Uncle Rod's Astro Blog: The Polar Alignment Party. This Sunday. morning, muchachos, you Dob and alt- azimuth mount users can sit back, have a. Joe, and be glad you don’t have to join our little party.
If you are an. equatorial mount user, though, especially a new. First things. first, I reckon. If you read my epistle on German equatorial mounts not too long back, you know an equatorial mount is. Oh, you can use gadgets like. That means most of us doing imaging. For an EQ mount to be able to track satisfactorily, it must be set.
It must have its right ascension (east- west) axis aimed at the. The whosits. of the whatsits?” If you are a novice, or are just new to the world of.
The stars move across the sky. To counter that rotation, an equatorial mount.
Where. the heck is that? As I tell my freshmen astronomy students, the easiest way to. Suspension of Disbelief. For a. minute, let’s consider that old Ptolemy and his bubbas were right: the sky is a. Earth. The lines on. Earth are all repeated on this sky globe.
If you extend the. Earth onto the sky globe it becomes the celestial equator. Lines. of latitude become lines of declination. Lines of longitude become lines of. AND…if you extend the axis of the earth into the sky globe, it. Celestial Pole, "hitting" the sky globe at a spot near.
Polaris (North Celestial Pole) or Sigma Octanis (South Celestial Pole). While it’s. the Earth that is rotating, from our perspective it appears the sky globe is. Celestial Poles. That being.
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Celestial. Pole’s axis, and drove it at a speed matching the sky globe’s rotation speed. Part of the. equation for good tracking is the motors, gears, and computers, that drive the. Earth’s rotation axis by. R. A. axis at the North Celestial Pole is just as important or moreso. If you are “off,” the scope will not track precisely, no matter how good the.
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OK, so how do you do this. Glad you. asked. No matter. You can do that one of two ways.
If you are antsy. Begin with the mount/scope plunked down roughly. Southern Hemisphere boys and girls) and the tube.
If you’re using a fork mount scope, the. If you’ve got a GEM, the tube. R. A. housing. Now it’s. If you have a wedge- mounted SCT, you either loosen a.
Meade). or the bolts that hold wedge on tripod (Celestron). Get the compass out and.
Stand back from the scope far enough so the. R. A. housing’s position with regard to north/south.
Need to go a little left? Move. it left a little in azimuth.
A little right? Do that. Most GEMs. have a pair of bolts that push against a post on the tripod.
Screw in the bolt. A wedge is either just manhandled left or right (sometimes, like the old. Celestron Celestar, by nudging the tripod) or with an azimuth adjuster that. After that? That's. Rough polar alignment is done. How rough is it? You might get lucky and be.
What you will usually get is “good enough for visual.”. You will have to mash a north or south button or turn a slow motion control. If it is too bad, you can wait for dark and do. A better. rough alignment requires one thing: that you be able to see the pole star. In. the north, that’s easy unless there are obstructions.
Polaris is magnitude 2. In the. south, the pole star, Sigma Octanis (or “Octantis” if you prefer), is not as.
It is at magnitude 5. Not. sure which star is Sigma? It forms a little parallelogram with Tau, Upsilon. Chi Octanis. Wait for sufficient. Cartes du Ciel or. What do you. do with the pole star? You center it in the telescope’s finder (or in the polar.
GEM). If your GEM does not have a polar scope in its. RA housing, just center Polaris in the hollow bore. Unless your eyes and skies are pretty dern good, you will have to use the scope’s main finder for Sigma.
What does this. better rough- in get you? Tracking most assuredly good enough for most visual. It will not be perfect, since Polaris is about ¾- degree from the true North Celestial Pole, and Sigma, which occasionally goes by the name.
Polaris Australis,” is about 1- degree from the South Pole. While the. two rough methods are good enough for many purposes, if you are imaging or. Where does. that better start? If you have a GEM, it starts with a GEM mount’s polar. More Better Gooder. A GEM’s polar. finder is a simple device; it is a little refractor inserted through the hollow.
R. A. axis of the mount. It will have a special reticle that may have pictures. Polaris goes. Most polar scopes have reticles that also accommodate. Southern Hemisphere observers. Rough- in the. telescope as above, and remove the fore and aft lens- caps from the mount’s R.
A. housing. You will have to turn the telescope (or just the mount’s saddle if the. R. A. axis of the mount. How do you. do the actual alignment?
There are several possibilities. You can use the. etched constellation figures, if any. Undo the R. A. lock and rotate the mount. Note that the constellation etchings (usually Ursa. Major and Cassiopeia in the Northern Hemisphere) will not be able to be overlaid. Just eyeball. the real things in the sky and match their rotational orientation as well as. When done, lock the R.
A. axis, and use the mount’s altitude and. Be sure to tighten down the mount’s altitude and azimuth so. The “match. the constellations” method is better than just centering Polaris, but it’s not overly. You can get that by using. The manual that came with the GEM. Stuff that. is confusing for beginners and everybody else.
Luckily, there is a simpler way. The simpler way. Polaris’ (or Sigma’s) “Local Hour Angle.”. Hour Angle is a sort of time that indicates the position of the pole star with. To use the LHA method, rotate the mount in R. A. until. the circle (or other marker) on the polar scope reticle where Polaris goes is on the bottom. If the. reticle has a crosshair above the circle, you can get it exact by centering the. When the marker for the.
R. A. and set the R. A. setting circle to “0” hours. Now, find. the current hour angle of Polaris. How do you do that? If you are using a Synta. Syn. Scan mount (like the Orion Atlas EQ- 6), its hand controller will display LHA. If you are not? Some planetarium programs.
Cartes du. Ciel, show LHA (click on Polaris and bring up the information window for. So do Polar Alignment helper programs (more on them in a minute). There. are even i. Phone programs that display Hour Angle. When you. have Local Hour Angle, undo the R. A. lock and rotate the R.
A. axis of the mount. Northern Hemisphere) is the same as the current LHA. If LHA is. 1. 4: 3. R. A. under the pointer is 1.
Lock. the R. A. axis again and use the altitude and azimuth adjusters to move Polaris to. When done carefully, the LHA method will. Potential gotchas? Be sure the polar scope is correctly aligned with the mount (see the manual.
Newbies: some of y’all assume you turn the polar scope in its housing till the reticle is properly. Nope. Like I been saying, you. R. A. lock and rotating in right. I like the. LHA method of polar alignment a lot, but there is another way to use a polar. That is the “Kochab’s Clock” procedure of my.
Doc Clay Sherrod. If you have a GEM (and, natch, live in the Northern. Hemisphere), this is an easy way to get the Polaris marker in your polar scope. With the mount pointed north and ready to go, find the. Kochab, Beta Ursae Monoris. Undo the R. A. lock, and.
Lock R. A. Move the. Polaris is in the correct spot. For full. instructions, see this nice page.“All that’s.
GEMs, Unk, but I got me a Meade 2. SCT that ain’t got no polar. A few companies used to sell add- on polar scopes for forks, but all of. Jim’s Mobile. Quite a few SCTs from the 1. OK alignments. But if the. Doc Clay has a somewhat more complicated but very. Kochab’s Clock alignment for fork users that can be found here. It.
SCT. finder, even one without a polar reticle. While this take on the Kochab Clock. I would guess that today most fork users, those with computer. Hand Paddle Polar Alignment. Need to kick. it up at least part of a notch in accuracy and a big notch in “easy”?
Some. mount makers, most notably Synta/Celestron and Losmandy, have been incorporating. It works like. this: you do a go- to alignment after.
It has you select and go- to a star. The mount then points at where. All you’ve. got to do then is center up the star using the mount’s altitude and azimuth. The good? This. alignment method is quite accurate, at least as accurate as a polar scope. There’s no kneeling down on the cold hard.
And, to top it all off, go- to. GEM. The bad? While. Polaris or Sigma, which is a god- send. Celestron. suggests with the name for their polar alignment process, “All. Star,” use any star.
To begin with, they recommend. Polaris, and while you can use any other. Celestial Equator and the Local Meridian, it becomes a bear to center a. All in all, though, automated polar alignment. What if. you’ve got a go- to, but it ain’t a Celestron or a Losmandy and doesn’t have a. All is not lost. You can use another accurate computer.
This process, “Iterative” alignment, is not as quick as All. Star but is. at least as accurate. Its only potential drawback is that you must be able to. Polaris or Sigma. It seems a. little complicated the first time out, but once you’ve done "Iterative". To begin, rough in the polar alignment as always, go- to align the scope (some. The only criteria for star.
When you’ve. picked and done a go- to to the star, center it up with the hand control and. SYNC it. Then, go- to Polaris (or Sigma). Don’t. sync here; use the alt- az adjusters to move the star HALF the distance to the center of the eyepiece. Next, go- to the. HC buttons and sync, go back to the.
Keep going. back and forth till Polaris (Sigma) is dead center after a go- to. When it is, you. are done and have a very good alignment. You are one. of my brothers or sisters who take loooong exposures? You, like Rod, stack your. Unk’s 2 – 5- minute “subs,” yours are. If that is you, you need an exact polar alignment.
Yep, you gotta drift align, as in “use the declination. Some folks. including Unk, who don’t have observatories and must polar align every time. After. you’ve done it a couple of times, you can probably be up and aligned in.