determined.  You can read more about the various modeling parameters that Gemini uses 

in chapter 3. 

As mentioned earlier, there are several modes in which Gemini can start up.   For the 

purposes of this section, we will assume that the mount was   Cold Started.    Subsequent 

sections of the manual will explain the modeling and alignment process in greater detail 

for each of the 3 startup modes. 

2.4.3.1  Choosing Alignment Stars 

Unless you are perfectly polar aligned and have no mechanical play or misalignment in 

your mount and your telescope, you will need at least 3 star alignments in order to build 

an accurate model.  These must all be on the same side of the meridian   either east or 

west.  The first 3 alignment stars should be selected from Gemini 

s "Bright Stars" catalog 

(database) and must differ in hour angle (distance in RA from the meridian) by at least 

one or two hours.  This means you either need to choose stars that differ in RA by at least 

a couple hours, or wait a couple hours between alignments so that your next alignment 

star will differ in hour angle from where your first alignment star was.  For example, 

doing an alignment on Capella and then on Rigel or Bellatrix is not a good idea; the same 

is true for alignments on Procyon, followed by Castor or Pollux   there are only tiny 

differences in RA between them. 

Make sure that you are certain of the identification of all stars that you use for alignment.  

If you misidentify a star that is far from the correct star, Gemini will reject the 

  Additional Alignment.    However, if you align on the wrong star that is close to the 

correct star, Gemini will accept the erroneous   Additional Alignment,   and errors will be 

introduced into the pointing model causing inaccurate GoTo operation. 

2.4.3.2  Slewing to and Aligning on your First Star 

After you have pre selected 3 alignment stars, you are ready to start the alignment 

process.  When you cold started, Gemini assumed that the mount was perfectly polar 

aligned, level, in the counterweight down position, and that the telescope was pointing 

north (or south in the southern hemisphere).  It then built an initial model based on these 

assumptions. 

 Having selected your 3 bright alignment stars, you now need to select and GoTo the first 

one.  The easiest way to do this is to select the   Align Telescope

GoTo Bright Star   

from the menu.  You can then use the DEC buttons to scroll through the list of Bright 

Stars that are currently above the horizon.  When you see the name of the star you want 

to use, press the RA+ button, and Gemini will slew close to that star.  Depending on how 

well you polar aligned your mount and assuming that your location, date, and time are all 

accurate, the target star may even be in the field of view of a low power eyepiece.  The 

Hand Controller will now be in Telescope Control Mode, and you should use its buttons 

(with the aid of a finder scope if necessary) to locate and center the star in your eyepiece.  

Once the star is centered, press the   Menu   button to enter Menu Mode, and select  

  Align Telescope

Synchronize.    It will confirm the object you are pointing to.  Finally, 

press RA+ to complete the first step of alignment. 

Gemini Users Manual 

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