Setting Circles

[Ed in UK]

Hi Everyone,

With my confidence riding perhaps higher than it should have after done watching Jupiter and Mars yesterday morning, I decided to raise the bar a little and go after Uranus last night.

Here in Lincolnshire  (UK) I can't see the planet and spent Saturday night outside for a quite a while along with a set of bins and Stellarium to familiarise myself with that area of the sky.

Discovered Aries and found Pegasus but I really struggled to see anything of Picies.

Last night I got the scope out, polar aligned it, used Aldebaran to calibrate the RA setting circle (4H 33Mins ) then dialed in the settings for Uranus from Stellarium and bingo didn't recognise a thing.

Couldn't find anything through the scope that resembled what I could see on Stellarium. I eventually twigged that I seemed to be about 15 to 20 degrees out to the west. ?

Even when taking into account my error still couldn't find anything in the scope that matched Stellarium.

Any ideas please as to what may have caused this error ?

Doubled checked the RA setting tonight and it's still on 4H 33Mins that I set for Aldebaran.

Not so worried about not matching what I see in the Scope to Stellarium but do need to know where I went wrong with the setting circles.

Many thanks in advance.

Ed

[Merlin66]

What about Dec settings?

If you had Aldebaran at -16 deg rather than +16 deg you'd get that type of error????

 

[LukeSkywatcher]

In my opinion, setting circles on a scope mount are there for decoration. If its an EQ mount you have, the RA and Dec controls are all you need.

[Merlin66]

Luke,

in the good old days setting circles were used to find and identify objects.

on my 12” scope I had 350mm diameter circles with a 1/4 degree accuracy.

I do agree that the current mini versions found on the current mounts are far from easy to use, but within limits will still work.

 

[Astro Imp]

I know setting circles get a lot of bad press but when I started with an EQ3-2 I used them fairly successfully but it was a bit of a fiddle. 

[Ed in UK]

Thanks all for your feedback.

Merlin66 -  the instructions with the scope say that that Dec Setting was factory set and therefore no calibration required, but if there was an error on Dec I would see that has a North/South misalignment not an East/West ?

I'm confident it's finger trouble on my part, after all it was my first attempt at this.

I wasn't sure if there was something I forgot to factor in, if I set the scope to RA 4H 33Mins on Aldebaran give it say 10 mins of time to pass although the scope remains set on 4H 33Mins its no longer pointing at Aldebaran due to earths rotation if you see what I mean.

Certainly need to do more research and try again.

Not expecting pin point results, just would be great to get to a approx area that I can use as a starting point.

Thanks 

Ed

[tuckstar]

The smaller the setting circle the larger the margin for error. I use a setting circle on my dob, yeah I know it's alt az, which is nearly the same diameter of my base and this works quite well.

[Ed in UK]

34 minutes ago, tuckstar said:

The smaller the setting circle the larger the margin for error. I use a setting circle on my dob, yeah I know it's alt az, which is nearly the same diameter of my base and this works quite well.

Totally understand but such a large error is more that just misalignment with the scale calibrated in 10mins segments.

[Merlin66]

Ed,

You didn't say which direction the error was in the OP......

The RA of the target star will not change. The RA circle rotates with the axis so that the reading for the star moves with the star as the Earth rotates.

(What changes is the Hour Angle. This is the local Sidereal time (the RA of the meridian) - RA of the star)

[Ed in UK]

Thanks Merlin.

The Dec looked as if the scope elevated to roughly the right height.

However with RA if it should have been due south it faced/pointed SSW approx.

Watched a few video's on You Tube so will practice again next clear night.

[LukeSkywatcher]

Setting circles are a remnant of telescopes gone by. Useful once, but no longer. I see them a bit like the coccyx (tail bone in modern humans) and the appendix.. Useful at one time in evolution... but redundant now.

[25585]

Readable setting circles are rare, but the general use is still applicable if you are looking using RA & Dec co-ordinates read from a data list or star atlas grid (Uranometria & Sky Atlas 2000 have overlay grids). 

However polar alignment is crucial, which is where most errors occur. The RA & Dec must be locked at right angles to each other, then the mount must be aligned to Polaris in alt & azi only, then those locked. 

After that, unlocking RA & dec & using the circles should get you to near or very near the co-ordinates you have moved to. But finder scope & wide FOV eye piece are still needed to centre your object. 

Finding something in a group or cluster, especially closed in, is in my experience not often possible just using the processes above. But once whatever you want is found, you only have to track or catch-up in one axis.