latest alignment object.  Because there are several parameters in the model, it won' t 

converge on nominal values until you have performed at least 4 or 5 alignments on one 

side of the meridian.  As mentioned earlier, you will get the best results if you pick 

alignment objects with substantially different hour angles.   An additional source of 

inaccuracy   gear play   is calculated with the first alignment on the opposite side of the 

meridian. 

3.5.2  System Startup Modes 

Because Gemini stores the modeling parameters in non volatile memory, it may be 

powered off at any time without losing its pointing model. In fact, the model can continue 

to be refined from observing session to observing session by adding more alignment 

points.  However, the modeling parameters are only valid if the telescope and mount have 

not been moved between observing sessions.  Whenever you turn the Gemini unit on, you 

need to tell it whether anything has been moved since it was turned off.  This allows 

Gemini to decide how much of the model is still valid.  There are 3 startup modes that tell 

Gemini what has been moved: 

Cold Start

Warm Start

Warm Restart

When the Gemini is powered up for the first time or after a CMOS reset, "Cold Start" is 

the only menu choice since there was no valid model in memory.  Once a model has been 

established, subsequent power ups will add "Warm Start" and "Warm Restart" to the 

startup menu. 

"Cold Start" is the "start from scratch" startup choice because it deletes all previously 

established model parameters derived from previous alignments.  It is the startup mode 

that must be used anytime the mount has been moved from its previous polar aligned 

position. 

Upon selecting "Cold Start,   Gemini allows you to change the UTC Date/Time, 

Longitude, and Latitude (level 3 version 1.01 and higher).  You should enter these 

parameters at this point unless they are still valid from a previous observation, or were 

provided by a GPS receiver that was connected to the Gemini when it was powered on.  

For Gemini version previous to level 3 version 1.01, you should use the   Setup   menu to 

change these parameters if necessary. 

Assuming Gemini was powered on with the telescope in Startup Position, the user can 

easily find a first alignment star by navigating to the "Databases" menu, selecting a star 

from the Bright Star Catalog, performing a GoTo operation, centering the star in the 

telescope 

s field of view, and then selecting "Synchronize."  This constitutes the initial 

star alignment in the process of building a pointing model.  Subsequent star alignments 

can then be performed one at a time by slewing (via GoTo) to other Bright Stars, 

centering, and executing "Additional Align." 

Gemini Users Manual 

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