Astronomy Hacks

Build or Buy an Equatorial Platform

The Dobsonian mount was a wonderful innovation.It’s simple, inexpensive, smooth, extremely stable, and intuitive to use. The only downside is that a Dob doesn’t track the motion of the stars. Or at least it doesn’t unless you put it on an equatorial platform.

An equatorial platform,or EQ platform for short, is a squat, flat, motor-driven table that sits underneath the Dob base and gradually pivots the scope at the exact rate needed to counteract the apparent motion of the stars. When you use an EQ platform, you continue to point the Dob normally, moving it in altitude and azimuth to locate objects. The difference is, when you stop moving the Dob, it begins tracking and the object in the eyepiece remains centered rather than drifting out of view as Earth rotates. Figure4-37 shows an EQ platform built by Steve Childers, underneath the rocker box of his 10” Orion XT10 Dob.

Figure 4-37. A typical equatorial platform

The equatorial platform pivots on the curved bearing shown in Figure 4-37, as well as a similar bearing at the far end of the platform, not visible in the figure. The bearing dimensions are calculated for the specific latitude at which the platform is to be used.

Using an EQ platform preserves all of the advantages of a Dob—large aperture; easy, intuitive motions, and so on—while adding all of the benefits of a driven equatorial mount. (Well, ...