Altaz Go-To mounts are a handy option for busy astronomers as they enable you to slew your scope to thousands of celestial objects at the touch of a button.
To make the most of this convenience, however, these mounts need to be set up carefully and methodically.
This guide will help you get your routine down to a tee so you can get out observing quickly and with the minimum of effort.
For the purposes of this article, we’re using a Sky-Watcher Skymax-127 loaned to us by The Widescreen Centre.
What you’ll need to get started
Compass and inclinometer – If you can’t see Polaris, use a good compass and an inclinometer to find the celestial pole. Your local latitude is the celestial pole’s altitude.
Spirit level – This is useful for levelling the tripod if it doesn’t have one already built in. Some mounts also need the scope to be levelled prior to alignment.
Power supply – A rechargeable 12V battery is a much more reliable alternative to alkali batteries.
Star chart – Use your preferred star chart or planisphere to find suitable alignment stars.
Eyepieces – You will need low- and high-power (at least 100x) eyepieces to centre your alignment stars, and a medium-power eyepiece to confirm that alignment is successful.
The first thing is to choose a site for your telescope.
There are several factors you might what to consider when making this decision: low horizons (particularly to the south), lack of direct light pollution, firm ground and shelter from the wind are all advantages worth keeping in mind.
Once you have settled on a location, use a compass to work out which direction is north and determine your local longitude and latitude – you can find this information online at www.latlong.net.
Place your tripod on the ground and make it as stable as possible.
Set the tripod’s height carefully as you will lose alignment if you have to alter it later on, adjusting each leg individually to make sure it is level.
Many tripods are fitted with spirit levels to help you to do this; if yours doesn’t have one, rest an external spirit level on the accessory tray.
To save time in the future, you can mark the ground where the tripod legs stand.
For a grass surface, brightly coloured plastic golf tees make good temporary markers, or for a longer-term marker you could cut out the turf and put in a small paving slab.
On hard surfaces you could apply a spot of paint or even drill a small depression into which the tripod feet can settle.
It’s a good idea to have one leg pointing north – this will be useful if you decide to upgrade to an equatorial mount at some point in the future.
Another time-saving trick for setting height and levelling is to mark the position of the lower sections of the tripod legs with a marker or stickers.
Mount alignment routines vary between manufacturers, so read the instructions carefully for your particular mount.
On some mounts you need to orientate the scope horizontally or point it towards the celestial pole (aim at Polaris) before you switch it on.
If the mount is fitted with setting circles, you can use these, but they might not be very accurate.
To avoid mechanical sag affecting the accuracy, make sure all the thumbscrews on the tripod, mount and telescope tube are tightened properly.
Data is critical
Once you’ve switched on the mount, you will need to input the latitude, longitude, date and time.
Take care to enter these correctly; note that on many mounts the date format is MM/DD/YYYY.
Also be aware that you will need to activate daylight saving time when the clocks change in spring.
Check which alignment methods are available on your mount.
Three-star alignment takes a little longer than two-star, but you will enjoy more accurate slewing.
The farther apart the alignment stars, the more accurate the alignment will be, so choose stars at least 60° apart: one each in the east, west and (for three-star alignment) south.
Centre the first alignment star in the view through your finderscope; you’ll need to make sure your finder is well aligned to your telescope tube in advance.
Once done, centre the star in a low-magnification eyepiece.
Swap the low-power eyepiece for a high-power one and do the same again, then confirm the position on the handset.
Once the first alignment point has been established, the mount usually slews to the next chosen star.
When the last star has been centred and confirmed, you will hopefully see an ‘alignment successful’ message.
If not, you will have to go through alignment again.
Assuming it is successful, pick an object, preferably not too close to any of the alignment stars, and watch how accurately the mount slews: your new target should be within the field of view of a medium-power eyepiece.
Some mounts have a feature called ‘pointing accuracy enhancement’, which can be used for fine tuning if your target is still a little off-centre.
When you’ve chosen a suitable site for your telescope, get your bearings.
Locate north and look up the local latitude and longitude to one arcminute.
Prepare everything else you will need for your observing session, plus a spirit level, star chart and the mount’s manual.
Place your tripod at the observing site with one leg facing north, then set the tripod height and level it.
Make sure the ground is firm and that all the tripod fixings are tight.
If you are going to use this site regularly, mark the tripod leg positions to for next time.
Attach your observing telescope to the mount, plug in the Go-To hand controller and connect the power supply.
Consult your mount’s manual to check if the scope needs to be pointed in a particular direction before you turn on the power.
The mount will now prompt you to enter various details. Set the date, time, time zone and local coordinates.
These need to be accurate so that the mount can correctly plot the planets and your local horizon.
Press enter to proceed to alignment.
When alignment is complete, slew to a new target and check that the mount centres it in a medium-power eyepiece.
If your target is outside the field of view, repeat steps 5.
‘Pointing accuracy enhancement’ can be used for fine tuning, if your mount supports it.
Andrew Phethean is a keen astronomer
This ‘How to’ originally appeared in the February 2014 issue of BBC Sky at Night Magazine.