# Thread: measured difference in azimuth of Sun?

1. ## measured difference in azimuth of Sun?

Hi everyone,

A few days back I heard from my hometown in India that people
observed a 'northern shift' of Sun during sunrise. This happened
around July 17th (2003). Unbelievable as it seemed, I proceeded to
measure it myself as follows..

I calculated the angle the shadow of a vertical body made with
True North (determined by a compass) at different times and
different places in Seattle (USA). I compared this angle
(that Sun makes from true north - called 'azimuth') with the
calculated angles posted on numerous official and unofficial
websites, and I found it differing exactly by 15 degrees.

Here are the results:

Data:
Magnetic declination in Seattle (19 degrees East)
Place Seattle, WA USA (122 20 W, 47 38 N)
Calculated data taken from the website: http://aa.usno.navy.mil/data/
(US Navy?)

I was careful the measurements were taken in a magnetic influence
free environment.

Date Time Measured Calculated Difference
(with True North) (from website)
----------------------------------------------------------------
07/29/03 15:30PM 235 degrees 250 degrees 15 degrees
07/30/03 10:46AM 124 degrees 140 degrees 16 degrees
08/01/03 16:40PM 250 degrees 264 degrees 14 degrees

Obviously the first thing that comes to my mind is that the
calculations are wrong (wrong caliberation of compass etc), or direction
of Magnetic Pole changed here in Seattle - but since the same difference
has been observed in other places too, I don't think that's the
case.

Can someone please measure Sun's azimuth at their places and let me
know if it differs from calculated azimuth or not? If it is, what are
the possible explanations? If not, what am I doing wrong?

If these observations are correct, it would be interesting to measure
measure altitude / azimuth of Polaris. I don't have any instruments
to do that right now - am working on it.

2. ## measured difference in azimuth of Sun?

I think you might call a local observatory or active amateur astronomer
and ask them if their telescope pointing software is laying their telescopes
on target.

If you have a telescope (lowest possible power) or binoculars on a
relatively steady mount, you can aim it at Polaris and lock it down very
well. Check it frequently. If Polaris stays in the field of view, the
world has not tilted. (Remember that Polaris is off-set from true north by
not quite a degree; some shift in postion might be noticed; but if things
are as bad as you and your friends in India fear, Polaris would move out of
the field of view pretty quickly.)

If you don't have a 'scope, you could fix a long straight-edge to a
sturdy vertical surface (tree, post, etc.) aimed directly at Polaris. This
would accomplish the same thing as above.

You will find that the sky has not, in fact fallen; and that you and

Tom McDonald

3. ## measured difference in azimuth of Sun?

[snip]
The first thing I'd suspect is that the sunrise positions you looked
up were just the "geometrical" azimuths. Atmospheric refraction and
other effects not included in such figures can make a very large
difference to the observed position. Moreover, I imagine that looking
north-east from Seattle the horizon is pretty mountainous; you might
do better trying to observe sunsets over the Juan de Fuca Strait.

--
Odysseus

4. ## measured difference in azimuth of Sun?

"dlzc@aol.com \(formerly\)" <dlzc1.cox@net> wrote:

I know about that, I adjusted 19 degrees for Seattle's magnetic declination to
get true north from magnetic north.

Thomas McDonald" <tsmac@wwt.net> wrote

would definitely try that.

Odysseus <odysseus1479-at@yahoo-dot.ca> wrote in message

well, I measured this at different times of the day so its not always sunrise.
Atmospheric refraction shouldn't affect this at noon (even if it does in small
degrees, it would affect altitude, not azimuth). This also means that I'm not
always looking north-east from Seattle (actually its south-west in afternoon).

Guys I really appreciate your responses. But did any of you actually try to
measure it yourself? I'm 100% sure, you'll notice this difference too. Could
you please? That's just 5 minutes out in the Sun!

Thanks,

5. ## measured difference in azimuth of Sun?

Since your discrepancies are very near 15 degrees, I strongly suspect
an error of precisely 1 hour in time in your computed values. Perhaps
you forgot to account for Daylight Savings Time? Or perhaps you used
the wrong time zone? It's hard to tell which, since you don't give enough

I can assure you that Polaris has not shifted azimuth by 15 degrees.
My country house (where I am right now) is oriented precisely
in the north-south direction (within a degree or better), and Polaris
was at its usual direction in the sky last night relative to that
house. I would immediately have noticed a shift of 15 degrees....

Also, my sundial in the garden shows correct solar time still. It
would have been one hour off if there had been a 15 degree shift in
solar azimuth.

Finally, a 15-degree shift in solar azimuth would also put the narrow
zones of total and annular solar eclipses on the Earth's surface 15
degree off their predicted values, making expeditions to these solar
eclipses miss their targets -- and that would be BIG NEWS !!!!!

--
----------------------------------------------------------------
Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
e-mail: pausch at stockholm dot bostream dot se
WWW: http://www.stjarnhimlen.se/
http://home.tiscali.se/pausch/

6. ## measured difference in azimuth of Sun?

In article <3F2B1DFC.489E5BC1@yahoo-dot.ca>,
Odysseus <odysseus1479-at@yahoo-dot.ca> wrote:

He didn't measure this at sunrise - check his data:

# Data:
# Magnetic declination in Seattle (19 degrees East)
# Place Seattle, WA USA (122 20 W, 47 38 N)
# Calculated data taken from the website: http://aa.usno.navy.mil/data/
# (US Navy?)
#
# I was careful the measurements were taken in a magnetic influence
# free environment.
#
# Date Time Measured Calculated Difference
# (with True North) (from website)
# ----------------------------------------------------------------
# 07/29/03 15:30PM 235 degrees 250 degrees 15 degrees
# 07/30/03 10:46AM 124 degrees 140 degrees 16 degrees
# 08/01/03 16:40PM 250 degrees 264 degrees 14 degrees

The Sun doesn't rise, or set, at 15:30PM, 16:40PM or 10:46AM in July
at 47 deg N latitude....

Since his discrepancies are all near 15 degrees, my first guess is
that he made a "one hour mistake": either forgetting to account
for Daylight Savings Time, or by mistake choosing the wrong time zone.

--
----------------------------------------------------------------
Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
e-mail: pausch at stockholm dot bostream dot se
WWW: http://www.stjarnhimlen.se/
http://home.tiscali.se/pausch/

7. ## measured difference in azimuth of Sun?

Go back and look at the Naval Observatory tabulations ... they are
for Pacific Standard Time, not Pacific Daylight Time ... using
those tables
Date PDT Your measure PST USNO Diff (O-c)
07/29/03 15:30PM 235 degrees 14:30PM 235 deg 0 deg
07/30/03 10:46AM 124 degrees 09:46AM 121 deg 3 deg
08/01/03 16:40PM 250 degrees 15:40PM 253 deg -3 deg

Looks pretty normal to me.

8. ## measured difference in azimuth of Sun?

pausch@saaf.se (Paul Schlyter) wrote in message news:<bgfro9> >

you are right, the websites I looked at used PST - not accounting for daylight
saving time. That explains it.

Thanks a lot for your help,

--
Odysseus

10. ## measured difference in azimuth of Sun?

Plus, I would think, common sense wise, that if the
sun had shifted its position in our sky (which means
a shift in the earth) the Big Boys out at Kitt peak,
et al...who track the sun all the time, plus the solar
satellites, something of that nature would have made
FWIW,
Tom W.