POLAR ALIGNMENT OF THE EQUATORIAL TELESCOPE MOUNTING FOR BEGINNERS. (Northern Hemisphere)


 

The most important thing to know before you start...

 


It's easy to set up sufficient for visual observing and it is something that can be done in under a minute with a little practice.  This guide is intended for those wanting to learn how to set up their telescope for simple visual observation.

Having got your new telescope the first thing that will occur to you is that once you have got it together you'll need to know how to set the mounting up correctly.  Many people are put off buying a telescope with an equatorial mounting because they think it's hard to set up.  They think that the more familiar Altitude-Azimuth (Up and Down - Left and Right. Known in astronomy circles as Alt-Az.) will do the job just as well.  This is actually quite untrue.  The Alt-Az mounting is a very difficult mounting to use well with the heavenly bodies.  

 

 

Left:  It looks very complicated I know, but, this diagram attempts to illustrate simply how the move-ments of the heavenly bodies and the Alt-Az mounting's up-down-left-right motions aren't very compatible.
The Equatorial Mounting makes following the objects we see in the sky easy and the simple application of the simple instructions in this guide will see you set up in a very short time. The EQ mounting automatically follows the white lines. This allows you stress-free observation of the wonders of the night sky.   All you have to do is set your mounting up with the correct 'polar alignment'.

 

 Left: Polar alignment?  :o)

 

The principle behind the equatorial mounting is very simple.  

The Earth revolves around its axis every 24 hours.  To compensate for this rotation the mounting has to rotate the telescope around the same angle axis and in the opposite direction at a speed equal to one revolution in 24 hours.

To allow different objects to be seen the telescope mounting has to allow the telescope to move up and down the sky's longitude lines to view different 'latitudes' (Declinations) in a North-South direction.  The mounting therefore has two axes.  The Polar Axis mirroring the Earth's axis and the Declination axis looking from horizon to Zenith and beyond!

 

 

The mounting can be motorised to turn at the same speed as the Earth, or it can have manual controls to effect this rotation called 'Slow Motions'.  Once your mounting has been set up correctly it can follow the heavenly bodies with ease by rotating around the Polar Axis.
 

 

Setting up a "German Type" Mounting. NOT "FORK Type"

< The German Mounting
The set up procedure in this guide is the same for refractors or reflectors and is specific to the 'German Mounting' which is the most common mounting and is the one with the counterweight.  (If your telescope is a Catadioptric Schmidt-Cassegrain then you will probably have a fork mounting with no counterweight and you should Google for your set up technique as this guide will not help you to set up a fork mount! - Sorry).

 

(Image courtesy SkyWatcher Telescopes).

 

Left: :  3" Refractor on German Mounting 
This telescope is in the 'Parked' position - One that is very rarely used for observation (Image courtesy SkyWatcher Telescopes).

Most telescopes are shown in what I call, 'The Parked Position'.  This is purely to illustrate the mounting layout.  You hardly ever use a telescope in this position. (See pictures later!)
To view an equatorial object (M42 in Orion for example):
From the parked position, you would move the eyepiece (Seen bottom right corner) toward our viewing point until the telescope points horizontally, roughly at the top of the fence by the tree, then you would push the eyepiece end downwards (Towards the bottom left corner of the picture) until the telescope is pointing to the top right of this photo and the eyepiece is in the bottom left corner.  The counterweight would not be visible from this point of view, being hidden behind the telescope.  When the scope is pointing due south, the declination axis (With the counterweight) is horizontal.  The polar axis still (and always) points to Polaris.  If this sounds complicated please view the video below  which will explain everything!

 

Preparation: First, roughly set your latitude.

Most mountings have a degree scale on the side to indicate your latitude.  How far North you are of the equator (Your Latitude) is the figure you use to set the angle of the Polar Axis using this scale.

 

It is easy to find your latitude from Google.  For example the English Midlands are 52.5 degrees North.  This means that the first thing to do is roughly set your mounting to your latitude.

You can check this by sighting polaris along the polar axis as show left.

 

 

Next you need to assess the place you intend to set up your telescope for observing.  This ideally should be as far from buildings as possible to avoid the heat rising from the warm buildings affecting the view through the telescope.  You should also have a reasonable view South to get the best out of astronomy.

If you plan to take your telescope out to a remote site to do your observing, then you'll have to set up each time you observe. Getting to know how to set up your mounting is paramount to easy observing.  Try to choose somewhere with a hard area to put your tripod feet.

You need to look at the ground and make sure it is reasonably flat.  If not, you will need to make allowance for any slope when setting up.  For example: If there's a slight slope you will need to set up your tripod legs to take account of this so that your 'mounting head' (The base of the mounting that sits on top of the tripod) is flat.  Some mountings have a plumb-bob or bubble indicator to help ensure this flatness.

 


Setting Up:

 

To fully set up your mount in the correct position you need to have the telescope attached and it needs to be a clear(ish) night!

Locate 'The Plough'.  I am reasonably confident that even the newest amateur astronomer will know the Plough, part of the Great Bear   (Big Dipper in USA) .  Or, if not, then it will be obvious that there are many results on Google that will help you with this.  

 


Locate the Pole Star (Polaris).  This is done by using the 'pointer stars' at the end of the plough, Merak & Dubhe.
(See pic below).  

 

 

You will find Polaris in a reasonably bland part of the sky and once you've found it a couple of times - it's easy!
As the sky rotates nightly, and as the seasons progress you will notice that the Plough (Big Dipper) is found at various positions in the sky. Winter, it's low down in the North, Summer it's high overhead for us in the Northern hemisphere.  This is due to the apparent rotation of the 'celestial sphere'.  The pointers always point to Polaris.  Whether that is up, across, down or slant-ways - They are 'the Pointers', and they point!  :o)

 

 

 

 

 

Left:  The Pointers, pointing!

 

VIDEO Below:  Press 'PLAY>' to see how The Plough moves around the pole with the pointers indicating Polaris.
The position is shown every three hours during a 24 hour period (every 45 degree rotation of the sky).

 

 

You then need to align the polar axis (The one without the counterweight) so it points directly at Polaris, by eye.  Some mountings have a sight which enables this, ( See below if yours does) others do not - Those that do not outnumber those that do by millions! - Either way it is quite easy to squint along the axis and point it at Polaris.  

 

 

Squint: Looking up the Polar axis to line up with Polaris.



This set-up method is sufficient for normal viewing of objects.  

 

You can stop here and start observing...

 

 

 

 

 

 

 

 


That's it:  I've done my best to keep it simple and short!

 

Set-Up and Use Video.

Click the video below to see how this all works out in practice.

 

In use the polar axis continues to point at polaris. IT DOES NOT NEED TO MOVE.  The entire sky is accessible without moving the polar axis.

 


The equatorial mounting is by no means intuitive - You have to learn how it moves.  When I look at eBay listings for telescopes there are many that have obviously been set up to work as an alt-az mount because that's the only thing in our usual experience that makes sense.  The polar axis is horizontal and the declination axis is therefore vertical.  That is the perfect set-up for the equator, by the way.  The Alt-Az mounting is an equatorial on the poles!

 

Above:

This picture shows how some people resort to trying to make this equatorial work as an Alt-Az (Up and Down - Left and Right) mounting.
If you lived in Northern Equador, or Kuala Lumpur it would be properly set up for observation!

However, this telescope was in use in the UK!
By reading this guide I hope you will understand the principle and set up correctly for your latitude.

It is benficial to experiment with your mounting in daylight. 
Start by rotating the telescope on the axis with the counterweight.  This moves the telescope in the north and south (+ & - declinations).
Then rotate about the polar (RA) axis.  This is the motion that follows the movement of the sky.
It's not intuitive by any stretch of the imagination.  In use the telescope very seldom looks like it does when 'parked' and pointing to the pole (As it does in most photos!)
For an excercise in aiming the telescope: Decide on a position in the sky that you'd like to look at and then try to put your telescope in a position that would allow you to view that point.  Then decide on another point.  You'll soon get the idea of how the mounting moves.

 

Once set up the telescope can be carefully pointed to any part of the sky.
Make sure that the telescope is in balance.  That is that the telescope doesn't swing up or down (Move the telescope in it's cradles back and forth to balance this): Make sure the telescope doesn't rotate about the Polar (RA) axis, either telescope heavy or Counterweight heavy (Move the counterweight to balance this movement). You can leave the axis locks slightly engaged to stop the fully free movement of the telescope.

Then, to locate an object, simply loosen off the axis clamps a little so there is only a very slight friction and the telescope will stay wherever it's pointed.

 

 

Other Information:

 

Polaris is actually 3/4 of a degree from the celestial pole, in the direction of the W shaped constellation of Cassiopeia. Or, to put it another way - the celestial pole is 3/4 degrees from Polaris, in the direction of Alkaid, the end star in the handle of the Plough (Big Dipper).

(Polaris Co-ordinates = 2h 40m R.A. +89.25 degrees Dec.)


If your mount has a Polar Axis alignment scope you're laughing!  This is a small sighting telescope that you use to spot Polaris through the Polar Axis of your mount.  The view shows a 1.5 degree circle (3/4 degree x 2) and with a little bit of calculation, (or just twist your star atlas around until the constellations are at the same angle), you can figure out what angle Polaris should be in the sight.  Once this is known you simply put Polaris on the line as shown in the example diagram below, and bingo - You're accurately set up in a few seconds!

 


Make it Easy to Realign in Future!

 

Mark the positions of your tripod's feet.  It is at this point that you could mark the positions of your tripod's feet to help with rough alignment next time.   Particularly if you plan to take your telescope in and out of the house each time, as so many observers have to do.  If you don't have a hard surface (ie you plan to observe on grass) it is wise to put down some small area to set up your telescope on so the feet don't sink into your lawn.  You can opt for three small flagstones, three 8" circles of cement (Garden centre stepping-stones make good bases), one for each foot, set flush with the grass to allow mowing, or making a triangle of angle-iron to spread the weight of the feet.

Mark the feet!   Whether you use flag-stones or circles of cement you can easily mark the correct leg positions not only the position on the flag but the length of each leg if you extend them each time.  Make the marks easy to see as you will have to do this by the light of the moon or a dim red torch!

 

Your 'set up' is now all done.   Once you have done the above stages you can begin observing the sky with your telescope, which will be well enough aligned for visual observation and know that it will be just a few moment's work to set it up in the same position in the future...

For photographic long exposures the mounting has to be aligned much more accurately (and permanently is a good idea!) - The setting up of a telescope like this is well beyond the scope of this simple guide!