What telescope tracking means
The sky appears to move because the Earth rotates. At the eyepiece, this apparent motion is more noticeable the more you magnify: an object can leave the field of view in a minute or so at high power. Tracking is the telescope mount’s ability to turn at a steady rate that matches this motion, so your target stays in view without you nudging the telescope by hand.
Tracking is not the same as pointing. A mount can track without being able to find objects on its own, and a GoTo mount does both.
Why tracking matters
- Visual observing: it keeps planets and the Moon centered at high magnification, and lets you share the view with others without re-aiming.
- Astrophotography: long exposures require the telescope to follow the sky precisely, otherwise stars smear into trails.
- Comfort: you can spend your time looking rather than adjusting.
Types of tracking
Manual tracking
On a basic altazimuth mount, such as a Dobsonian or simple tripod, you push the telescope by hand to recenter the target every so often. Many observers find this perfectly pleasant at low to moderate power. Some Dobsonians can be placed on an equatorial platform that provides motorized tracking.
Equatorial tracking
An equatorial mount that has been polar aligned can follow the sky by turning about one axis, the right ascension axis, at a constant rate. A simple single-axis motor drive is often enough for visual use. This is why equatorial mounts are favored for imaging. For setup, see setting up a telescope with an equatorial mount.
Altazimuth motorized tracking
A computerized altazimuth mount must move both axes at changing speeds to follow the sky. Modern GoTo mounts do this smoothly. A downside for imaging is field rotation: over a long exposure the field slowly rotates around the target, which limits exposure length unless you use short exposures or a field derotator. For visual use it is rarely noticeable.
GoTo and smart telescopes
GoTo mounts have a database of objects and motors on both axes. After an alignment routine, they point at a chosen target and then track it. Smart telescopes go further by combining plate solving with an app. Features and prices vary widely by model, so check what a specific product actually does before buying.
Tracking rates
Mounts commonly offer several rates:
- Sidereal: the rate that follows the stars.
- Lunar: the Moon moves slightly differently against the stars.
- Solar: for the Sun, which is only to be observed with a proper solar filter; see using a telescope during the day.
If your Moon drifts slowly at sidereal rate, switching to lunar rate may help.
Tracking versus guiding
Tracking follows the nominal motion of the sky. Guiding goes a step further: a small camera watches a star and sends tiny corrections to the mount to cancel out errors such as imperfect gear teeth (periodic error) and slight alignment inaccuracies. Visual observers rarely need guiding. Imagers doing multi-minute exposures often do. Improving polar alignment reduces what the guider has to fix.
Why tracking may be poor
If your telescope drifts more than expected, possible causes include:
- Poor polar alignment on an equatorial mount.
- Poor balance, which strains the motor.
- Incorrect latitude, date, time or location settings on a GoTo mount.
- A flexing or unstable support, including a wobbly tripod; see the telescope pier guide for a stiffer option.
- Drive settings such as the wrong tracking rate.
- Low batteries, which can make motors behave erratically.
Getting started
If you are still new to using a telescope, our beginner guide to using a telescope is the best first stop. Tracking is a nice convenience, but many people enjoy years of observing with a manually pushed Dobsonian.
Choosing a mount for tracking
For visual use, a motorized altazimuth or a basic single-axis drive on an equatorial mount is usually enough. For imaging, a sturdy equatorial mount with a decent payload margin is typically recommended. Check the manufacturer’s stated payload and be conservative, because real-world performance usually falls short of the maximum rating.