Magnetic or True South for Pier?

[MattT]

I'm about to build a 1.5m high Pier out of old red house bricks. My back fence faces magnetic South. Mount is my ATM 2" Pillow Block which will have AZ adjust on it. 11º East is where I need to face it, roughly and I wonder if a degree scale engraved on the Az part would be easy to get close to the pole...and then the Pier would be in line with the fence not at a slight angle...maybe I'm over thinking this?
Thoughts....

Matt

[Wavytone]

Use the stars.

Can you borrow an Equatorial mount with a decent dec circle, or encoders ?

If so use that... Choosing a bright star near the east or west horizon and use an Astro program to find its declination; lock the dec axis to the stars declination, then adjust azimuth of the mount so you can centre the star in a finder or small scope; this will get you within a fraction of a degree of the dec circle is accurate. This works best for stars with dec between +15 ... -15 degrees.

Once you have the az right set the dev axis horizontal and rotate the scope down to point at your fence (the scope should be pointing due south on one side of the mount) Put a mark on the fence. Flip the scope to the other side of the mount and repeat. These marks provide a ready guide to where south is.

Now plonk the pillow block mount on the pier and align with the marks on the fence.

To set the altitude use a star near the meridian: use any Astro program to show which stars are on the meridian, or use any smartphone app that provides a clinometer.

[skysurfer]

Originally Posted by Wavytone

...or use any smartphone app that provides a clinometer.

This won't work, too inaccurate. Go to a building supply shop or even ebay. These devices work to 0.1 degrees accurate.
I have a Toolcraft one, got for $35.

For adjusting the Mount, use True south, not magnetic south.

[ZeroID (Brent)]

Solar noon is the easy way to go for a Nth/Sth line.
Get a plumb bob, string, weight. hang it so the shadow at solar noon falls across your intended pier site. Mark the shadow nth and sth. T-Square if for east\west ( 3.4.5 Rt angle triangle )

http://www.esrl.noaa.gov/gmd/grad/solcalc/

Calculator link above. SN is normally about 20 past clock noon.
Refine it with drift alignment when you build the pier and add the mount.

Use your simple phone clinometer to get close to the right Dec angle, then PHD2 has a process. Mine was surprisingly close, just make sure it's a straight edge where they meet.

[MattT]

A picture is worth a thousand words...this is a square pier with a square EQ head on it. I have 2 EQ mounts so I have no trouble finding the pole, my question was more along the lines of should the pier face the SGP or magnetic south. I'll build it so it faces the SGP not magnetic south.

The clinometer app I use is accurate enough. I have used Solar noon to find true south, as well as the length of wood on the ground with a compass as described by Trevor Hand...that works too.

Cheers

[alocky (Andrew lockwood)]

As long as you've got enough azimuth adjustment to accomodate the magnetic declination it makes no practical difference, and I'd be inclined to align the pier with the fence - otherwise significant other will tell you it's crooked.
Turning on my pedant mode you will want to align your mount with the south celestial pole, not the south galactic pole. This will improve tracking considerably. Pedant mode off.
Cheers,
Andrew

[MattT]

If only I could type good....yeah SCP....SGP shheeees. My wife already thinks I'm nuts. Several years ago I planted a Cypress Hedge in front of the fence so I hope a crooked pile of bricks will pass the quality control test....

[alocky (Andrew lockwood)]

Originally Posted by MattT

If only I could type good....yeah SCP....SGP shheeees. My wife already thinks I'm nuts. Several years ago I planted a Cypress Hedge in front of the fence so I hope a crooked pile of bricks will pass the quality control test....

Well it's worth clarifying as one moves and the other doesn't.
If it's not going to bug anyone then why not go true Sth. In my case, the pier is 1.5m square, sticks up 4m into the second floor observatory, is near the pool and a couple of walls of the house, which are about 20 degrees off nth, so there was no question about it. But here in wa the magnetic declination is only 30 arc minutes anyway.
Cheers,
Andrew