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Generally a telescope can memorize how to point to a target with a particular RA&Dec. There is no need to calibrate every day.
How can it happen?
How to let the telescope(non-amateur) know the position of a star after it was built? For an amateur telescope, how to realize it? There should be a zero point?

How often should the calibration be?

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3 Answers 3

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First you have enter your coordinates into the mount's software and then align it(e.g. 3 star alignment).After having done that, when you finish the observation you have to park the telescope.

Actually Colin's answer is really helpful.They keyphrase is "After installation set up". The whole procedure should be explained in your telescope's manual. If you tell us which model you have we might be able to help more.

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  • $\begingroup$ So the telescope should observe some real targets to calibrate, right? Then the reference can be built. $\endgroup$
    – questionhang
    Jan 19, 2015 at 5:33
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    $\begingroup$ Yes that's the idea! After this is done there will be some error(hopefully small).So before you slew to a target you will slew to a bight star close to it.The telescope will be a bit off.Use the arrow keys on the handset to center the star on your field of view and press "enter".The telescope will correct its offset and then it will find your target with more accuracy. $\endgroup$
    – astromath
    Jan 19, 2015 at 7:42
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Telescopes will generally come with a library of objects, which includes information on where they are located on the celestial sphere.

There are two important pieces of information needed for the telescope to be able to locate objects from your Earthly location - Your position so that it knows its orientation relative to the celestial sphere, and the time so it can predict how that orientation will change.

When you initially set up your telescope, it will likely ask you first for the time, and then you will locate some easy to find objects. By finding three objects, the telescope will generally be able to understand its orientation relative to the celestial sphere.

At this point, it becomes trivial to find any object in its library, because it knows where the object is located, it now knows where it is, and it knows the time to adjust to changing in the Earth's orientation.

Even if power down your telescope, it takes very relatively little energy to track time and saving your location information is quite cheap. If the telescope can assume you're viewing from a relatively similar location, and it has kept track of the time, it has all the information it will need to find objects as soon as it starts up. As Colin said, if you change locations, you would then need to recalibrate as one of the key pieces of information the telescope is using would have changed.

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  • $\begingroup$ how about larger non-amateur telescopes? They should be the same? $\endgroup$
    – questionhang
    Jan 20, 2015 at 5:33
  • $\begingroup$ Some telescopes have built in GPS which do all the calibration for you. It depends more upon the electronic system than the actual telescope. $\endgroup$
    – Mitch Goshorn
    Jan 20, 2015 at 11:55
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After installation set up,the coordinates Ra and Dec are locked in to the ra of GMT(0 astronomically) and installation latitude.These are input requirements of installation. From that point,an onboard clock remembers all points from that reference. It is not a sat-nav base unit and installation would have to be repeated if repositioned in another location.

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  • $\begingroup$ Thank you. BUT it seems you answered nothing. How to REALIZE that? The telescope itself knows that? $\endgroup$
    – questionhang
    Jan 18, 2015 at 2:57

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