measured difference in azimuth of Sun?

Aditya Naredi wrote:

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..

[snip]

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?

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

Aditya Naredi ) writes:
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.

Would really appreciate your help.

Thanks in advance,
Aditya

Since 15 degrees of longitude is one hour of clock time, did you allow for
daylight saving time?

--John Park

Thanks for your followups. Please see my comments inlined:

\(formerly\)" dlzc1.cox@net wrote:
A compass cannot do true north. It can do magnetic north, and that can be
affected by local phenomenon.
David A. Smith"

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

Thomas McDonald" wrote
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

would definitely try that.

Odysseus wrote in message
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.

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,
Aditya.

In article ,
Odysseus wrote:

Aditya Naredi wrote:

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..

[snip]

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?

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.

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/

Aditya Naredi wrote:

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).

Sorry, I didn't read your table carefully enough.

--
Odysseus