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measured difference in azimuth of Sun?



 
 
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  #1  
Old August 2nd 03, 03:12 AM
Odysseus
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Posts: n/a
Default 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
  #2  
Old August 2nd 03, 08:29 AM
Aditya Naredi
external usenet poster
 
Posts: n/a
Default measured difference in azimuth of Sun?

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.
  #3  
Old August 2nd 03, 08:29 AM
Aditya Naredi
external usenet poster
 
Posts: n/a
Default measured difference in azimuth of Sun?

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.
  #4  
Old August 2nd 03, 09:12 AM
Paul Schlyter
external usenet poster
 
Posts: n/a
Default measured difference in azimuth of Sun?

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/
  #5  
Old August 2nd 03, 09:12 AM
Paul Schlyter
external usenet poster
 
Posts: n/a
Default measured difference in azimuth of Sun?

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/
  #6  
Old August 2nd 03, 11:00 PM
Odysseus
external usenet poster
 
Posts: n/a
Default measured difference in azimuth of Sun?

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
  #7  
Old August 2nd 03, 11:00 PM
Odysseus
external usenet poster
 
Posts: n/a
Default measured difference in azimuth of Sun?

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
 




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