Melbourne true south

[PeterO]

Hi all,

Does anyone know the deviation between magnetic south and true south for Melbourne/Latrobe Valley area.

Cheers Peter.

[turbo_pascale]

It's 11 degrees.

I'm not on my ususal PC, but there are websites (I think the USGS (US Geological Survey) website) that you can plug in lat/long and get the figure.

[PeterO]

Thanks very much Turbo.

Peter

[OneOfOne]

That's 11 degrees to the East, or to your left when facing south.

[acropolite]

Finding true south magnetically can be influenced by anything magnetic nearby. An alternate method is to use a vertical stick at solar noon and note the direction of the shadow as per this post. (http://www.iceinspace.com.au/forum/showthread.php?t=5690&highlight=solar+noon)

[Karlsson]

The easiest and probably most accurate way is here: http://www.ga.gov.au/oracle/geomag/agrfform.jsp

:)

[astro_nutt]

I set mine for 11.5 which when using a convertor (EQ to Alt-Az) most object are within the finderscope FOV.
Cheers!

[AstralTraveller]

Magnetic north is east of true north. So when facing south magnetic south is to the right of true south. You can buy compasses which allow you to adjust this offset (it's called magnetic declination) in the compass so you just point the compass to south.

[ColinS]

I am new to this and it dont seem so easy.
I live in Rockingham W.A. and want to find true south. I have been to the Government site shown above and it gives me a reading of -4.634, however, someone else told me that I should point my compass due magnetic south and then the true south would be 12 degrees to the east of that. If the declination says -4.634, is that the difference, or 12 degrees. Is the -4.634 degrees or some other measurement.

[Auster1b]

Colin, my Aeronautical Chart shows 2 degrees west, the same as the current listing for Jandakot.
Neil.

[mithrandir]

Try here:
http://www.ga.gov.au/oracle/geomag/agrfform.jsp

If a ball park value is enough use the declination images at the tag:
http://www.ga.gov.au/oracle/geomag/agrfform.jsp#2005images

[adman]

Really - the shadow method at solar noon is the easiest. You only have to get it within 5 degrees or so as the adjustment on your mount will cover that much when you are drift aligning.

Use a plumb-bob with a thick-ish string and you won't need a stick in the ground

[GrampianStars]

No No No my friend :screwy:
For East magnetic variation
Thats WEST (to your right) when facing south! :thumbsup:

[mithrandir]

Place Names Search Results
NAME STATE FEATURE CODE STATUS LAT (DD MM) LONG (DD MM) ELEVATION (m)
ROCKINGHAM WA LOCB (Towns & Localities) Official -32 16 115 43 -

Australian Geomagnetic Reference Field Computation

Requested: Latitude -32o 16' 00", Longitude 115o 43' 00", Elevation 0 km, Date 2011/01/1
Calculated: Latitude -32.2667o, Longitude +115.7167o, Elevation 0.00 km, Epoch 2011.0000

Magnetic Field Components

D = -1.833 deg

Therefore your accurate, compensated magnetic compass will be pointing about 1.8 deg west of true north. Equally 1.8 deg east of true south. That should be within the azimuth adjustment range of any GEM if you were to start with the mount aligned on magnetic south.

If your tripod is steel or there is any steel fences/reinforcing/tanks/etc nearby, it will affect your compass.

Andrew

[GrampianStars]

G'Day Colin
Magnetic variation is WEST for your location
So When facing South point Scope EAST
by the variation in degrees :thumbsup:

same as Andrew's calculation
Magnetic Field Components D = -1.833 deg

[GeoffW1]

Hi,

When you read the post, he could have meant that, could he not?

Cheers

[rcheshire]

Confused? Variation East Magnetic Least, Variation West Magnetic Best. Basic Nav.

http://www.free-online-private-pilot-ground-school.com/navigation-basics.html

Down the page a bit. Isogonals in this region intersect Longitude E - W, roughly SW direction.

[Kris]

Simply, your compass will show that South is 180 degrees (Magnetic). If you live in Melbourne your magnetic declination is 11.18 degrees to the East. That means your True South on your compass will be 168.82 degrees.

:-)

[OICURMT]

Submitted for IIS Reference.

http://www.ga.gov.au/servlet/BigObjFileManager?bigobjid=GA16056

[Zaps]

This is a useful site:

http://www.solar-noon.com/

[Moon]

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]

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]

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

[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/Educational/The%20Sun%20and%20Solar%20Activity/General%20Info/EquationOfTime.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]

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

[rcheshire]

Did the same - works very well.

[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.

[mithrandir]

Where did you look? AGRF says -1.685 deg

[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.

[mithrandir]

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