[Date Prev][Date Next][Thread Prev][Thread Next] - [Date Index][Thread Index][Author Index]

Sun and Instant Track - errors - unclassified

Not much to do with satellites, or is it???

Over the weekend I was using IT to predict the azimuth and elevation of the
sun at various hours UTC.
(My eldest son, just a few weeks into his High School career, was designing
a sun dial...)

It became apparent that the azimuth and elevation figures from IT were
sometimes different if I:
(a) let the systems run up to the hour, or
(b) used the T function to enter an hour and calculate an observation (i.e.
a one-time calculation).

It seemed that the one-time calc (T function) gave the 'correct' azimuth
(see method under). This was most apparent when IT was free-running at a
minute or two either side of the hour then I entered T and the hour/minute.
The angle would sometimes jump by 5-8 degrees.

My concern is that IT (or my computer) may be creating a regime of errors.

Has anyone any ideas on what is going on here?


- We established a 'sun dial' with the axes aligned true N-S / E-W.
- On the hour, we observed the sun azimuth and marked the shadow of the
gnomon (the post of the sundial).
- We measured the angle from true north with a protractor.
- We used IT to calculate / check / predict the angles.

     _  .      Peter R. Ellis, Amateur Radio Op. VK1KEP
   _-' |_|\         at Canberra, Australian Capital Territory
  /        \        email: peter.ellis@dao.defence.gov.au
  \_.--._ C/
         \/         RNARS Australia (see also http://come.to/rnars/)
VK1KEP:     http://www.geocities.com/CapeCanaveral/5796/vk1kep.htm
Personal:   http://www.geocities.com/CapeCanaveral/5796/pre-pers.htm