Celestron 4 - page 27

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Eventhough 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 forkarm) 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 telescopeand a tripod. Celestron also offers a steel tripod with an attached wedge tilt plate (#93497). Thisallows

thetelescope's tracking motors to rotate the telescope around the celestial pole, the same way as the stars. Without the

equatorialwedge, you would notice the stars in the eyepiecewould slowly rotate around the center of the field ofview.

Although this gradualrotation would go unnoticed when viewing withan eyepiece, it would be very noticeable on

film.

Polaralignment is the process by which the telescope's axis of rotation (called the polar axis) is aligned (made parallel)

with the Earth'saxis of rotation. Oncealigned, a telescope with a clock drive will track the stars as they move across

the sky. The resultis that objects observed through the telescope appear stationary (i.e., they willnot drift out of the

fieldof view). If not using the clock drive, all objects in the sky (day or night) willslowly drift out of the field. This

motionis 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. Neveruse 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

northi s and more specifically where the North Star is.

The polaraxis is the axis around which the telescope rotates when moved in right ascension. This axis points

thesam ed irection even when the telescope moves in right ascension and declination.

In orderto do a star alignment while using the NexStar on an

equatorial wedge it will be necessary to use the Two-Star

alignmentmethod rather than the AutoAlign method. Before

the NexStar is attached to the wedge, slew the telescope so

thatthe tube is pointed straight up overhead (the tube should

beparallel to the fork arm). Attach the telescope to the wedge

and angle the wedge so that the NexStar's fork arm is

pointingtowards 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 th e

power on the NexStar and begin the Two-Star alignment

procedure as described in the Hand Control section of the

manual. When doing a Two-Star alignment while using an

equatorialwedge, remember the following:

When the hand control instructsyou to point the telescope

tube north and level, make sure that the tube is positioned

perpendicular (at a 90º angle) to the forkarm with the tube

facing down. This is the same position that you would have

thetube if you were aligning the telescope in Altazimuth.

Afterthe align ment is complete, remember that your slew and

filter limits are defined relative to the base of the telescope.

This means that an altitude slew limit of 80º instructs the

NexStarto avoid slewing to any objects that is closer than 10º

frombeing parallel with the fork arm.

Filter limitsshould be set so that the entire database will be displayed. Set the maximum altitude limit to read 90º and

theminimum altitude limit to –90º. Thiswill allow you to view and choose any object in thedatabase.

Definition

Figure6-3

Thisis 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.

Warning!