitude) differs by one from the number of times the sun is overhead. That means compared to solar days sidereal days are shorter by approx 4mins (24hrsx60/365.24). The earth also varies from a circular orbit creating the apparent speeding up and slowing down of the sun as it moves in the sky through out the year so universal time is based on an idealized average (mean) sun. Sidereal time flows with the spinning earth so good news no solar corrections.http://library.thinkquest.org/29033/begin/time.htm

crystal_lattice · Joined: 13 Jun 2006 Posts: 164

Hi Douglas, i feel you answered my question, but i don't comprehend the terminology you used. What i understand is that you could set your scope on a star and let your pan motor rotate opposite to the earth at the same rate/speed?? What happens to the angle formed by earth compared to star optical path. Not sure if i'm explaining it correctly.

PS. my browser is having problems to load the link you provided.

Regards

Douglas Kennedy · Joined: 07 Sep 2003 Posts: 755 Location: Florida

Depending on you latitude a star can rise and set. Some stars will not set
Ex in the Northern Hemisphere the pole star will never set (but the sun will rise and make it too dim to see) others will never rise Ex Southern cross.
If you set your axis parallel to the axis of the earth then all the stars you can see from your latitude will cross the sky at a sidereal time flow ( one hour is 15 degrees). Now the earth's axis is inclined ( tilted) relative to the plane of its orbit around the sun. So just as the sun gets higher in the sky during a northern summer so will the stars relative to your horizon. Further each night the hemisphere of stars that you can see alters because you are making the yearly trip around the sun. There are much much better descriptions than I could ever give of this on the web including some animations. If your tracking device rotates around an axis parallel to the earth's at a rate equal to the flow of sidereal time and if you alter the elevation to point to a chosen star that star will be tracked that night.

crystal_lattice · Joined: 13 Jun 2006 Posts: 164

Thanx Douglas, that makes more sense, am no astronomer but will consult the web for more detail. My previous setup attempt would have used image recognition linked to a digital camera/scope setup. The image recognition software will have a wide focus and try and keep the star within a predefined "boundary" by moving the pan/tilt. I think the algorithm method might be simpler to implement. Anyone tried it before?

Regards

Ken Johnson · Joined: 23 Mar 2006 Posts: 197 Location: Lewisburg, WV

Not the answer to your question, but . . . the image recognition approach will require an error before it can correct, introducing "wobble", whereas the algorithm will track accurately with no (rather, minimal) error.

Ken