Left: A telescope on an altazimuth mount, like this popular Dobsonian design, simply moves up-down and left-right. Right: A telescope on an equatorial mount moves in the directions of celestial north-south and east-west. This makes it easier to follow the moving stars as the Earth turns, and it can also help you stay oriented when you use a star chart at the eyepiece.

Sky & Telescope diagram.

For those of us in the Northern Hemisphere, the stars appear to pivot around a point in the sky very near Polaris, the North Star. An equatorial (“EQ”) mount has one of its two axes aimed toward that point, and that allows you to follow a star or planet in your telescope’s eyepiece with just a single east-to-west motion. Add a small motor, and the telescope will track the stars automatically.

In contrast, telescopes equipped with altitude-azimuth (“alt-az”) mounts, including Dobsonian reflectors, require you to move your telescope with both up-down and left-right motions to accomplish the same thing.

When beginners first learn about mounts, they tend to conclude that they need an equatorial mount. Sure, these can be handy, but be aware they tend to be larger, heavier, and more expensive than a mechanically simpler alt-az mount. Also, you have to be prepared to spend some time learning how to use an equatorial mount — its motions aren’t quite as intuitive as those of an alt-az. An equatorial mount that’s been set up incorrectly (something I see all the time) is maddening to use and will actually hinder your tracking ability.