Hard to get my head around

[freewheeler]

I have just acquired a Celestron AstroMaster 114 EQ telescope and after reading and re-reading the instruction book and various web articles I thought I had understood Dec and RA. My understanding led me to believe that adjusting DEC would be "Up & Down" and adjusting RA would be "Side to Side".

However the adjustments for DEC  move the scope side to side with the scope remaining on the same angular plane and the adjustments for RA  just swings the scope in an arc around the mount but leaving it pointing in the same direction.

I would appreciate it very much if anybody can help me get a better understanding.

[Dave Lloyd]

The RA axis points at the pole and revolves to simulate the movement of the star field as the Earth rotates on its axis. This is fixed. When this is set point your scope at what you're looking at. The declination will stay fixed relative to the RA axis while the RA axis plus telescope follows the object across the sky, either with a motor or slow motion controls.

[Cornelius Varley]

It might be better not to think about "side to side" and "up and down", these terms are more suitable for an alt-azimuth mount.. The RA axis rotates the telescope on the polar axis and the DEC rotates the telescope on the declination axis which is at 90° to the RA axis.

The sort equatorial mount tutorial shows how an equatorial moves around the sky.

[Riemann]

As the earth rotates the stars appear move around the axis that goes through the earth from celestial north (Polaris roughly) to celestial south.    For stars in the general region of Polaris, the stars describe circles in the sky - one star stays on a particular circle, and moves round it during the night..   For stars elsewhere in the sky they describe arcs in the sky , (the circles being completed below the horizon, i.e. round the back of the earth from where you are standing).    Again, any particular star will always live on that particular arc.

If you have your telescope mount properly aligned to celestial north then adjusting DEC moves you from one arc or circle to another arc or circle, i.e. from the path of one star onto the path of another star.    Adjusting RA takes you round that one particular arc or circle, and can be tied into the time of day.   So if you have the mount correctly aligned, once you have your target in view through the eyepiece you only need to use the fine RA adjustment knob to keep tracking it as it slowly moves across the sky.

How much RA moves the scope around the sky depends on the DEC setting.   With a DEC setting that points north or low south, RA does not move the scope much.    But use a DEC setting that has the scope point east, to the zenith (straight up) or to the west and you will see that RA will take you in a huge arc to different parts of the sky.

Hope that helps.

 

 

[Dave In Vermont]

Here's a youtube entry on using an equatorial-mount:

 

And many more can be found through a Google search (and others):

https://www.google.com/search?q=How+a+equatorial-mount+works+-+youtube&ie=utf-8&oe=utf-8

This should help. Let us know!

Enjoy -

Dave

 

 

[freewheeler]

Thank you all very much. Every post has been extremely helpful and I can now understand what is happening.