Can someone please teach me how to use an EQ mount properly?
Hey guys and girls,
I have a German-type EQ mount. I've balanced the scope in the declination and right ascension axes through setting the counterweight position appropriately. I understand that the right-ascension axis has to be set to my latitude.
What I don't understand are the dials (marked 0-23 on the RA axis and every 10 degrees on the DE axis) on both axes. Especially the fact that the RA axis dial can be moved around...
So the idea is...
Set up mount and scope.
Aim RA axis to south pole (not magnetic south).
Set RA axis to latitude.
Then ???
I understand that objects can be pinpointed by RA/DE - but I also don't understand in stellarium what the different references are... you have
RA/DE (J2000)
RA/DE (of date)
Hour angle/DE
I know this is an ultra-noob topic - but I searched and couldn't find anything comprehensive as a thread...
If someone can please guide me through the rest of the steps and how to use the EQ mount appropriately, that'd be great!
My suggestion would be not to pay any attention to the markings. They are designed for finding objects in the sky based on Dec and RA. You are much better off finding your targets visually through star hopping.
... What I don't understand are the dials (marked 0-23 on the RA axis and every 10 degrees on the DE axis) on both axes. Especially the fact that the RA axis dial can be moved around...
You point the scope at an object with known RA and then rotate the dial so the index mark matches the RA of the object. As long as you don't physically move the mount, the dial will rotate with the RA axis and stay correct.
Quote:
... I understand that objects can be pinpointed by RA/DE - but I also don't understand in stellarium what the different references are... you have
RA/DE (J2000)
RA/DE (of date)
RA changes over time for reasons related to the earths orbit and polar inclination. While you are getting started the difference between J2000 and other recent epochs is hardly worth worrying about.
Getting your GEM aligned both quickly and accurately is not something you learn overnight. Go along to a viewing night and the old hands will be happy to show you the tricks of the trade.
My suggestion would be not to pay any attention to the markings. They are designed for finding objects in the sky based on Dec and RA. You are much better off finding your targets visually through star hopping.
I believe the knowledge of how to use the settingcircles provided on mounts is essential for understand the basics of celestial geometry..
just like the knowledge of how to add and subtract without the help pocket calculator.... You dont do it every time but it good to know what it means.
BTW, on EQ6 (from Sinta) the design of RA setting circle (Hour angle actually) is not good because it is coupled with driving motor.. It is meaningful only if you do not use slewing (in which case it can represent RA).
But if you slew, then the hour circle must be re-adjusted again according to the target object.
This may be the reason why people do not use them because the whole issue may be highly confusing to the novices.
I believe the knowledge of how to use the settingcircles provided on mounts is essential for understand the basics of celestial geometry..
just like the knowledge of how to add and subtract without the help pocket calculator.... You dont do it every time but it good to know what it means.
No denying that! My thinking is that when you are starting off you are better concentrating on what you need to start looking at objects and getting that WOW factor going. Getting bogged down in the finer details just may push beginners into the 'it's all too hard' frame of mind. Knowing the Dec and RA of an object is not essetnial to finding and viewing it...
The RA setting circle is of little use to a beginner on most mounts. It has two scales one for RA and one for Sidereal time. The idea is that you set the sidereal scale so that your current sidereal time is aligned to the meridian (straight up). Then the other scale will read the RA of the object.
If the setting circle could be made to follow sidereal time you could set your RA from the other scale. However the settingcircles usually move with the RA so all you can do easily is read the sidereal time of the object you have set the scale to.
The Dec scale is slightly easier to read but it also has two scale reference points When one is set to 90 deg the other will read the declination. On the whole it is rather messy unless you have pecision scales and vernier controls that allow you to set and read to at least an arc minute.
Mine (standard EQ6) has only one scale/ring on hour axis, and it is coupled with worm gear... so it is confusing for novices, and actually quite useless (especially if telescope is coupled with PC). But I was using them couple of times... sometimes it is just too much to bring the wole gear out, including computer and what'snot..
The "proper" mounts (like this Zeiss refractor on Zgb Observatory, where I spend some of my best years) have hour angle circle only (this particular mount has circles 0.5 metres in dia).
So hour angle had to be calculated from RA for particular local time if we wanted to use circles for aiming at objects.
Quote:
Originally Posted by Barrykgerdes
It has two scales one for RA and one for Sidereal time.
I have three EQ mounts of different types they all have two sets of numbers on the setting circle. However one set is just the inverse of the other and one set of numbers could also be used but will invlove a little more calculation. The esential thing to remember is that the observable position of a given RA is a function of Hour angle and local sidereal time
Hour angle = LST - Right ascension
Note that Hour angle and RA are measured in opposite directions at the equator. This is why there are two scales. One the inverse of the other.
However the easiest way to use the scale is to set the one that increases towards the east with the sidereal time at the meridian and read the RA off the other. If there is only one scale you will need to subtract on of the readings from 24.
Barry,
If you were right, then the there would have been two independently movable scales on two separate circles.. and there is only one.
However, the problem is the design:
Hour angle scale should be coupled with tracking motor (to act as sort of sideral clock), while slewing should be done with the separate motor which moves both the scale and axle. This would significantly complicate the design, though..
BTW, sideral time is hour angle of the ascending node of the Earth orbit (or equinox point in Aries).. but this is not the reason for two sets of numbers on RA/H scale, however this may look convenient at the first glance. I believe the inverse numbers on Hour/RA circle are simply because the mount is sold on both hemispheres.
Similar design issue is with polar finder and totally useless scales associated with it- I have seen some spooky methods to calculate the position angle of the Polaris or SCP.. and I never managed to understand it. The much easier way is just to have a look at CdC.. or to do drift adjustment, or just use the build-in reticle.
I'll second not bothering with the settingcircles , just line up on brightish object near what you want to got to and "star hop" is the most time effective way.
But, if you want to find something via the settingcircles , that's not hard either , just you need to use a torch to read them .... kills the night vision .... all you need to is get the mount reasonably well leveled and polar aligned, then point the scope at a bright star who's RA and Dec you know, dial up turn the RA drive on and dialup the star's RA and Dec, this is your starting point, then slew to the RA and Dec or the object you want to get to , if you've a low power ep in , the object should be in field of view (may not be centred but that's neither here nor there).
If it's not, then the mount is either not level and or not properly PA) , so choose another star nearer the object and repeat the process.
Most stellar objects wont move that far in the sky between epochs (ie 1950 to 2000) so I wouldn't worry about insignificant drifts over the years , just use J2000.
I've used this approach too.
I've never bothered with calculating the hour angle. Being lazy I just use base stars and keep the RA drive on.
I'll second not bothering with the settingcircles , just line up on brightish object near what you want to got to and "star hop" is the most time effective way.
But, if you want to find something via the settingcircles , that's not hard either , just you need to use a torch to read them .... kills the night vision .... all you need to is get the mount reasonably well leveled and polar aligned, then point the scope at a bright star who's RA and Dec you know, dial up turn the RA drive on and dialup the star's RA and Dec, this is your starting point, then slew to the RA and Dec or the object you want to get to , if you've a low power ep in , the object should be in field of view (may not be centred but that's neither here nor there).
If it's not, then the mount is either not level and or not properly PA) , so choose another star nearer the object and repeat the process.
Most stellar objects wont move that far in the sky between epochs (ie 1950 to 2000) so I wouldn't worry about insignificant drifts over the years , just use J2000.
I've used this approach too.
I've never bothered with calculating the hour angle. Being lazy I just use base stars and keep the RA drive on.
Spot on Ian, that's what I used to do with my old 10". If the circles are fairly large and finely graduated, this process works very well. If the object isn't exactly in the centre of the FOV it's not far away. Having a look around the object's neighbourhood quite often turns up other objects as well as the target. Having a bright star fairly close to the target makes the process more accurate.
Can someone please teach me how to use an EQ mount properly?
