Finding and Tracking Objects with an EQ Mount
Now that your equatorial mount is set up and aligned, you are ready to point it at objects and track them across the sky.
Finding objects you want to observe is one of the great challenges and satisfactions in amateur astronomy. (And the difficulty of finding objects is one of the surprises that sometimes disappoints beginners with unrealistic expectations.) Another article will cover the basic techniques used to find challenging objects, and yet another suggests some easy beginner targets. For now, let's assume that you want to point at something that you can actually see with the naked eye, like the planet Jupiter.
Beginners will often think "ok, I just swing the scope left until it's pointing in the correct direction, and up until I see Jupiter". That's exactly what you do with an Alt-Az mount, but an equatorial mount moves in unfamiliar directions: Right Ascension and Declination, not left/right and up/down. These unfamiliar directions are the reason many beginners are initially frustrated by equatorial mounts. You'll quickly get used to it, and the convenience you'll have once you are observing an object (below) is worth the complexity now.
The steps below apply to finding an object using a mount that does not have a go-to feature. (You can't move a go-to mount manually or it will lose track of the sky position. A separate article covers this.)
One more thing. What about the engraved circular scales on the Right Ascension and Declination axes of your mount? (These are called "setting circles".) On an inexpensive, entry-level mount: forget them, they are decorations, not useable tools. You'll learn another technique to find things. (Sorry.)
Now, let's practice pointing the telescope.
|We assume you have the mount assembled, polar aligned, the telescope securely mounted and properly balanced, and the finder scope aligned so they point accurately.|
|Let's also assume that your desired target (Jupiter) is in another part of the sky, not even close to where the telescope is currently pointing.|
| Loosen the clutches that prevent motion of the RA and Dec axes. Hold the telescope with one hand while doing this. Because you balanced the mount it should not flop to the side, but it's better to be safe here.
(Yes, that's me. Sorry I didn't dress more formally for the occasion.)
|Gently holding the scope, move the Declination axis about 1/4 to 1/2 of the way around in the direction of Jupiter.|
|Note that it's pointing 'way too high or too low in the sky.|
|Move the RA axis about 1/2 to 3/4 of the way in the direction that improves the pointing of the scope toward Jupiter.|
| Repeat this a couple of times - get the Declination direction closer, then the RA direction, etc. After a few times you will develop the knack of moving both of these directions smoothly, almost at the same time, to guide the scope into the right general area of the sky.
When you have the scope pointing approximately at your target, hold it with one hand and tighten the RA and Declination clutches again with the other hand.
|Now, look through your unit-power finder, or just sight along the tube of the telescope, and use the mount's flexible slow-motion controls (manual or electric) to continue moving toward the target, alternating between the RA and Declination adjustments.|
| If you have a unit-power "red dot" finder, keep going until the red dot is directly on the target. If you have a magnifying finder, switch to it and adjust until the target is centred in the cross hairs.
Finally, switch to the telescope, with a wide-angle eyepiece. Your target should be visible in the field of view. Further adjust the centering, then switch to a higher-power eyepiece if desired.
|If you have both a unit-power and a magnifying finder, you probably won't need the magnifying finder for an easy target like Jupiter which you can see with your naked eye. You'll reserve the magnifying finder for more challenging targets.|
Note that after you swing the telescope across a major portion of the sky, the eyepiece may end up on the other side of the telescope (this seemingly strange comment will be clear the first time it happens to you).
We'll fix that in a moment. However, this picture serves to remind us why it's important to tighten the set-screws holding the diagonal and eyepiece in place. If your eyepiece is just sitting in the diagonal and you move to a part of the sky where it is underneath, it can fall out. (Thanks to reader TerryC for suggesting this warning.)
|Loosen the diagonal in the focuser (for a refractor or an SCT), or loosen the rings holding the optical tube (for a newtonian reflector) and gently rotate it until the eyepiece is at a comfortable angle again, then re-tighten.|
A Few Extra Complexities
There are a couple of extra complexities of equatorial mounts. These are almost never a problem, but you will probably encounter them eventually, so I'll mention them here.
|First, note that the mount is not capable of making a complete circle in the Right Ascension direction - eventually the scope or some part of the mount bumps into the tripod.|
| Next, you'll eventually notice that the mount is capable of pointing at certain parts of the sky in two different ways.
For example, in this picture we are pointed toward the South, with the scope on the East side of the mount and the counterweight on the West side of the mount.
|while in this picture we are pointed to the same part of the sky, but the scope is on the West side of the mount and the counterweight is on the East.|
| This will just be a curiousity for a while. Eventually you'll find yourself in a situation where it is better to choose one side over the other. If you are planning to observe an object for a long time, you'll want to pick the side where the motion of tracking the object across the sky is not impeded by the scope bumping into the mount.
In a long observing session, you may even have to do a "meridian flip" - pausing from your observations and rotating the scope around to the other side of the mount to continue.
|This is more of an issue with motor-drive systems, or go-to systems, and long-exposure astrophotography, and will not likely affect a visual beginner.|
|The final complexity is that equatorial mounts have difficulty pointing at Polaris. Eventually you might want to look at Polaris, because it is famous and a binary star, and because, not moving, it is a good target for checking optics, aligning finders, etc.|
|A perfectly aligned equatorial mount should point at polaris by just moving the Declination axis until Polaris is centred - any position of the RA axis will work. However, since your mount is probably not perfectly aligned you will find you have to hunt through the entire range of RA looking for the elusive spot where Polaris is in view. This is why, if I'm going to use Polaris to align my finder, I tend to do it before polar-aligning my mount.|
|Once you have your target centred in the eyepiece, you are ready to appreciate the equatorial mount. As you observe for an extended period, you will note that your target drifts out of the field of view. Depending on the magnification, it may stay in the field for only one or two minutes.|
|With a properly aligned equatorial mount, you need only keep one hand on the RA slow motion control, and gently turning it will keep the target centred. (Argh, I forgot to take this picture. Eventually I will.)|
|Better still, if you have a motor drive on your RA axis, switch on the motor and the object will seem to stop drifting, remaining perfectly stable and centred in the field. The motor is turning the RA axis at the same rate as the Earth is rotating, and the whole point of polar aligning your mount was that this motion would cancel the motion of the stars.|
Over a long period (half an hour or more) you may notice your target gradually drifting. This indicates that your polar alignment wasn't perfect. Correcting this minor drift is what "drift alignment" is all about, but it is worthwhile effort only for long-exposure photography or permanently-mounted equipment.
|Back: Polar Align||
end of setup series
|Back to Astronomy Writings||Up to Richard's Astronomy Section||Back to Setting Up article|
|based on work of former commenterra||Recent comments|