GOTO Mounts - A Modern Revolution
One of the major reasons that amateur astronomy has seen a recent revolution in popularity, is the accessibility of an aspect of astronomy previously considered difficult or complicated. For beginners, it can seem a long daunting exercise finding their way around the sky and identifying where amongst the confusing array of bright dots, all the interesting deep-sky objects and colourful double stars are, and which of the brighter stars, if any, are actually planets. In the decades before computerised telescopes, observing was all about manual telescopes being pushed around the sky from one object to another, or searching for "faint fuzzies" using a star atlas and then "star hopping". Since the modern PC and laptop has become a normal inclusion in nearly every home, it has become mainstream to adopt computerisation into other areas of life, and the majority of the younger population in many countries around the world, now feel lost without being in constant touch with their multi-media mobile phones or laptops. Whatever it is, if its computerised, it takes on a certain desirability for a sizable portion of the population.
The computerisation of telescopes for amateur astronomy, so-called GOTO telescopes and GOTO mounts have appealed to a new generation of amateurs, that consider instruments that respond to commands and that move rapidly from one object to another at the touch of a button, as a pretty cool thing to own. Where previously, professional and academic observatories were the only places where computer controlled telescopes could be found, now we can all have one. Not only that, but now we can control them from inside the house, watch the moon and planets live and in real time on a laptop monitor, imaged by a telescope outside in the back garden, and even see faint objects live on a monitor with the aid of an extremely light-sensitive CCD camera attached to the telescope. The revolution of the personal computer and CCD camera has turned backyard astronomers into professional standard imagers, and the hobby generally into a "gather round" family and neighbour activity.
Before we look at how a GOTO helps astronomers, and note the advantages and any disadvantages, we need to know how a GOTO system works. As a GOTO system is associated with mounts and not telescope tube assemblies, we can accept that the following is good for complete GOTO telescopes as well as GOTO mounts on their own.
GOTO mounts are manufactured in both alt-azimuth and German equatorial designs. Both are fundamentally the same in that they include a handset or hand-pad that contains a database of stars, deep-sky objects (DSO), planets, the Sun and moon, plus a few other objects of some interest. The database includes the position in RA and Dec. or altitude and azimuth for all these objects, and some GOTO systems include other interesting data about each object, as a form of education or just casual information. GOTO mounts have a motor on both axis, and a motor control circuit board that receives commands from the handset, and signals the motors to move the mount by a given amount so that the telescope is pointing at the desired object. Before it can do that it requires certain information by the user. In order for the telescope to "go to" an object by pointing the mount, the user needs to input into the handset, the current date, time, location on Earth (either latitude and longitude, or failing that, the nearest city in the database scroll list), the time zone (GMT, California, Germany, Australia etc.), and whether Daylight Savings or Standard Time. Some larger GOTO telescopes include a GPS unit that automatically downloads the date, time and location data from a satellite. For those that don't, it needs to be inputted by the user. Once the computer in the handset knows when and where on Earth it is, the next stage is to commence an alignment process. There is usually a choice of alignment options in the alignment menu such as Single star, Two star, Auto two star, Solar system align and even alignment that does not require knowledge of the names of any stars. Lets choose Auto two star. The user presses the altitude and azimuth slew buttons on the handset in order to move the telescope quickly to point at a given star, let's say Vega. When Vega is in the centre of the eyepiece, the user presses Enter or OK. A scroll list appears giving a choice of second alignment stars. Let's say we choose Capella. We press Enter or OK again and this time the mount moves automatically and points the telescope at where it thinks Capella should be. If the star is somewhere in the field of the eyepiece, or even outside, we slowly slew the star into the centre of the field and press Enter or OK again. Align success! The computer now knows where everything in the sky is and can point the telescope to any object or co-ordinate it is commanded to. The mount slews quickly to a close proximity of the object, slows the slew rate (ramps down), and finally drift-slews the star into the field of the eyepiece and then stops. From that point the motors begin at tracking rate to track the object so that it remains in the eyepiece field. For the rest of the night or until the mount is switched off, no more user input is required. There are usually three tracking rates to choose from - Sidereal (for the stars, planets and DSOs), Solar, and Lunar.
The pointing accuracy of GOTO mounts depends heavily on input. That is to say the more information the handset has, the more accurately it can point at an object. Many astronomers will, during the course of an observing session, confirm or tighten the alignment accuracy by choosing another and then another star at interval to align on, in different regions of the sky. This helps to "nudge" the position of the sky map onboard the handset a little, so that its positional sense slowly becomes more perfect. GOTOs often have a Sync function, which is a way of concentrating pointing accuracy at one star and its surroundings. This is useful for deep-sky observing in one area of the sky, at the expense of pointing accuracy in all other areas of the sky.
Many GOTO systems can interact with astronomical information websites for downloading positional data of comets and asteroids, and manufacturers include on their websites, the facility for downloading improved firmware for their handsets and motor circuit boards, as a periodic upgrade. Most GOTO systems also interact with planetarium software programs, with the facility to control the mount from within the program.
GOTO mounts require DC power in order to operate. Usually this is 12v DC. Some smaller GOTO telescopes and mounts have the facility to use AA alkaline batteries although the reliability of small 1.5v batteries in cold temperatures may be limited. Many mounts can be powered from a 230v AC to 12v DC adapters. For the reason of constantly smooth power delivery, a 12v DC lead acid battery such as that used in portable Powerpacks and Powertanks are the best choice. A 12v car battery is ideal although the cable connection between these batteries and the telescope may be a little inconvenient.
The difference between alt-azimuth GOTOs and equatorial GOTOs is that for an equatorial, tracking is in RA only. For an alt-azimuth tracking an object requires both motors to run at the same time. Because the mount is not polar aligned, the star will drift in declination. The computer prompts the motor-board to control the motors so that each motor is running at the correct speed to keep the star within the field of the eyepiece. Long exposure astrophotography is not possible with an alt-azimuth GOTO telescope, unless the telescope can be placed onto an equatorial wedge and polar aligned, in which case it becomes an equatorial telescope.
Each manufacturer boasts small advantages in their GOTO over a rivals system, and although some are easier and a little more intuitive to use than others, they operate in a similar way. The latest type of GOTO telescope for those new to astronomy that dislike electro technology generally, is one that has an onboard camera. When switched on it takes images of a small area the sky and matches them to its onboard database. After three matches are found the mount is aligned ready for use. It requires no input at all from the user apart from simply switching it on.
Advantages of a GOTO mount.
a.) Enables a beginner to feel a sense of inclusion in the hobby alongside his/her more experienced peers.
b.) Imaging as an aspect of the hobby can be taken up earlier than with a non-GOTO mount.
c.) A greater number of deep-sky objects and even the fainter planets can be viewed, where they may have been ignored as too time consuming to find without the GOTO.
d.) Enables a much greater number of objects to be viewed in one observing session. Modern life is somewhat rushed, a GOTO mount helps with the inclusion of observing or imaging sessions into a schedule.
Disadvantages of a GOTO mount.
a.) Usually much more expensive than the same mount without a GOTO.
b.) Removes the education aspect from learning the night sky. Those brought up on non-GOTO telescopes such as experienced Dobsonian users, can often find an object quicker than a GOTO can slew to it. Not relying on a GOTO improves astronomical positioning knowledge. The observer contains the database rather than a handset.