Feel really dumb asking this......

[keef_uk]

...but after a year or so of just looking up and gazing (I mainly do lunar scoping) I still dont get that meaning of:

RA/DE: 10h17m35s/+12o33'01"

I know its means Right Ascension and Declination and I have seen these setting circles on my mount but are they like co-ordinates in the sky and if so how do I set? Can someone give me an idiots guide or point me to a straight forward talking website?

Cheers

[themos]

Yes, they are coordinates in the sky. The Declination tells you the angle to Polaris (except +90 degrees corresponds to Polaris and 0 to a point 90 degrees from Polaris and -90 to a point opposite Polaris). The Right Ascension tells you how much later a star will cross the southern meridian ( after whatever is on the 0h0m0s position).

[barkis]

The Right Ascension or Hours Minutes and seconds apply to every object in the sky, as do the declination, which is in degrees, minutes and seconds. They change only in respect of Planets, the Moon, and the sun, because those bodies have a motion of their own that are discernible.

The stars and galaxies also change, but their coordinates are altered on star maps every epoch, which are in 50 year time scales. To all intents and purpose, stars and extra galactic objects stay the same.

If your mount is a permanent one, then once you have set the declination to that of a known star, and lock it, it should need no further adjustment, as declination of galactic objects are fixed also for a particular epoch. Only the Sun, planets, and moons declination changes, on a daily basis, or even on an hourly basis.

Just to add. The Celestial equator is merely the earths equator projected out into space. On the declination scale that is represented by Zero degrees. Any object north of the equator is termed + but the positive sign is not always used, whereas any object south of the equator is marked as - degrees.

South declination objects will always be marked as negative degrees on star maps or charts.

Ron.

[MikeP]

Have a look at this site. It illustrates RA/Dec, Alt/Az, zenith, hour angle etc etc in simple diagrams.

http://www.physics.csbsju.edu/astro/CS/CSintro.html

Mike

[keef_uk]

Thanks for your replies - but even more basic gthen that is how do I use this infor with my CG3 mount to find objects in the sky?

[scotastro]

Keef

The simplest way of thinking of RA and Dec is the same as latitude and longitude on Earth. Except we measure RA as time rather than in degrees. So just like every town or city has unique location co-ordinates so does any point in the night sky.

Sorry now for some bad news - your CG3 mount (and just about all other EQ mounts) has setting circle discs that are too small to have any degree of accuracy for locating object. To be of any real use they need to be at least twice the size.

However, try it and see. Here is a link to a brief description of how to use them http://www.ehow.com/how_18265_telescope-with-setting.html

Finding M13 from eta Hercules or M57 from Vega should just work as the distance the scope is moving is not too great. To ensure best accuracy you should always reset the RA and Dec circles on a new star before trying for a new DSO. Use your lowerst power EP to get the widest field of view.

The Sellarium free planetarium program will give you RA and Dec figures for all stars and DSOs.

This is not a new problem mounts have been made with tiny setting circles for more than 30 years and no, I don't know either why they do it.

Scotastro

[Ajohn]

There are several free good planetarium software packages about which to a certain extent along with the typical size of setting circles make the whole thing a bit pointless. The RA can be confusing because instead of specifying an angle in deg, min, sec it's in hours min and sec. Both mins are 1/60th of what ever and the secs are 1/60th of that. The RA wheel will also have a date scale. You may also come across the words hour angle.

The main use these day is setting up a polar alignment scope properly. The pole star isn't quite on the pole and also moves around it. so the RA axis has to be pointed slightly away from it. This means aligning the scope with the mount itself, loosening the dials and then setting a specific date and a time on the dials with the view through the polar scope in a certain orientation. There is usually a straight line which must be vertical. The dials can then be locked in position, the correct date and time set and the polar scope used to align the RA axis. Understanding just how the last bit is done though leaves me wondering if some of the people who wrote the instructions don't understand either.

Thought I should point out why even small ones are of some use.

John

[The Warthog]

I only use RA and Dec to get from a known object to an unknown nearby object. So, if I point at Vega, and want to see the Ring Nebula, I calculate the difference between the RAs and Decs of the two objects, and move the scope the few degrees indicated by the differences. Using a low power ep, this usually works very well, as the markings on my EQ3-2 mount are adequate to put the target somewhere in the FOV.

[Talitha]

Here's the simplest way I can explain it, Keith. You point the scope at a known star and use that star's co-ordinates to calibrate the setting circles. Assuming the scope is level and properly polarized, you should then be able to 'dial in' any given target by rotating the RA and Dec of the scope to the new target's co-ordinates, using the readings on the setting circles as guides.

I'm not sure if your mount has a driven or non-driven RA circle. The RA circle on my 1st scope (ETX 90RA) was non-driven, and I needed to re-calibrate it from target-to-target. In other words, after I got through observing an object, I'd use that object's co-ordinates to re-calibrate the RA circle, which would then enable me to dial in my next target.

But the RA circle on my LX-10 is driven (tracks right along with the worm gear), so I only need to calibrate it at the beginning of the session.