[TowerTalk] And now for something completely different (TrueNorth)

[Jim Lux]

At 07:52 AM 9/18/2006, TexasRF at aol.com wrote:
>
>Here is a golden opportunity for a talented computer programmer! If Polaris
>makes the rotation as described then it passes right through true 
>north twice
>per rotation. The needed software will tell us just when this happens and we
>can  run outside to complete our exact antenna azimuth calibration.

Easier than you think.. That's what the RA (right ascension) is used 
for. You have to take into account the date and longitude to get your 
local sidereal time (LST). When RA=LST, polaris is directly above the 
pole, when RA is 12 hours away from LST it's directly 
below.  Everything else scales. Polaris appears to rotate counter 
clockwise around the actual celestial pole.

So, the offset (E positive, so it's like bearings) would be 
approximately sin(RA-LST)*(90-decl)

http://en.wikipedia.org/wiki/Sidereal_time

>
>A sub routine can tell us what the offset is on a real time basis so we can
>use Polaris at any time for accurate calibration.
>
>The deluxe version of the program will offer the azimuth for other easily
>recognized stars and the sun as well for a complete suite of calibration
>sources. I bet the telescope watching crowd already have this software.

You may laugh, but a friend assures me that you could do this with a 
cheap webcam and a suitable cheap "department store" telescope and 
some duct tape to hold the whole thing together.  Maybe after the 
smoke clears and I get a chance to sight it with a theodolite, I'll try it.


>
>Who will cash in on this first? I can't wait for my copy of the  program!
>
>73,
>Gerald K5GW
>