Celestron 93507 manual Few Words on GPS, GPS Alignment

GPS Alignment

GPS Align must be used with the telescope mounted in altazimuth. With GPS Align mode, the NexStar automatically levels the optical tube, its built-in electronic compass points the telescope in the direction of the northern horizon, while the GPS receiver links with and acquires information from 3 of the orbiting GPS satellites. With this information, the built-in GPS system calculates the scope’s location on Earth with an accuracy of a few meters and calculates universal time down to the second. After quickly making all these calculations and automatically entering the information for you, the NexStar GPS orients itself with the sky, slews to an alignment star and asks you to position the star in the center of the eyepiece. The NexStar is then ready to start finding and tracking any of the objects in its 40,000+ object database. Before the telescope is ready to be aligned, it should be set up in an outside location with all accessories (eyepiece, diagonal and finderscope) attached and lens cover removed as described in the Assembly section of the manual. Before turning on the NexStar, make sure that the tube is pointed downward and both the altitude and azimuth clutches are locked down. To begin the GPS alignment:

1.Power on the NexStar by flipping the switch located on the bottom portion of the drive base, to the "on" position. Once turned on the hand control display will say NexStar GPS. Press ENTER to choose GPS Align or use the UP/Down scroll keys (10) to select a different mode of alignment. Pressing the ALIGN key will bypass the other alignment options and the scrolling text and automatically begins GPS Align.

2.Once GPS Align has been selected, the telescope will begin to move to its north and level position. While the NexStar is positioning itself, the GPS receiver automatically begins to establish a link with the GPS satellites orbiting the Earth. The hand control screen will display the message GPS Linking to let you know that it is linking with the satellites.

3.Once the NexStar has established a link with the required

satellites,	the hand	control display will read GPS
Linked.	The	GPS satellites will then report the

current time and position directly to your NexStar. The NexStar now has all the necessary data to make a virtual model of the sky, select two bright stars for alignment and begin slewing to the first star.

4.When the NexStar has finished slewing to its first alignment star, the hand control display will ask you to use the arrow buttons to center the alignment star in the cross hairs of the finderscope. At this point the telescope is only roughly aligned, so the alignment star should only be close to the field of view of the finderscope. Once centered in the finderscope, press ENTER. If for some reason the chosen star is not visible (perhaps behind a tree or building) you can press the UNDO button to have the NexStar select and slew to a different star.

5.If the finderscope has been properly aligned with the telescope tube, the alignment star should now be visible inside the field of view of the eyepiece. The NexStar will ask that you center the bright alignment star in the center of the eyepiece and press the ALIGN button. This will accept the star as the first alignment position. (There is no need to adjust the slewing rate of the motors after each alignment step. The NexStar automatically selects the best slewing rate for aligning objects in both the finderscope and the eyepiece).

A Few Words on GPS:

The NexStar GPS uses an on-board GPS to take the guesswork out of aligning your telescope with the sky. Once GPS Align is selected, the NexStar automatically initiates the internal GPS module. However, there are a few things you should be aware of in order to get the full use of its many capabilities:

GPS alignment will only work when the telescope is set-up outdoors with an unobstructed view of the sky. If the NexStar is set-up in a location that has a limited horizon in any direction, the GPS alignment may still work, however it will take much longer for the telescope to find and link with the needed satellites.

When using GPS alignment for the first time, it may take 3-5 minutes for the NexStar to link-up with its satellites. Once the telescope is successfully linked, leave the telescope powered on for at least 20 minutes. During this time the NexStar will download the complete almanac of orbital elements (called the ephemeris) for the orbiting GPS satellites. Once this information is received it will be stored for future alignments.

If your NexStar is transported over a long distance (say from the northern to the southern hemisphere) it may take as long as one hour to establish a satellite link from its new location. Observers wishing to travel long distances with their telescope are advised to begin the GPS alignment in advance to allow the unit to acquire the necessary data.

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