After spending a LOT of clear sky time trying to get the hang of drift aligning and also trying to figure out which way is which in the scope and finder, I thought I might have a go at actually targeting the South Celestial Pole (SCP) using my shiny new 11x70 Binoculars, figure out where it is, set the scope in the right direction and therefore eliminate the drift when using a motor drive on the RA axis. Something in my initial setup didn’t feel right and as a consequence I have come up with this star hopping method to help any newbies out there get their Equatorial mount set up quickly and (hopefully) accurately. Without knowing what you are actually LOOKING for, it becomes extremely frustrating to try and find this elusive beast. I have combined some sage advice from the experts on IIS and my own observations to come up with a solution.
Please note, these instructions assume the following:
1) You have either some binoculars or other magnifying device like a finderscope (5x30) or better, to zero in on the areas listed.
2) That you can actually SEE stars and constellations in the direction of the SCP, or most importantly Archenar, Crux and Alpha Centauri. ie no clouds and little light pollution.
3) You know how to adjust your Latitude (altitude) and Declination settings on your mount.
4) You are physically capable of moving your mount around.
5) You want to get polar aligned fast.
6) Your brain hurts trying to figure out drift aligning. (think standing in back yard with arms flapping around looking like a goose.)
7) You won’t hold me responsible if this doesn’t work for you.
OK, with reference to the attached diagrams, here we go.
1) Adjust (if possible) the tripod so that one of the tripod legs points roughly south (using a compass) and that the mount is lined up along this tripod leg. I normally set the south pointing leg to around 168˚ which is True South for Sydney. Make sure your tripod is roughly level.
2) Set your telescope mount to 90˚ Declination (this is the direction of the SCP) and your scope’s tube should be in line with the south pointing leg.
3) Find Archenar (labeled 1 in attachment 1) in the sky, this will be your starting point.
4) Look towards Crux and Alpha/Beta Centauri. Draw an imaginary line (YELLOW) in the sky between Alpha Centauri and Archenar, you will notice that this line passes close to a star in the constellation of Hydrus (Beta Hydrus – marked as 2) as well as the Small Magellanic Cloud (SMC – if visible). Alpha, Beta and Gamma in Hydrus form a triangle that is “almost” an equilateral (equal sided) one in the sky and Beta Hydrus has a small star off to one side which helps you know you are on the right one.
5) From Beta Hydrus (point 2) look toward the Southern Cross (Crux) and draw an imaginary line (GREEN) between Beta Hydrus and Acrux (the star on the bottom of the cross, furthest away from the others). This line passes very close to the SCP, but never fear, we will get there soon…
6) Using the imaginary green line and starting from Beta Hydrus, move slowly along this line using your finderscope or binoculars and you will quickly see a group of three stars arranged a little like the hands of a clock pointing to 5 minutes past 6. These are Gamma1, Gamma2 and Gamma3 of Octans constellation (attachment 2 & point 3). Keep a note of the distance between Beta Hydrus and these stars, you are now going to double this distance along this line to find Sigma Octanis and friends.
7) From Gamma1-3 Octanis, keep going along the green line towards Acrux the same distance and you should come across 3 brightish stars arranged in a triangle (point 4) these are Sigma Octanis on top, Chi and Tau Octanis. We are now VERY close to the SCP. Sigma Octanis has a small star off to one side nearby.
8) Create an imaginary equilateral triangle using Tau and Chi Octanis that encloses Sigma Octanis (attachment 3). The point of this new triangle is the SCP.
9) Adjust your scope so that this SCP point is centred in the finderscope by adjusting the altitude and orientation (east / west) of the tripod so that the finderscope points at the SCP.
10) Test your scope’s alignment by targeting an object, engage the RA motor (or manually find using RA axis only after a star has drifted off) and see if you have sorted out your alignment once and for all…..
11) Once you get to know where the SCP is you should be able to point the scope fairly quickly in future sessions.
See how you go, if in doubt, do what works for you. Please forgive any errors I may have made.
Last edited by Screwdriverone; 26-02-2008 at 10:36 AM.
Just a small side note on this, using this method, I found two things that were quite interesting.
1) My drift was virtually eliminated. I spent over 30mins on Jupiter with absolutely NO corrections.
2) When pointing the scope towards SCP, the 168 deg south was right, but the Altitude setting which WAS set correctly for my house of 33 degrees latitude, ended up being 36 degrees when I got the SCP centred correctly.
Anyone have any ideas on this one? Perhaps an inaccurate Lat dial?
Good one Chris - it's very easy to hit sigma octans and thence the SCP a number of ways: basically noting that it is (almost) mid-point between Acrux and Achernar.
I find using the distinct little triangle of Apus and following a line from beta Apus through gamma Apus (the (just)brighter pair) up to pi1 and pi2 Apus: these 2 little stars appearing like a double surrounded by an "arch/semicircle" of 6 stars stand out very clearly (they're in your first image attach.)
The top 2 stars of this "arch/semicircle" - eta Apus and delta Octans point straight to sigma Octans if you extend the distance between them twice!
Having a green laser pointer on your scope makes it so darn easy to just hit this area visually with its' beam (no stooping whatsoever!) and then use your finder and main scope with illum. ret. to crack a pretty darn accurate polar alignment. (of course having aligned your laser with the finder and main scope first!)
Phew, I am you confirmed my thoughts on the Lat setting, I was thinking I had to compensate for something else.....like dementia.
Darryl, funny you should mention halfway between Archenar and Acrux, because when I was drawing the lines on the first picture it struck me that the middle of the line between Archenar and Alpha Centauri was very close to the SCP, although a little low of it. I was going to mention this in the post, but a short instruction already had become a page and a half!
Unfortunately I don't have an illuminated reticle or green laser pointer, but in finding the actual position of Sigma Octanis etc, I attached my 11x70 binos to the scope using an adapter bracket and that helped me zero in on the spot in a view I was familiar with. This also means that I can get a binocular view of most other objects I target with the GEM mount.
Maybe I will try to attach my camera to the binocular eyepieces and see what becomes of that one??
thanks for that chris - I was just looking around for this - you have done a great job - you should put it into a doc and ask a moderator/mike to save it in the articles section (in left tab) so everyone in future can easily find it
I'm new to this, but I do have an equatorial mount. I tried to find omega octanis without much success, so the way that I align mine (with pretty good success) is that I set the altitudeto as close as I can, and then aim 1 leg at approx 168 deg (much like chris). I then have the problem that I am based in Sydney, so even on clear nights like last friday, its still difficult to see the smaller stars. Instead, I find a bright object like mars, or something else about 30 deg above the horizon, and focus in on that star/planet. Then, depending on any drift noticed with observing Mars, I correct either the azimuth or altitude until there is no more drift. On Friday when I did this, a cloud passed over mars just after I aligned the scope, and when the sky cleared 15min later Mars was still in the same spot. I am aware that this is not the "correct" method, and that it is a hack. However, until I get better at this, I think it works.
as an aside, having done this I was able to find other stellar objects by setting RA and DEC to the appropriate locations.
I will have to try your method though Chris, it sounds pretty comprehensive
Thanks to Mike and everyone for the kind words and for loading this up as a How To guide.
To Jshad84: It sounds like you have mastered the Dark Art of Drift Alignment with your description of how you lined up Mars and adjusted from there. Take a look at Geoff Smith's excellent How To guide here Basics of Drift Alignment / Polar Alignment
for more information on this method. You may have already read it if you have become a Drift Alignment Jedi Master!!
This is what I was using after my initial post that Geoff replied to and it is very comprehensive. However, I have been a little impatient as my clear sky time and my brain clarity time have been very limited and I ended up in a dreadful mess so I thought there might be another way.
As Master Yoda once said "Do or do not, there is no try"
and as I had tried and had come to the Do Not stage, I had to find another solution.
Well done J, I am sure your robe and light saber are on their way in the mail.
Last edited by Screwdriverone; 27-02-2008 at 07:24 PM.
Thanks Chris for your wonderful article.
I recently started prime focus photography with my 3" refractor on a motorised GSO equatorial mount. I found drift alignment quite frustrating and time consuming. If I purchase a polar axis finderscope( a was told a 20x4) and use your method do you think it will work?
Yes, there shouldnt be any reason why it wouldnt work, however, I am a bit confused when you say a 20X4 finderscope which is polar axis. Your GSO motorised equatorial mount is what is needed to line up to the SCP. Set your Altitude to your Latitude as in the article and line it all up using the instructions. The finderscope should be attached to the scope along the same line as the main scope so this will help with finding the stars shown in the diagrams.
Once the Altitude is set correctly, future sessions will only involve rotation in the clockwise direction if you are using the same position as previous nights.