Backyard Astronomy Glossary: 15 Terms Explained
The words that show up in backyard astronomy specs, reviews and how-to guides, explained without jargon.
- Aperture
- The diameter of a telescope's main lens or mirror. It controls how much light is gathered and how much detail can be seen.
- Related: Best Dobsonian Telescopes for Deep-Sky Views (2026) →
- Barlow lens
- An accessory that multiplies an eyepiece's magnification, often by 2x.
- Related: Best Barlow Lenses to Boost Your Magnification (2026) →
- Collimation
- Aligning a reflector's mirrors. Poor collimation blurs views at high power.
- Related: Best Collimators for Razor-Sharp Optics (2026) →
- Dobsonian
- A reflector on a simple rocker box mount, the classic value choice for visual observing.
- Related: Best Dobsonian Telescopes for Deep-Sky Views (2026) →
- Equatorial mount
- A mount aligned with Earth's axis so objects can be tracked with one motion.
- Related: Best Equatorial Mounts for Tracking the Sky (2026) →
- Focal length
- The distance light travels to focus. Divide the telescope's focal length by the eyepiece's to get magnification.
- Focal ratio
- Focal length divided by aperture, like f/5. Low ratios give wider views, high ratios suit planets.
- GoTo mount
- A computerized mount that finds and tracks objects automatically.
- Related: Best GoTo Mounts for Automated Object Finding (2026) →
- Intervalometer
- A remote timer that fires long exposures in sequence for astrophotography and star trails.
- Related: Best Intervalometers for Automated Astro Shots (2026) →
- Light pollution filter
- A filter that blocks some artificial light wavelengths to boost contrast on certain nebulae.
- Related: Best Light Pollution Filters for City Skies (2026) →
- Maksutov-Cassegrain
- A compact catadioptric telescope with long focal length, good for the Moon and planets.
- Related: Best Maksutov Telescopes for Planets and Moon (2026) →
- Reflector
- A telescope that uses mirrors, giving more aperture for the money.
- Related: Best Reflector Telescopes for Deep-Sky (2026) →
- Refractor
- A telescope that uses lenses. Low maintenance and sharp, but large apertures are expensive.
- Related: Best Refractor Telescopes for Sharp Views (2026) →
- Seeing
- Atmospheric steadiness. On unsteady nights high magnification looks blurry regardless of the telescope.
- Solar filter
- A certified filter that fits securely over the front of a telescope for safe Sun viewing. Never look at the Sun without one.
- Related: Best Solar Filters for Safe Sun Observing (2026) →