Polar alignment is a process of aligning the axis of an equatorial mount with the south celestial pole (SCP), which is the point in the sky that all the stars appear to rotate around. Polar alignment is essential for astrophotography, as it allows the mount to track the motion of the stars and keep them within the field of view.
However, polar alignment can be challenging for observers in the southern hemisphere, as there is no bright star near the SCP like Polaris in the northern hemisphere.
Here are some simple tools and techniques you can use to help you polar align your tracking mount.
What you need
To polar align your tracking mount in the southern hemisphere, you will need the following items:
A smartphone with an app that can show you the position of the SCP, such as PS Align Pro (iOS), PolarAligner Pro (Android), or PhotoPills. Or software with a built-in polar alignment routine, such as Sharpcap, N.I.N.A or Astrophotography tools.
A polar alignment adapter that can attach your smartphone to your mount’s dovetail or screw. You can order one online or make your own using a piece of wood and some silicone stickers.
A spirit level to make sure your mount is level.
A compass to find south.
A latitude calculator to find your current latitude, such as mygeoposition.com, whatsmygps.com or LatLong.net.
Step 1: Set up your mount
The first step is to set up your mount on a flat and stable surface. Use the spirit level to make sure your mount is level. Then, use the compass to point your mount towards south. You can also use a landmark or a star map to find south, but make sure it is accurate.
Next, you need to adjust the latitude of your mount. The latitude is the angle between the horizontal plane and the axis of your mount. To find your current latitude, you can use an online calculator or a GPS device and enter your location. For example, if you are in Brisbane, Australia, your latitude is about -27 degrees.
To adjust the latitude of your mount, you need to locate the latitude adjustment knob and nut on your mount. Loosen the knob and turn the nut until the pointer matches your latitude. Then, tighten the knob to secure it.
Refer to What's a German Equatorial Mount for images to help you locate the adjustment knobs.
Step 2: Balance your scope
The second step is to balance your scope on your mount. This will ensure that your scope does not drift or strain your mount’s motors. To balance your scope, you need to locate the setting circles on your mount. These are two dials that show the right ascension (RA) and declination (DEC) of your scope.
To balance the RA axis, unlock the RA clutch and release the screw on the counterweight. Then, move your scope until it is parallel to the ground. Adjust the position of the counterweight until your scope stays balanced without any support. Then, tighten the screw and lock the RA clutch.
To balance the DEC axis, unlock the DEC clutch and move your scope until it is perpendicular to the ground. Adjust the position of your scope until it stays balanced without any support. Then, lock the DEC clutch.
Step 3: Polar align your mount
The final step is to polar align your mount. There are a couple of different methods you can use such as drift alignment, a mobile phone app, software or the built-in star alignment on your mount's hand controller.
Alignment via software
Astrophotographers using dedicated astrophotography cameras can use the polar alignment routine within certain acquisition software, such as Sharpcap Pro, N.I.N.A or Astrophotography tools. These software applications use a series of plate-solved images to ascertain the direction your telescope is pointing.
Using an adapter and polar alignment app on your mobile phone
If you are a visual observer or astrophotographer using a digital camera can use a smartphone and polar alignment adapter.
To do this, you need to attach your smartphone to your mount using the adapter. Make sure your smartphone is secure and flat on the adapter. Then, open your app and select the polar alignment mode. The app will show you a live view of the sky with an indicator of where the SCP is. You need to align this indicator with the centre of your smartphone’s screen.
The drift method
Drift alignment is a method of polar alignment that uses the declination drift of a star to adjust the azimuth and altitude of the mount’s polar axis. Drift alignment is more accurate than using a polar scope or a compass, but it requires more time and patience. Here are some steps to drift alignment:
First, you need to do a rough polar alignment using a polar scope, a compass, or a landmark. This will make the drift alignment easier and faster.
Next, you need to balance your scope on your mount using the setting circles and the counterweight. This will prevent any unwanted movement of your scope due to gravity.
Then, you need to attach an eyepiece with illuminated crosshairs or reticle to your scope. This will help you monitor the drift of the star in your field of view. Note: You can use a digital camera or a dedicated astrophotography camera too.
After that, you need to choose a reference star near the celestial equator and within an hour of the meridian. The meridian is the imaginary line that divides the sky into east and west halves. You can use an app or a star map to find a suitable star.
Next, you need to centre the star on the crosshairs and let it track for about five minutes without making any corrections. You need to ignore any drift in the east-west direction, as that is due to the periodic error of your mount. You only need to focus on the north-south drift, as that indicates misalignment in your polar axis.
If the star drifts north, it means your mount is pointing west of south. You need to adjust the azimuth knob on your mount to move it slightly eastward. If the star drifts south, it means your mount is pointing east of south. You need to adjust the azimuth knob on your mount to move it slightly westward.
After making a small azimuth correction, you need to recenter the star on the crosshairs and wait another five minutes. You need to repeat this process until there is no noticeable north-south drift.
Once you have aligned your mount in azimuth, you need to repeat the same process for altitude. You need to choose a reference star near the eastern or western horizon and within 15 degrees of the celestial equator. You need to centre the star on the crosshairs and let it track for about five minutes without making any corrections. You need to ignore any drift in the north-south direction, as that is due to atmospheric refraction. You only need to focus on the east-west drift, as that indicates misalignment in your polar axis.
If the star drifts east, it means your mount is pointing too high. You need to adjust the altitude knob on your mount to lower it slightly. If the star drifts west, it means your mount is pointing too low. You need to adjust the altitude knob on your mount to raise it slightly.
After making a small altitude correction, you need to recenter the star on the crosshairs and wait another five minutes. You need to repeat this process until there is no noticeable east-west drift.
You have now completed drift alignment for your tracking mount. You can remove your eyepiece and attach your camera or eyepiece. You can also use software such as PHD21, SharpCap2, or Ekos3 to assist you with drift alignment if you prefer.
Using your hand controller
Star Alignment via your hand controller
One of the methods to polar align your mount using a hand controller is the three-point star alignment method. This method uses three stars near the meridian, the imaginary line that divides the sky into east and west halves, to calculate the amount of error in your polar axis and correct it. Here are some steps to perform this method:
First, you need to do a rough polar alignment using a polar scope, a compass, or a landmark. This will make the three-point star alignment easier and faster.
Next, you need to balance your scope on your mount using the setting circles and the counterweight. This will prevent any unwanted movement of your scope due to gravity.
Then, you need to power on your mount and hand controller and enter the date, time, and location information. This will help your mount locate the stars in the sky.
After that, you need to select the three-point star alignment option on your hand controller. This is usually under 'Utilities". The hand controller may suggest a guide star for you near the meridian. You can accept this or choose a different star if you prefer.
Next, you need to centre the guide star on your eyepiece or camera using the arrow buttons on your hand controller. Then, press enter to confirm. The hand controller will then suggest another guide star for you near the meridian and on the opposite side of the sky. You need to repeat the same process of centring and confirming this star.
Finally, the hand controller will suggest a third guide star for you near the meridian and close to the zenith, which is the point directly above your head. You need to centre and confirm this star as well. The hand controller will then calculate the amount of error in your polar axis and display it on the screen. It will also tell you how to adjust your mount’s azimuth and altitude knobs to correct this error.
Once you have made the adjustments, you have completed the three-point star alignment method for polar alignment. You can now proceed with your observing or imaging session.
Making adjustments using the azimuth and altitude knobs
To align your mount with the SCP, you need to adjust the azimuth and altitude knobs. The azimuth knob controls the horizontal movement of your mount, while the altitude knob controls the vertical movement.
Loosen both knobs slightly and move them until the SCP indicator is centred on your screen. You may need to switch between knobs several times to fine-tune your alignment. When you are satisfied with your alignment, tighten both knobs firmly.
You have now completed polar alignment. You can remove your smartphone and adapter from your mount and attach your camera or eyepiece.
If you are using a goto equatorial mount you can now proceed to platesolving to fine-tune your goto accuracy.
Congratulations! You are now ready to enjoy astrophotography or stargazing with your tracking mount in the southern hemisphere.
If you have any questions or feedback, please leave a comment below or contact me.
Clear skies!
Cover image supplied by Vecteezy.
Comments