Birchardville Observatory
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What is an Equatorial Platform?

The [very basic] Background

The stars move across our sky because the world on which we stand rotates once each day. Actually, on a solar basis, the earth revolves on its axis, on average, once every 1440 minutes. We're generally looking at stars and deep space objects, and based on stellar objects, the rotation is just a bit faster - once every 1436 minutes.

My telescopes do not have clock driven mounts, that is, they are fixed with respect to the earth. To follow a celestial object across the sky, the observer has to keep pushing or pulling the telescope to try to keep the object within the telescope's field of view. As magnification increases, this becomes more difficult. Of course, a long term study of Polaris would not be impacted very much by this effect, but the Great Nebula (M42) in Orion is near the equator and greatly affected.

So, now we all agree that "Something MUST be done!" But what?

  • Keep pushing and pulling -- cheap but not rewarding
  • Buy a good equatorial mount that can safely and precisely carry your telescope -- NOT cheap but gives good views
  • Make something! -- we always pretend this is cheap AND rewarding. This is the Equatorial Platform approach.

A bit more depth

Imagine along with me... Build a platform mounted on an axle that can be aligned parallel to the Earth's axis. Put a motor on the axle that causes it to rotate once every 1436 minutes when following stellar objects, and some similar rate for Solar System things. Set the telescope and its mount on this platform and, As The World Turns, the platform axle turns in the opposite direction to exactly compensate for the Earth's rotation.

The problems left involve support, building and aligning a rigid axle, and so on. There is a better way -- it's called an Equatorial Platform, and because of the scale of the parts, less intrinsic precision is needed (bearings are 10 or 20 or 30 inches in diameter, for example, so the needed tolerance is much less -- less enough that a reasonably equipped wood shop can do the needed work. (This same argument, applied differently, led John Dobson to the idea of inexpensive, home-made telescopes.)

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Contact Info:
Name:Dan Janda