Astronomical Society of Geelong 

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The NEW ASOG Website
This is our 'brand-new-squeaky-clean-with-bells-and-whistles-
attached' website!
We hope you find our website an informative one for you, and that you find all the information you need about our club and hopefully join it as well as what you need to know about the basics of Astronomy.

The science of Astronomy is a wonderful and rewarding thing and many members dedicate many hours, days, weeks even years into this branch of science.

Please feel free to wander around and ask any questions about the club, on the committee page and that will link you to their corresponding email. Hopefully your question will be answered very quickly. In the meantime enjoy your browsing the website and clear skies to you.

Different types of telescope mounts

To a large extent, a telescope is only as good as its tripod and mounting. A telescope is used to magnify the sky, but unfortunately it also magnifies vibrations.
A telescope mount has two primary functions:

  1. Support the telescope firmly so that objects can be viewed and photographed without vibrations

  2. Provide a system for smooth controlled movement to point and guide the instrument

There are two major types of mounts for astronomical telescopes: Altazimuth and Equatorial.

Altazimuth (sometimes called alt-az) is the simplest type of mount with two motions, altitude (vertical) and azimuth (horizontal): thus the name Altazimuth.
Good Altazimuth mounts have slow-motion knobs for making precise adjustments, aiding smooth tracking across the sky. These type mounts are generally good for terrestrial observing and for scanning the sky at lower power but not for deep sky photography. Some Altazimuth mounts are now computer driven and allow a telescope to track the sky more accurately. This is generally good for visual use but can lose tracking on longer exposure astrophotography.
In addition to a standard Altazimuth, mounted on the top of a tripod, there is also the Dobsonian Mount.

Dobsonian Mount
The Dobsonian mount is a newer, modified version of the Altazimuth mount. This mount was invented in the 1970's by John Dobsonian. Dobsonian mounts are mounted on the ground by a heavy platform, and designed to support massively sized Newtonian Reflectors, while keeping a steady image. It is common for Dobsonian telescopes to have very large apertures - anywhere between 6 and 20+ inches!

Equatorial mounts are superior to non-computerised Altazimuth mounts for astronomical observing over long periods of time and absolutely necessary for astrophotography. As the earth rotates around its axis, the stationary stars appear to move across the sky. If you are observing them using an Altazimuth mount, they will quickly float out of view in both axes. A telescope on a properly aligned equatorial mount can be aimed at a celestial object and easily guided either by either manual slow-motion controls or by an electric motor.

There are two relatively simple steps to aligning your equatorial mount:

  1. Position the tripod so that it points along a line with celestial south. The tripod can be placed pointing anywhere in a 360 degree circle, but you want the front of the mount aiming south. Do not confuse this with magnetic south, as they are not aligned! Some mounts are equipped with a device for rotating the telescope, which can be pointed south instead of aligning the tripod itself. 

  2. The first joint above the tripod allows adjusting the telescope to be tilted back. This needs to be tilted to the same number of degrees as the viewer's latitude. Once this is done, the telescope should be pointing at the celestial South Pole.

There are two basic types of equatorial mounts:
German Equatorial Mount
Both Newtonian Reflectors and Refractor telescopes normally use this type mount. The German Equatorial mount’s distinguishing feature is the large counterweight extending on the opposite side from the telescope. This counterweight is vital, as it provides balance to the telescope.

Fork Mount
Most Catadioptric and other shorter optical tubes use this style mount, which is generally more convenient to use than the German mount, especially for astrophotography. A computer controls the telescope using an internal, digital equatorial drive to calculate the Altazimuth setting for the mount. This is the style of mount most commonly used in modern research telescopes. This fully automatic operation can make observing extremely fun and easy, while saving the observer considerable time and effort in locating objects. With this type of mount, you will often only need to align the telescope to celestial south, and enter your latitude and longitude, and the computer will do the rest.

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