Polar Alignment

Polar Alignment

By Steven Mohr

There are many excellent articles on how to configure your equatorial mount to achieve an exact polar alignment, and some can be found here:

My Astro Shop: Quick Polar Alignment Guide: Quick guide to performing a Southern Hemisphere polar alignment.

Basics of Drift Alignment / Polar Alignment: a good guide to start you off to achieving an accurate alignment of your mount.

Astro Baby’s Guide to setting up an EQ5 (EQ6): Use this guide to set up your mount, and to understand different aspects of the mount.

This article is for beginners to supplement these other articles to achieve an accurate polar alignment for the Southern Hemisphere.

To perform a polar alignment, the below pieces of information may not be easily found by the beginner (note this is information is intended for Australian Astronomers):

  1. Your Longitude: Used for:
    • To establish your “magnetic field component”, see item 4 below,
    • Alignment of mount: not used specifically for this purpose.
  2. Your Latitude: Used for:
    • To establish your “magnetic field component”, see item 4 below,
    • Alignment of mount: To align the angle (declination) of your mount to the celestial pole

View of the EQ Mount Latitude Setting

Screen capture from Starry Night showing information required to set your actual viewing location.
  1. Your Altitude (not so important), used to:
    • To establish your “magnetic field component”, see below,
    • Alignment of mount: not used specifically for this purpose
  2. Your magnetic field component (the offset to the magnetic South position): Used for:
    • Alignment of mount: To point your telescope in the correct direction (azimuth) to the celestial pole

I like pictures to explain things to me, so I’ll try to use as many as I can to make this as easy as possible.

Now normally, the items above are left to the reader to find out, and I suppose items “1” to “3” are quite simple to work out with internet resources like Google Earth and the like, but I will show you another resource for Australian astronomers, that will also include item “4” (the magical number to making the alignment work, especially when you haven’t got a polar scope).

In regard to these items, have a look to the Australian Government site, Earth Monitoring > Geomagnetism:


Go to the page, Home > Earth Monitoring > Geomagnetism > Geomagnetism Data & Reports > AGRF Calculations:


Here you will have the following page:

All the answers to Items 1 through to 4 will be found right here!

The purpose of this form, is to find your item “4. Your magnetic field component”, but in working this out we must first find your geographical location information.

Look to the top of this page for the text:

“If Location coordinates are unknown, try the place name search.”
Click on the place name search, to take you to the following page:


From what I have found, not all locations are listed, but major cities are easy to find, so let’s try using “Melbourne” as the example for this case (see above the inputted information for Melbourne).

To start the search, click the Submit Query button.

The result will be as follows:

Now click on the location: Melbourne, and the following page will be generated:

From the above, you now have the latitude and longitude for Melbourne, and you can now enter this information into the below page to get your Item “4. Your magnetic field component”:

Home > Earth Monitoring > Geomagnetism > Geomagnetism Data & Reports > AGRF Calculations:


Once you put your information in, press Submit Request to proceed. Remember to use a minus sign at the Latitude field for degrees to indicate the request is for the Southern Hemisphere.

The resulting page is as follows:

In summary, from the above information, your location information for Melbourne is as follows:

  1. Your Latitude: -37 degrees, 49 minutes (NOTE: the minus sign is for the Southern Hemisphere)
  2. Your Longitude: 144 degrees, 53 minutes.
  3. Your Altitude (not so important): leave at 0.
  4. Your magnetic field component: 11.464 deg (Important!)

OKAY! Now you can start to use this information to set up our mount!

The last thing I’ll include in this guide, is how to use Item 4 in relation to using your compass.

Take note of your magnetic field component, and in the examples case above for Melbourne, it was 11.464 deg (or 11.5 to keep it simple).

Look at your compass, and it should have a rotating dial to compensate for this magnetic field component. To adjust for this amount, you will need to rotate the dial clockwise by 11.5 points, see below for example:

Here is your starting position with the compass aligned to the South:

Note: Compass held in opposite direction to North, white end points to South, but holding the compass to utilise the North alignment arrow underneath

Next rotate the compass clockwise for the positive adjustment number 11.5, as indicated below:

Now you are ready to use the compass for a Melbourne location. Just align the magnetic pointer to be in line with the indicator, and then place the straight edge of the compass in line with the direction of your mount to get the correct direction towards the Southern Celestial Pole.

If you have a negative variance, you must adjust the compass anti-clockwise.
Hope this information helps! Good luck.