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Celestron’s CN-16 GPS is used to give the telescope mount time-site information.

To determine exactly what the GPS unit will do with your scope, the different versions of both the GPS and NexStar-i series mounts need to be considered.

There have been two major versions of the CN-16. The older version incorporated a ball bearing switch, used to help the unit determine level and direction when attached to a telescope. The newer version doesn’t have the bearing switch and doesn’t provide this information. Gently shake the CN-16 to determine which one you have: the older version will rattle.

The NexStar i-series itself also has two major subdivisions: older models that use the north and level alignment method and newer models that don’t. Older NexStar-i series mounts with hand control versions 2.2 and 2.3 are north and level mounts. Newer mounts with higher-numbered hand control versions aren’t. They use the newer SkyAlign method.

An older CN-16 will go on top of an old i-series scope tube attached with a bracket that comes with the GPS. Plug it into the AUX port on the base and it will power on and the red LED light will glow. Enable the GPS by pressing MENU > UTILITIES > GPS ON/OFF, choose On and press ENTER. The GPS will link with the GPS satellite constellation, providing time-site information, while the mount moves, allowing the GPS to provide north-level information too.

An older CN-16 with a newer i-series scope can only give the mount what it will take, which is time-site information. It can be attached anywhere, since the north and level input is not used. Plug in and enable the GPS as before.

A newer CN-16 with an older i-series scope can’t be used with the scope’s GPS ALIGNMENT mode, since the GPS only supplies the time-site information and not any north-level information. Plug in and enable the GPS as before.

A newer CN-16 with a newer i-series scope provides the scope’s mount with time-site information after the GPS is plugged in and enabled.