Accurate polar alignment of a German equatorial mount is essential in order to undertake long-exposure astroimaging, otherwise your final resulting images will show trailed stars or field rotation. Furthermore, precise tracking of celestial objects also depends on an accurate polar alignment. For Northern-hemisphere astronomers, Polaris is very near the North Celestial Pole (NCP), but the true celestial pole’s location can still be difficult to find without some assistance.
Celestron’s All-Star™ Polar Alignment feature can help with this.
All-Star is an innovative polar alignment procedure—available on selected Celestron computerised telescopes—that allows any bright star (not just a one near the NCP) to be chosen while the software calculates and assists with the mount’s polar alignment.
So how does it work? Once the telescope is aligned with two or more bright stars, All-Star allows you to choose any bright star listed in the NexStar hand control. This star will assist the software in correctly aligning your telescope’s mount with the North Celestial Pole.
Using the telescope’s Sync function, the mount will point to, and centre, a bright star with a high degree of accuracy. Once centred, the mount will point the telescope to the exact position that the star should be if the mount was precisely polar-aligned. When you adjust the mount’s altitude and azimuth adjustment controls to re-centre the star in the eyepiece (NOT using the hand controller to move the mount!), you are actually moving the mount’s polar axis to the exact position of the North Celestial Pole.
For best results, Celestron suggest that a bright alignment star that is near the Meridian, preferably close to the celestial equator is chosen. Furthermore, it is recommended to avoid stars that are close to the west/east horizon or directly overhead. These stars can be more difficult to centre using the mount’s altitude and azimuth controls. Also, stars too near the celestial pole are less accurate than those further away.
The mount will retain its alignment after the All-Star Polar Alignment routine is complete, but some amount of accuracy may be compromised depending on how much the mount was moved during polar alignment. Although the telescope’s tracking may be very good, pointing accuracy may need to be improved, especially if you are trying to locate small objects on a CCD chip.
To help you polar align your mount using All-Star Polar Alignment here is an outline procedure:
- Align the telescope with the sky using the Two-Star Alignment method.
- Align to at least one calibration star on the opposite side of the meridian.
- Select a suitable bright star from the NexStar hand control’s database. Slew the telescope to the star.
- Press the Align button. Select “Polar Align” then “Align Mount” from the list.
- The telescope will then re-slew to the alignment star and ask you to center it in the eyepiece in order to “sync” on the star.
- The telescope will slew to the position that the star should be if it were accurately polar-aligned.
- Use the mount’s altitude and azimuth adjustments to center the star in the eyepiece.
- Press the Align button.
- If necessary, update the telescope’s star alignment.