69 replies to this topic

[Rinaldo]

Not sure if this is worthy for the How To section, figured I'd post it here. I encourage others to throw in their 2 cents as far as techniques...

I learned how to find deep sky objects by way of star hopping. Lying in my snow covered backyard next to my DS-10, flashlight in hand along with my copy of Astronomy magazine opened to the constellation of the month page, I would patiently compare star fields and triangulate landmarks in the sky in an attempt to find my target. Some nights I would walk inside empty handed, but on those other nights it was so rewarding when you finally got that object you were looking for! The good news was that once I tracked down an object, it was much easier to find it again. Before long, I had a list of objects I could easily find. After viewing them, I would always go for something new.

Anyway, I know a lot of people use GOTO and digital setting circles these days. At first I thought it was kinda cheesy, but then I realized maybe I was starting to sound "old." Geeze, I'm only 34, so I decided not to be completely against technology that allows people to enjoy the sights of the universe without what I feel is the rewarding challenge, or frustration for some, of finding the objects yourself. However, I still never recommend these scopes to beginners. What can I say, I’m biased.

If you are a beginner that can't afford GOTO/digital setting circles, and star hopping is a bit frustrating/intimidating, you can always use those compass looking thingy's printed on your mount. These are called setting circles, and they do pretty much the same thing as any computer mount does. The main difference is that you have to push the scope with your hand, you really don't need batteries, and you likely to become more familiar with the sky when picking out deep sky objects from star charts - which is your database of objects.

The only item you really need in order to use setting circles is a star chart or book of objects with their coordinates. Here are the basic steps, each of which will be followed by a more in depth explanation:

1. Level the mount while facing it north.
2. Perform a polar alignment.
3. Choose a bright star you are familiar with and look up its coordinates.
4. Point your telescope at the star and center it in the eyepiece.
5. Loosen the setscrews on both the R.A. and DEC circles so they can be rotated without moving the scope.
6. Make sure the star is still centered, and then rotate each setting circle to the stars coordinates.
7. Tighten the setscrews.
8. Look up the coordinates to your favorite objects and point away!

Make sure your mount is as level as possible. My GM-8 has two bubble levels built in. If yours does not, you can buy a portable one, or use your best guess. The more level your mount is, the more accurate your setting circles will be.

Take your time and perform an accurate polar alignment. Best results occur when you have a polar alignment scope. If your polar alignment scope has lines and stars printed on the glass, they should help you get a very accurate polar alignment within a couple of minutes. Just follow the instructions that came with the scope. If you do not have an alignment scope, place your eye close to the polar axis and adjust it best you can by eye.

Now pick a bright star and look up its coordinates. If you are not familiar with the coordinate system, it basically breaks down as follows:

Every object charted in the sky has a declination (DEC) measured in degrees, and this will go in your declination circle. Each degree is 60 minutes, so half a degree is written as 30’ or 30m. Each minute is broken down into seconds, and half a minute is expressed as 30” or 30s.

An objects right ascension (RA) breaks down into hours instead of degrees, which is then broken down into minutes and seconds as well. This goes in your right ascension circle.

So lets look up a star and set the declination circle. Once you set up the declination circle accurately with a level mount that is polar aligned, you never need to touch it again. Since its summer, lets use that nice juicy bluish star in Lyra known as Vega. Its DEC is 38d 41m 26s, above the celestial equator. Point your scope at Vega, and center it in the field of view. Once you get it centered, boost up the magnification and re-center it. This will help with accuracy.

After you center Vega, loosen the setscrew tension on your declination circle so you can rotate it to 38d 41m 26s without moving the telescope. Keeping a little bit of tension in the setscrew will help you adjust them. Ok, lets be realistic here, many setting circles don’t have enough increments to accommodate such an accurate setting down to the seconds, let alone minutes. My GM-8’s setting circles have a disappointing 2-degree increment spacing. So in this case I just place the circle a hair past 38 degrees. If you are half a degree off when searching for a target, it should be no biggie cause your lowest power eyepiece is hopefully over 1.5 degrees true field of view. Take your time and be accurate as possible. After you set the circle just past 38 degrees, double check to make sure your star is perfectly centered in the eyepiece.

Wait a minute, how do I know if my declination circle is on –38 or +38 degrees??? Simple. Pivot the telescope down toward the southern horizon a bit along the declination axis. Since you are moving it toward the south and are pointing closer to the celestial equator, the numbers will decrease. If they increase, then loosen your setting circle and turn it to the 38 on the other side of 0 degrees.

Now that you have the declination set, adjust the right ascension setting circle to 18h 33m 33.1s, which is Vega’s R.A. When adjusting the set screw on R.A, it’s a good idea to leave in a little bit of tension. The R.A. circle will remain accurate as long as you have your drive tracking. Once you power it off, you will have to set the R.A. again at the beginning of your next observing session. Leaving a slight bit of tension in the set screw will allow you to rotate the setting circle without needing tools, but also allow enough friction for the drive to keep the R.A. accurate for the entire observing session. Finding objects without use of the R.A. circle is done fairly easily as well, more on that later.

Now that you have your circles set, you should be able to dial in any objects coordinates in the sky. Try a few bright stars first, and always use a low power eyepiece that gives you a big TFOV. After successfully dialing in some bright stars, start looking for some deep sky objects. Try dialing in M13 globular star cluster in Hercules, then go for M11 open cluster in Scutum. Whenever you dial in an object, take several minutes and note with your naked eye where in the sky your telescope is pointing. Slowly memorize what stars are in the area. On future evenings, see if you can identify those stars by naked eye, then point your scope in that general direction. When you go to dial in the object on your setting circles, you will begin to find that your skill at pointing the scope by way of star hopping will improve.

Setting circles can be used without electric power driving the R.A. All you need is to have a general idea where an object is in the sky. Point the scope within the constellation that is home to your object of interest. Now dial in the objects declination. Once dialed in, slowly push the scope along the R.A. axis by hand while looking through a low power eyepiece. Eventually the object you are looking for will pass through the FOV. If it doesn’t, pan the telescope in the other direction. If after that you still can’t find it, double check the declination to make sure you didn’t accidentally nudge the scope.

Setting circles offer a good way of finding elusive deep sky objects. I often teach my friends how to find objects without the use of the R.A. circle. It is a good way to mix in constellation identification, chart usage, and an intro to star hopping that is less intimidating.

[Rammysherriff]

Nicely written - very helpful to those who don't know, and a refresher for peope like me who think they do.

[BluewaterObserva]

I used to have lists and lists of known offsets from bright stars too. Makes it more accurate is all. I recently looked for that list, and could not find it. So if anybody else has such lists and/or knows a link to some, I'd love to get at least some of them back again if possible.

[GUNER]

Rinaldo,
THANK-YOU!
I have been having trouble getting my DSC to work. Something is wrong with the set up. I spent some nights trying to star hop but just couldn't "get it".
I finally sort of figured out the setting circles. The first night I found M13/M92 & even M57 from my very light polluted site. The second time I tried I did something wrong & couldn't find anything. I couldn't figure out what I was doing wrong but now I have your post to use as a guide. I copied it to a word doc so I can take it with me if I ever get another clear nite here.
I used to agree with what you said about using GOTO or DSC. I thought I should learn how to find things without the aids first. What changed my thinking was something funny that a "old" amateur astronomer told me when I went to NEAF.
I talked to him about my scope & he asked how I liked the DSC. I told him I hadn't starting using them because I wanted to find DSO with them but with many nights without finding anything. He said "That's one way to go about it. Hey are you busy. I need a little help. I want to go have a smoke but it takes so long to get a fire going rubbing those two sticks together..maybe you could help me."

[GUNER]

Hi All,
Here are some of the lists for Ra/Dec that I use with my setting circles. Thought it might help. If there is someone who has trouble with the zipped file PM me & I could e-mail them to you.

Attached Files

•  156947-RA DEC LISTS.zip   648.3KB   1028 downloads

[Rinaldo]

Rinaldo,
THANK-YOU!


...but it takes so long to get a fire going rubbing those two sticks together..maybe you could help me."

Yea I see that side of the coin as well. I usually advise people who have GOTO/DSC to at least try to find 2 or 3 objects on their own (assuming they are interested in seeing the night sky), then the rest of the night use what hey invested in. I'm at the point though where if I know where an object is, I can find it equal or faster than someone using DSC. If its something new it takes a bit longer of course

[Tom L]

What an excellent post! We need to get Kevin to pin this to the top of the forum.

Well done, Rinaldo!

[Rammysherriff]

Yes, seconded. Pin it to the top please!

NB - a slight helpful hint from me whose setting circles are not too bad but not the worst out there:

if you have problems hitting your target, centre on a nearby known star, and see if it is necessary to reset the circles to its coordinates, then retry your target. It removes a little inaccuracy I think.

[Greg K.]

It's like driving a stick shift vs. an automatic. The automatic is easier but you're a little more detached from the driving experience.

Of course, I'm upgrading to GOTO now, and I drive an automatic car so I'm probably not one to talk..

[Echo]

Greg,
Great analogy, but I'm on the flip side of the coin! I always buy cars with stick shifts and will never give up my GOTO.

[Bill Grass]

Excellent post, Rinaldo!! I use my mount's setting circles all the time, and my method is pretty much identical to yours.

I agree...this should be a sticky!

[desertstars]

Setting circles demystified! Nice job!

[Rinaldo]

Thanks people, glad it is of use to some of ya!

[b1gred]

I'm the same way. I teach flying in basic airplanes, I drive a stick, but when it comes to scopes I'm a GOTO boy all the way. HOWEVER, it's real nice to be able to look at a star atlas, determing the RA/DEC and put those into your GOTO scope and have it GO TO them... Lots of fun.

[Rinaldo]

I'm the same way. I teach flying in basic airplanes... :

HAHA... if I had the choice between a Warrior/172 with a glass cockpit or analog gauges, I would definitely choose glass! I'd still shoot some approaches on the standby's every once in a while though.

[KenF9000]

Excellent article - I found M57 a few weeks ago just by pointing the scope in the general area - more by good luck than by knowledge - last time I tried - could not find it.

I'm now going to give those setting circles a try - I may just provide the solution I need - whilst I workout how to fix some Meade4504 drives and handset to the mount...

[werewolf6977]

Rinaldo: I've got "setting circles"(?) on my SP130EQ. After reading your article, I'm gonna have to give'em a try. One thing though, I can't find anyway to loosen the Dec circle on my eq-2 mount. Am I overlooking something? I don't see a set screw for that one. there is one on the RA axis, but not the Dec. Pete

[Rinaldo]

Pete, it may have been factory calibrated already. Use the technique above on a bright star and see. If not, then check and see if it can be turned by hand. Perhaps they have it so it works off of friction? -thus not needing a set screw. Try my first suggestion though so you don't accidently "fix somthin that ain't broke!"

[KenF9000]

After reading much in these forums, particularly those on the use of setting circles, polar alignment. I eventually managed to put them in action (1st good clear night for ages).

I spent about 20 minutes setting the scope up for polar. Leveled the scope first - set the RA circles to the correct date and time for polar alignment - then looked through the polar scope - not bad - Polaris was in view but not in the small circle - turned the Alt-Az screws - got it almost spot on.

I then moved the scope (no drives as yet) to a star of known RA and Dec - set the RA accordingly and checked the DEC. Next - push the scope to another star of known RA and DEC - check the values - Excellent - nearly spot on.

1st Target - Find M81 - So visually located Alpha Ursa Major - checked the DEC and RA - adjusted slightly to set it accurately then pushed to where M81 should be - looked through my 32mm - what's that fuzzy near center - Oh must be M81 - well I never. It works. Hang on what's that other bit of fuzz. Must be M82 - Yep.

I spent the next 30 minutes just staring at these two - absolutely wonderful.

Next challenge - M57, pre-aligned to Gamma Lyra reset the RA, then pushed to M57 co-ords - there she was.

The point is - for those of you who have scopes with no goto - align your scope and use those setting circles. It really does work.

[Chris Graham]

I'm still having a problem with this

Am i just thick or something?

If you set your scope up right (which i'm sure i'm doing) and say you point it to Vega which is RA 18 and a bit surely this shall have to be re adjusted due to moving to different objects if you dont keep them in center of the view.

Also i'm having problems tracking an object, can u do this with just RA?

Any help would be great.

[dgs©]

If you have a motor drive operating at the correct speed the RA numbers should stay correct as long as the drive is not turned off.
Just to be sure, I always do my 'hops' in pairs... starting with a known object, I make sure the setting circles are set to the correct numbers, then turn to the new numbers. Often I don't have to adjust at the starting point if it is what I have been observing, but sometimes I do.
Tracking should require only the RA to turn. If not tracking then the motor speed is incorrect (low batteries?) or the polar alignment is not good, or both.
Make certain alignment is good and the mount is level.

[KenF9000]

Xenoaxle - check to make sure your RA scale lock is not screwed down otherwise as you move in RA the scale may not move with you. You lock it initially to get the pole star aligned - make sure you unlock and leave it unlocked when you scope about.

Clear Skies - soon I hope.

[Cerberus]

People should have to prove they can locate object on thier own before they are allowed to buy a Goto mount. I consider it cheating. It can be a challenged how ever, to get good at dead-reconing with an EQ.