Initial mounting a scope due North?

Hi Folks
I am equatorially mounting a scope onto a steel pier in an observatory.
I have about 10degs of adjustment in azimuth and want to mount it
initially due North and then adjust it by the drift method afterwards.
I have to drill and tap three holes into the flat plate on the pier and
one of them is directly under the RA axis ie pointing North. My idea is
that if I can make a vertical thin bar cast a shadow at noon GMT ie
1300 BST then this will point due North enabling me to mark on the
plate for my first tapping. There is too much metal and steel about to
get an accurate compass reading and of course trying to do it at night
time its too dark. Where I live is about 1deg west longitude, should I
make allowance for this?. Does this sound feasable or just plain
cobblers ;-)?
Cheers
Steve

Hi Steve,

I'm no expert but I'm not sure 'noon' is always at 12 GMT.

If you can find out what time local noon is and mark the line at that time
it should work.

You might have to take a few measurements at local noon over a few days to
be sure.

Failing that, try to borrow a GPS with a compass.

Michael.



"Steve" wrote in message
ups.com...
Hi Folks
I am equatorially mounting a scope onto a steel pier in an observatory.
I have about 10degs of adjustment in azimuth and want to mount it
initially due North and then adjust it by the drift method afterwards.
I have to drill and tap three holes into the flat plate on the pier and
one of them is directly under the RA axis ie pointing North. My idea is
that if I can make a vertical thin bar cast a shadow at noon GMT ie
1300 BST then this will point due North enabling me to mark on the
plate for my first tapping. There is too much metal and steel about to
get an accurate compass reading and of course trying to do it at night
time its too dark. Where I live is about 1deg west longitude, should I
make allowance for this?. Does this sound feasable or just plain
cobblers ;-)?
Cheers
Steve

BT News wrote:
Hi Steve,

I'm no expert but I'm not sure 'noon' is always at 12 GMT.

It Isn't - it varies roughly upto 15mins on either side throughout the
year.

This should help: http://en.wikipedia.org/wiki/Equation_of_time


--
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Dorset UK Info, Meeting Dates, Sites & Maps
Change 'news' to 'sewn' in my Reply address to avoid my spam filter.

Cheers for that.
I`m sure the azimuth adjustment I have would be ok for 15mins
difference. It was just an initial mark I wanted.
Thanks again
Steve

"Steve" wrote in message
ups.com...
Hi Folks
I am equatorially mounting a scope onto a steel pier in an observatory.
I have about 10degs of adjustment in azimuth and want to mount it
initially due North and then adjust it by the drift method afterwards.
I have to drill and tap three holes into the flat plate on the pier and
one of them is directly under the RA axis ie pointing North. My idea is
that if I can make a vertical thin bar cast a shadow at noon GMT ie
1300 BST then this will point due North enabling me to mark on the
plate for my first tapping. There is too much metal and steel about to
get an accurate compass reading and of course trying to do it at night
time its too dark. Where I live is about 1deg west longitude, should I
make allowance for this?. Does this sound feasable or just plain
cobblers ;-)?
Cheers
Steve


Steve,

We had to do much the same at University of London Observatory in order to
re-mount one of the telescopes in a new dome in 2000.

What you need is the UT of the apparent solar transit at your location each
day. You can use the time of apparent noon at Greenwich each day, plus
knowledge of the exact longitude of your observatory. To get this to the
nearest second, you will need the Astronomical Almanac or at least a copy of
the relevant page. The error involved will be at most a couple of seconds
of time--if that--due to RA movement of the Sun between Greenwich and your
location about 1 degree W. If you use the longitude difference in *solar
time* you more or less correct for solar RA drift over the small time
interval. The better you know your exact longitude, the better this will
work. (Usually, for stars, you would use the difference in *sidereal time*
but for the sun use solar time intervals.)

Also, you need an accurate clock, good to ±1 sec.

Our final azimuth error was 18 arcmin, mostly due, I think, to errors in the
actual hole placements on the concrete pillar, e.g, caused by small
misalignments of telescope base template prior to drilling, the diamond
drills, the adhesive, bolt positions, etc. With 10 degrees to play with,
you have some room for mistakes. We had a maximum adjustment of around ±1.0
degree, so considerable care was justified. OTOH, you want your mount to
look nice and tidy, not canted at a large azimuthal angle.

Our procedure is described here.

http://www.ulo.ucl.ac.uk/telescopes/fry/fry_align.html

--
Mike Dworetsky

(Remove "pants" spamblock to send e-mail)

JRS: In article . com,
dated Sat, 23 Sep 2006 04:07:06 remote, seen in news:uk.sci.astronomy,
Steve posted :

I am equatorially mounting a scope onto a steel pier in an observatory.
I have about 10degs of adjustment in azimuth and want to mount it
initially due North and then adjust it by the drift method afterwards.
I have to drill and tap three holes into the flat plate on the pier and
one of them is directly under the RA axis ie pointing North. My idea is
that if I can make a vertical thin bar cast a shadow at noon GMT ie
1300 BST then this will point due North enabling me to mark on the
plate for my first tapping. There is too much metal and steel about to
get an accurate compass reading and of course trying to do it at night
time its too dark. Where I live is about 1deg west longitude, should I
make allowance for this?. Does this sound feasable or just plain
cobblers ;-)?

Don't do it at noon GMT; do it half-way between sunrise and sunset.
That should be close to local solar noon. Get the times from the paper
or Whitaker's Almanac, and do a rough correction for longitude (4
minutes per degree).

If you want to be over-clever, include yesterday's sunset and tomorrow's
sunrise.


OTOH, if it's worth putting an observatory there you can probably see at
least one distant landmark from a point nearby. Get the direction from
an O.S. map, converting to angle from true north of course, and use that
to determine North from the pier. If you don't hang about, you can use
the sun's rays as a parallel ruler.


OTTH, you need only wait until night and sight on Polaris. It's within
a degree of True North - and if you cannot spot it you've either chosen
the wrong location (sight-lines, weather) or the wrong hobby g. Just
string up a pair of plumb-lines north and south of the pier, adjust
until you can "see" Polaris hidden behind both, turn on a torch, and
felt-top a north-south line in the top of the pier assembly. Do the
rest in daylight.


Or, if you have a perfect horizon and an alarm-clock, determine the
directions of sunrise and sunset, and split the difference (yesterday &
tomorrow as before).


Or, if you have a good sight-line to ground to the North maybe 1-2 km
away and also a GPS : GPS the pier location, send a minion with a flag
and instructions to indicate when at the same longitude and a minute or
two of latitude greater; then sight on him.

--
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Web URL:http://www.merlyn.demon.co.uk/ - FAQqish topics, acronyms & links;
Astro stuff via astron-1.htm, gravity0.htm ; quotings.htm, pascal.htm, etc.
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Many thanks all for the helpful replies. Made me chuckle that John
about the minion with a flag, I mentioned that to `er indoors` and was
told to take a running jump ;-).
Thought I`d try my old trusty Garmin gps 12 to give me a clue also but
turning it on I`d left in some old Duracell `leakproof` batteries that
had leaked (??) and knackered the battery terminal "pah bloody
typical". Anyway estimated my equation of time adjustment from a web
site and its about 4mins so hopefully the azimuth allowance will handle
that.
Knocked up a little desk in there today so all in all coming on nicely.
Clear skies all
Steve

Sun transit was at 11.53 UTC (12.53 BST) here (NW London) today and wil
be at 11.51 at the end of September.

It's at its very earliest (around 11.44) near to Guy Fawkes Day.

I helped my partner do just what you're proposing to do at about 12.13
on a February noontide in 2004...

--
Helen D. Vecht:
Edgware.