|
Ed,
Finding Celestial True South using Solar Noon Meridian method
Items needed
1 metre length of 12mm timber dowel with a 2mm deep 90 deg cross cut into one end using a hacksaw
2 x 3 metre pieces of 1mm string cotton type
4 x weights like a brick or paver etc...
1 x straight edge, alum angle or ruler 500mm long would be good
1 x fine point black permanent marker
1 x 300mm long Stanley or quality boat type builders bubble level
1 x PC with a planetarium software program. Stellarium is a good choice as it’s free and easy to use
1 x Smartphone like an iPhone
Location
Your observing location ( approximately 1.5 sqm ) or where you will set up your telescope mount should be a reasonably flat and level area with a good view of the sun at around midday ( a paved , tiled or concrete area is preferable) At a remote site you will need to clear the ground and make it reasonably flat or level
Procedure
(Setting up for your Shadow)
Erect timber dowel vertically below your preferred observing tripod position and use the 2 strings to anchors the dowel like tent guy ropes at NSEW using weights to hold it in position. Use your bubble level to ensure dowel is exactly vertical at 90 deg in all directions ( very important ) The hacksaw cuts at the top of the dowel make it easy to adjust the dowel NSEW
Finding Solar Noon Time
(Using your Planetarium like Stellarium )
Start your PC mid morning and open Stellarium. Rotate your cardinal point to the North position and raise view up until you see the Sun
Click on the Sun and then click on the clock , move the time forward or backward to the point where the Suns Alt/Az degrees goes from 359 deg to 0 deg or exactly bisecting the North South meridian line ( refer to top left hand data on screen for Az/ Alt deg )
Record this exact time which is Solar Noon ( eg 12.35pm )
(Finding Solar Noon on a Website)
Most meteorological websites show Solar Noon times at or near your observing location
Marking your Celestial True South Line
Go to your observing location 10 minutes before Solar noon with your smartphone , ruler and permanent marker. The dowel should be casting a 12mm wide +500mm long shadow on the surface towards the south
At exactly Solar Noon time mark a thin line on the surface or ground from the base of the dowel outwards along the exact centre of the shadow for at least 500mm ( be as precise as you can )
This line is marks the Celestial Meridian (True North / South )
Use this line to align your tripod front leg to True South and then set up your mount
I found this method far more accurate than any app or compass with magnetic declination
Cheers
Martin
|