Setting Latitude

[alandee]

hi folks,
Just a quick one .. Please someone confirm that if I'm at 35 deg Lat and I want to set up my wedge, the northern hemisphere scale on the wedge reads 55 ? I've currently set the dec scale on my scope to 90 when pointing straight up in alt/az.
My understanding is I then lower it by my latitude ( 90-35 = reads 55 ) lock it, then mount it on my wedge, whack a torpedo level on the cover and adjust the wedge until the level is erm level :) .. am I doing this right ? Should the wedge actually read 35 deg ? or is it a northern / southern pole trap for young players ? I've cut a template at 35 degrees using a protractor and it confirms my suspiscions, and it would explain why after a half dozen nights i've gotten nowhere drift aligning :doh:.

because we are in the - 90 south it kinda makes sense.

Thanks in advance

[Dennis]

Hi Al

When I lived in the UK, I set my Vixen latitude scale to 54 degrees, the Latitude of Leeds.
When I moved to Brisbane, I set it to 27.5 degrees, the Latitude of Brisbane.

This is simply an angular measurement of the inclination of the axis of the Earth's rotation, which corresponds to your Latitude.

As I have never used a Meade wedge, I cannot comment on its Latitude scale, but I would be surprised if it is not just as straightforward as the Vixen's. That is, it doesn't care whether its N or S of the equator.

Cheers

Dennis

[Dennis]

Hi Al

I’ve just added a quick and dirty diagram which shows the following:

Earth rotates about its N – S axis of rotation.
The Equator is at right angles to the axis of rotation.
Brisbane is at Latitude 27.5 deg South.
As I stand in my back garden, the plane of my Horizon stretches out.
My Horizon plane is at right angles to the imaginary line joining Brisbane with the centre of the Earth.
The SCP appears to lie on an imaginary line 27.5 degrees above my Horizon due to the geometry of a line intersecting two parallel lines.

Hope that makes it clearer?

Cheers

Dennis

[mick pinner]

whatever your latitude is subtract it from 90 and that is the setting on your wedge.

[Dennis]

Mick

Does the Meade wedge scale run from Zenith to Horizon?

The Vixen runs from Horizon (0 deg) to Zenith (90 deg), hence for Brissie you set 27.5 deg.

Thanks

Dennis

[mick pinner]

regardless of how your wedge latitude scale reads, in the southern hemisphere your latitude is set by deducting your latitude from 90 degrees not by adding to zero degrees that is why southern hemisphere latitudes are sometimes specified as minus degrees. My latitude is -38 or 38 degrees south therefore my wedge is set to 52 degrees.

[alandee]

Thanks Dennis, appreciate the efforts, I think I've got the concept 'right' in my twisted little mind, it was more the actual implementation that has had me guessing. Your mount makes a lot more sence!

A clear head, a day off work, no soccer last night and a pot of coffee and I'm thinking that Mick has confimed my suspiscions ! The nail in coffin was the 35 degree template I drew up didn't match by any stretch of the imagination to my wedge set at 35 degrees.

:cheers: If I ever find myself in Monbulk I owe you a beer at the local.

al

[Dennis]

Ahh, the penny has now dropped!

So, the forks on a fork mounted SCT represent the polar axis of a German Equatorial Mount. Setting the wedge to 90-38 would then ensure the forks are pointing to the SCP and it’s the forks that would make an angle of 38 to the horizon, not the base of the mount.

Good pick up Mick and thanks for the clarification.

Cheers

Dennis

[mick pinner]

When your latitude is set to the correct mark and your tube is set to 90 degrees in Dec then your scope will be pointing pretty much directly to the SCP and from then a drift alignment will be needed to get spot on.

[alandee]

It will be nice trying to drift align without being 20 degrees off to start with ! ;)