Celestron NexStar HC manual Polar Alignment with optional Wedge, Definition

Figure 7-3

This is how the telescope is to be set up for polar alignment. The tube should be parallel to the fork arm which should be pointed to Polaris.

Polar Alignment (with optional Wedge)

Warning!

Definition

Even though the NexStar can precisely track a celestial object while in the Alt-Az position, it is still necessary to align the polar axis of the telescope (the fork arm) to the Earth's axis on rotation in order to attempt long exposure astro photography. To do an accurate polar alignment, the NexStar requires an optional equatorial wedge (#93658) between the telescope and a tripod. Celestron also offers a steel tripod with an attached wedge tilt plate (#93497). This allows the telescope's tracking motors to rotate the telescope around the celestial pole, the same way as the stars. Without the equatorial wedge, you would notice the stars in the eyepiece would slowly rotate around the center of the field of view. Although this gradual rotation would go unnoticed when viewing with an eyepiece, it would be very noticeable on film.

Polar alignment is the process by which the telescope's axis of rotation (called the polar axis) is aligned (made parallel) with the Earth's axis of rotation. Once aligned, a telescope with a clock drive will track the stars as they move across the sky. The result is that objects observed through the telescope appear stationary (i.e., they will not drift out of the field of view). If not using the clock drive, all objects in the sky (day or night) will slowly drift out of the field. This motion is caused by the Earth's rotation.

Remember, whenever attaching the NexStar to the NexStar tripod or wedge, always use the bolts that come with the accessory. Never use bolts that thread more than 3/8" into the bottom of the NexStar base. Threading bolts more than 3/8" into the base will damage the internal gears.

Whether you are using your NexStar in the Alt-Az configuration or polar aligned, it will be necessary to locate where north is and more specifically where the North Star is.

The polar axis is the axis around which the telescope rotates when moved in right ascension. This axis points the same direction even when the telescope moves in right ascension and declination.

Aligning the NexStar 4 on a Wedge

In order to do a star alignment while using the NexStar on an equatorial wedge it will be necessary to alter some of the alignment procedures when doing the AutoAlign. Before the NexStar is attached to the wedge, slew the telescope so that the tube is pointed straight up overhead (the tube should be parallel to the fork arm). Attach the telescope to the wedge and angle the wedge so that the NexStar's fork arm is pointing towards Polaris. Move the tripod side to side and tilt the wedge up and down until Polaris is aligned in the StarPointer and visible in the eyepiece. Now recycle the power on the NexStar and begin the AutoAlign procedure as follows:

1.When the hand control asks you to point the tube north and level, use the arrow keys to rotate the telescope tube downward until the tube is perpendicular (at 90º) with the fork arm.

2.Continue to enter the date and time as requested. When asked to "choose location", you must scroll

down to the Enter Long / Lat option. Since the telescope's fork arm is pointed at the celestial pole

(Polaris), you will need to enter location information as if you were doing an Alt-Az alignment from the North Pole. To accomplish this, when asked for your locations latitude, input the number +89º (-89º for observing in the southern

hemisphere). When asked for longitude, input the longitude for your current location. A list of longitudes and latitudes can be obtained in most Atlases or on the Celestron web site. You will probably want to save this location in the database if you will be observing often from an equatorial wedge.

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