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  #21  
Old 30-12-2006, 09:55 AM
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Originally Posted by Dennis View Post
My tripod has a peg on the tripod head which sits over a leg and I set this leg and peg to point True South. I then fit my German Equatorial Mount onto the tripod and using a template that fits on the declination shaft, I adjust the altitude screw on the mount until I am at 27.5 degrees for Brisbane.

The template is a triangular piece of 12mm plywood with the long side of the triangle making an angle of 27.5 degrees to the next longest side. I place the long side against the Dec shaft then place a bubble level on the short side of the triangle and adjust the altitude screw on the mount until the bubble is level. I then know that the Dec axis is at 27.5 degrees even if the tripod head is not level.
G'day Dennis

Don't suppose you'd upload some pics showing this template and how you use it to get the correct altitude for your mount?

Might be a handy little "How To"?

Cheers
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  #22  
Old 30-12-2006, 01:51 PM
Dennis
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Hi Matt

Sure thing. Have a look here where I have just updated a previous post. The post now shows how I can perform a rough polar alignment in azimuth and altitude. Scroll to Msg#16.

Cheers

Dennis
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  #23  
Old 01-01-2007, 09:18 AM
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Phil

This is a photo of the SCP this may help you with the stars around the pole. I have marked Sigma Octans triangle these are the closed naked eye stars to the pole 5th mag. hope this helps.
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  #24  
Old 01-01-2007, 09:44 AM
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If only they appeared so bright (naked eye) from my place, Phil

Last edited by matt; 01-01-2007 at 09:58 AM.
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  #25  
Old 01-01-2007, 09:50 AM
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I get that sort of view from my backyard looking south & SE but when I look north I get a big glow from the city
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  #26  
Old 01-01-2007, 10:05 AM
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I've never seen a sky that dark and clear! There is another way that only requires a clear view of the southern sky. Taking a line through Alpha Crucis and Gamma Crucis, about half the distance to Achernar from gamma Crucis will put you very close to the SCP. A line through Beta Centauri and Achernar about 1/2 way) will also go very close to the SCP, but not quite as close as the first group.
Another method for finding true south is to use a slender shadow cast by the sun as it transits the meridian(not too crash hot in the summer months), but is is workable, all that is then needed is to set the altitude.
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  #27  
Old 02-01-2007, 01:26 PM
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I have another method of alignment.

I bought my Meade 8" SCT on an EQ mount of a retired guy (nice old bloke) who was a bit of a tinkerer, he gave me a pole which i slide into the polar scope hole and it dangles a plumb down towards the ground. At noon EST I point the scope to mag. south, adjust 11 deg. east (Sydney) then move the fine tune nobs so that the shadow of the pole lies along the plumb line.

He says it is then aligned, I mark on the ground the position of the legs and use that in future.

Should I use this method? Does this make sense to you guys? I have not seen this mentioned anywhere else.
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  #28  
Old 02-01-2007, 02:55 PM
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G'day Alex,
that should work ok, except that you might want to deviate from noon a bit to ensure that you align the shadow when the sun is transiting the meridian(not necessarily noon). Today, the Sun transited the Meridian at 1pm DST, wheras on Dec 31st for example, it will transit at 1:10pm DST, so you should check the transit time for each day you want to use this method. Noon (standard time) is just a 'ball park' figure.

Cheers,
Doug
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  #29  
Old 02-01-2007, 04:41 PM
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Hi Alex

Well, yes, but maybe no?

This strange answer is due to how we all synchronise our timepieces using the Standard Time Zones on the Earth. We know the following:

There are 24 hours in a (mean) solar day.
There are 360 degrees in one rotation of the Earth.
Dividing 360 deg by 24 hrs we get 15.
That is, in 1 hour the Earth rotates 15 degrees. This is the equivalent to traversing a Standard Time Zone.
This means that for every 4 minutes of time, the (mean) Sun will appear to move 1 degree in the sky, along the ecliptic.

If you happen to live right on a Time Zone meridian e.g. 150 deg E, then I believe noon will be 12 noon local time (AEST) when the shadows cast by the Sun will be at their smallest. (There is an additional complication called the “Equation of Time” which takes into account the apparent speeding up and slowing down of the Sun in its journey across the sky throughout the year, due to our elliptical orbit around the Sun).

However, as I live in Brisbane at a longitude of 152 deg E, the Sun will arrive at my local meridian at noon local time, some 2 degrees before it would arrive at the 150 deg meridian.

So, noon for me at 152 degrees E would be 11:58am local time (shortest shadows).
Noon for an observer at 150 degrees E would be 12:00am AEST (shortest shadows).
Noon for an observer at 145 degrees E would be 00:20pm local time (shortest shadows).

However, it would be impractical if we had to set our time pieces according to our local time so the politicians deemed that if we live somewhere in the Time Zone centred on 150 deg, we will all follow AEST and not our local time. That is, if we observe or live within ±7.5 degrees of 150 deg E, (142.5 to 157.5 deg E), our timepieces are set to synchronise with the local noon at 150 degrees E.

So, the worst case scenario would be:
At 157.5 deg E, the shortest shadows will be at 11:30am AEST.
At 142.5 deg E, the shortest shadows will be at 00:30pm AEST.

Cheers

Dennis
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  #30  
Old 02-01-2007, 04:52 PM
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Quote:
Originally Posted by paninaro View Post
I have another method of alignment.

I bought my Meade 8" SCT on an EQ mount of a retired guy (nice old bloke) who was a bit of a tinkerer, he gave me a pole which i slide into the polar scope hole and it dangles a plumb down towards the ground. At noon EST I point the scope to mag. south, adjust 11 deg. east (Sydney) then move the fine tune nobs so that the shadow of the pole lies along the plumb line.

He says it is then aligned, I mark on the ground the position of the legs and use that in future.

Should I use this method? Does this make sense to you guys? I have not seen this mentioned anywhere else.
G'Day Alex,

As Doug and Dennis have explained there are problems using this method at noon civilian time... however...

if you download this little clock program I wrote a while ago, you can perfrom your procedure at noon solar time, and you'll be a hell of a lot closer!

http://alsworld.topcities.com/astro/AlsClock.htm

Neat! Mike asked me what the use of solar time was! It's found a purpose!

Al.
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  #31  
Old 02-01-2007, 04:58 PM
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Originally Posted by sheeny View Post
Neat! Mike asked me what the use of solar time was! It's found a purpose!
Al.
…proving yet once more, that Al is a man ahead of his time.

Cheers

Dennis
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