Check your compasses

[astroron]

A very interesting event is soon to happen at
the Royal Greenwich Observatory.
It would be cool to be there when it happens.
https://www.sciencealert.com/compasses-are-about-to-do-something-that-hasn-t-happened-in-over-300-years?utm_source
Cheers:thumbsup:

[Wavytone]

Aargh they perpetuated the use of the misnomer "magnetic declination" when its correct term is "magnetic variance".

What is interesting is to see it varied by 25 degrees through the 18th century - more than enough to cause real issues with navigation using a map and compass.

[willilamwgn]

Does this mean that when we set telescope using a magnetic compass it should point exactly as the magnetic south?

[Dennis]

Hi William

I am not sure how up to date this is:

http://www.magnetic-declination.com/Australia/Sydney/124736.html

But it still shows +12deg 37min for Sydney.

Cheers

Dennis

[Sunfish]

Better still , you can go here and get a magnetic variation for any place at any time in the past. Handy if you have some old survey information in magnetic coordinates.

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

[willilamwgn]

Thanks Dennis and Ray, for providing the link to the reference sites.

[Wavytone]

Only at Greenwich, or nearby (ie most of uk), as the magnetic pole is at 0 longitude. But it’s not at latitude +90 so elsewhere it has a non zero variance. To make matters complicated the magnetic field lines are neither straight nor circular so modelling it mathematically is not trivial.