Polar Aligning an Equatorial Mount for Use of Manual Setting Circles

1. Polar Aligning an Equatorial Mount for Use of Manual Setting Circles Chris Waskey www.geocities.com/waskeyc waskeyc@yahoo.com

2. German Equatorial Mount

3. Useful Links • Tons of great information • www.cloudynights.com • Free Star Charts to Mag. 7 • http://www.cloudynights.com/item.php?item_id=1052 • Daily celestial events, updated weekly • http://www.skyandtelescope.com/observing/ataglance?1=1 • Source for most of this presentation • http://www.skyandtelescope.com/howto/visualobserving/3304206.html?page=1&c=y • Free TriAtlas for download and print, virtually all known DSOs • http://www.uv.es/jrtorres/index.html

4. Outline • Background/Purpose • Setting Up Initially • Checking and adjusting the mount in daylight • Setting Up and Observing • Polar Alignment • Navigating • Troubleshooting • Conclusions

5. Background • Celestial Coordinates • Declination is measured from the celestial equator • Degrees north or south • True at all times • Right ascension (R.A.) is measured from the location of the sun at the Vernal Equinox • Hours and minutes, increasing to the East • Local meridian R.A. changes as the earth rotates

6. Background: Celestial Coordinates

7. Background: Mount Axes • Polar Axis / Right Ascension Axis – points to the celestial poles. When the telescope is rotated about this axis, the R.A. value changes. • Declination Axis / Counterweight Axis – perpendicular to the polar axis, the axis that the counterweight bar screws into. When the telescope is moved about this axis, the Declination changes

8. Purpose • Accurate polar alignment helps with: • Tracking objects at high magnification • Long-Exposure Astrophotography • Use of manual setting circles

9. Purpose: the Goal

10. Setting Up the Telescope • Do once and forget • Goal is to identify polar axis of mount, then adjust Declination axis to be perpendicular to it

11. Setup: Finding Polar Axis • Setup Mount Polar Axis facing a horizontal line • May be horizon or horizontal roofline, etc • Turn scope to 90o Declination and rotate in R.A. so counterweight bar is horizontal • Adjust mount elevation so horizon is centered in the finder scope • Rotate scope 180o in R.A. and determine whether scope is pointing high or low • Adjust the Dec. to split the difference, then adjust the mount in elevation until the horizon is centered • Verify setting, permanently move the Dec. setting circle to indicate the new 90o

12. Setup: Adjust R.A. Axis to be Perpendicular to Polar Axis • After identifying 90o Declination, point the Polar Axis of the mount to a distant, identifiable object • Rotate the scope in R.A. 180o about the distant object • If it stays centered, you’re done • If not, you may need a spacer between one tube ring and the mounting bar

13. Observing • After preparing the telescope, it’s ready to setup and use • First accurately position the scope to 90o Declination and adjust the mount to align the Polar Axis with the North Celestial Pole (NCP) • Second, point the telescope to a known celestial object and set the R.A. dial • Third, move R.A. to coordinates of desired object, followed by Dec. to coordinates of object

14. Observing: Polar Alignment • Set up tripod roughly facing True North • Adjust Latitude to roughly local latitude (~37o N for Virginia) • Turn scope to roughly 90o Declination • Rotate scope in R.A. and alternately adjust Dec. and mount until center of rotation is on Polaris • Use mount adjustment screws to move center of rotation to NCP

15. Observing: Polar AlignmentNorth Celestial Pole

16. Observing: Polar AlignmentFinder View Orientation

17. Observing: Polar Alignment • To find the North Celestial Pole, look for the 6th magnitude star near Polaris • In a straight through OR correct image finder, go from the 6th magnitude star to Polaris, then turn RIGHT (otherwise turn left) • Move from Polaris almost halfway toward the first 6th magnitude star (λ) in the handle of the Little Dipper

18. Observing: Polar Alignment X

19. Observing: NavigatingVernier Scale • For approximate R.A., read the value on the dial closest to the zero on the vernier • For exact value, find the closest match on the vernier to a line on the R.A. scale (doesn’t matter which R.A. line that happens to be) • R.A. is # on vernier plus closest R.A. value below the zero • See example

20. Observing: NavigatingVernier Scale

21. Observing: Navigating • First, point the telescope to a celestial object with a known R.A. • Adjust the R.A. dial on the mount to the R.A. of the object • Move the scope to the R.A. of the desired object and lock the R.A. axis (if equipped, turn on drive motor) • Move the scope in Declination to the Dec. of the desired object

22. Observing: Troubleshooting • If all of the steps above were followed carefully and a reasonable magnification is used, the object should be in view • If it’s not in view, check these things: • Is the object in the finder scope view? • Is the object visible in your size telescope and current conditions? • Did too much time go by between setting R.A. dial and moving to the object’s R.A.? • If you still can’t find it, but should be able to see it, then try star hopping from a nearby known object

23. Conclusions • After adjusting the mount to set accurate Declination and to make the axes perpendicular, polar alignment should only take a few minutes • An accurate polar alignment can be used to find objects with manual setting circles, and can improve the accuracy of GOTO scopes

24. Questions?