Melbourne true south

[Moon (James)]

This could end up being the most confusing thread ever on IIS the way it's going!

1+ vote for the solar noon method.

James

[rcheshire (Rowland)]

Point Compass 180 Magnetic, then add 11 degrees - this is True South

Variation East Magnetic Least - add to get true. Magnetic is less than true with east variation.

[toc (Tim)]

Another method is to setup a camera behind your telescope and night, and do some star trails for a few hours

[tuc_47 (Del)]

For what it's worth
a) The declination (+12-59) at Traralgon is about 1.5 deg different from Melbourne (+11-33) [http://www.magnetic-declination.com/]
b) The declination for Rockingham is close to -2 degrees
c) Solar noon is only correct 4 times a year [http://www.ips.gov.au/Category/Educa...tionOfTime.pdf ] (up to 16 minutes or 4 degrees : mid-Feb and late Oct)
d) the "star trail" idea is not bad!

My suggestion: Look at your property title and it will show the true bearings of your boundaries. Get some string and use simple trig to lay out a reference line in your garden.
OR - visually locate Achernar and Beta-Centauri and split the difference.

[adman (Adam)]

I think that graph refers to mean solar noon only being correct 4 times a year - ie actual solar noon (when the sun crosses the meridian) only occurs at 12:00 4 times a year.

Solar noon calculators on the web take this into account and give you actual solar noon for your lat/long.

In any case you only need to be accurate with your initial mount setup with 5 or so degrees either side of true south - the final bit you get with drift alignment or whatever other method you use to refine you alignment.

Adam

Originally Posted by tuc_47

For what it's worth
a) The declination (+12-59) at Traralgon is about 1.5 deg different from Melbourne (+11-33) [http://www.magnetic-declination.com/]
b) The declination for Rockingham is close to -2 degrees
c) Solar noon is only correct 4 times a year [http://www.ips.gov.au/Category/Educa...tionOfTime.pdf ] (16 minutes is 4 degrees)
d) the "star trail" idea is not bad!

My suggestion: Look at your property title and it will show the true bearings of your boundaries. Get some string and use simple trig to lay out a reference line in your garden.
OR - visually locate Achernar and Beta-Centauri and split the difference.

[rcheshire (Rowland)]

My suggestion: Look at your property title and it will show the true bearings of your boundaries. Get some string and use simple trig to lay out a reference line in your garden.

Did the same - works very well.

[ColinS (Colin)]

Many thanks all fro your assistance. I must admit that it is very confusing. Jandakot Airport (which I just looked at) says 3.78 degrees. Am I reading all the you have all told me wrong, is the declination fro Rockingham 2, 4 or 11 degrees. I must be slow.

[mithrandir (Andrew)]

Originally Posted by ColinS

Many thanks all fro your assistance. I must admit that it is very confusing. Jandakot Airport (which I just looked at) says 3.78 degrees. Am I reading all the you have all told me wrong, is the declination fro Rockingham 2, 4 or 11 degrees. I must be slow.

Where did you look? AGRF says -1.685 deg

[ColinS (Colin)]

Hi Andrew,
I used the site of AGRF. I put in Lat: 32,16,47 S, and Long: 115,45,45 E and it threw up 4.635.
When I went to Jandakot Airport (cand find the address again right now) it gave 2 degrees.

[mithrandir (Andrew)]

Originally Posted by ColinS

Hi Andrew,
I used the site of AGRF. I put in Lat: 32,16,47 S, and Long: 115,45,45 E and it threw up 4.635.
When I went to Jandakot Airport (cand find the address again right now) it gave 2 degrees.

Are you sure you didn't misread -1.6 as 4.6?

If you look at the image linked from the AGRF page you'll see the lines of equal declination around Perth run more or less NW to SE. Your position is roughly 18.5Km SW of Jandakot so a slight difference is to be expected.

Your coords:
Requested: Latitude -32o 16' 47", Longitude 115o 45' 45", Elevation 0 km, Date 2011/01/1
Calculated: Latitude -32.2797o, Longitude +115.7625o, Elevation 0.00 km, Epoch 2011.0000
Magnetic Field Components
D = -1.816 deg

The place names data for Jandakot:
NAME STATE FEATURE CODE STATUS LAT (DD MM) LONG (DD MM) ELEVATION (m)
JANDAKOT AIRPORT WA AF (Airfields) Official -32 06 115 52 -

Requested: Latitude -32o 6' 0", Longitude 115o 52' 0", Elevation 0 km, Date 2011/01/1
Calculated: Latitude -32.1000o, Longitude +115.8667o, Elevation 0.00 km, Epoch 2011.0000
Magnetic Field Components
D = -1.685 deg

To see how a little change can affect the value, Google Earth puts Jandakot at 32:05:53S 115:52:49E and that changes the declination to -1.678 deg

For you purposes the differences are irrelevant.

Andrew