# Difficulty rating

Also called: easy, moderate, challenging, very hard, out of reach, visibility.

How hard an object is tonight — easy, moderate, challenging, very hard or out of reach — for your sky, instrument and Moon.

AstroPilot works out how much an object stands out from the sky background at its best moment tonight, using its [surface brightness](https://astropilot.space/glossary/surface-brightness) and size, your sky's darkness ([bortle scale](https://astropilot.space/glossary/bortle-scale)), your instrument's [aperture](https://astropilot.space/glossary/aperture), the [moonlight](https://astropilot.space/glossary/moonlight) and [extinction](https://astropilot.space/glossary/extinction) at its altitude — following how the eye detects faint light. Easy objects show at a glance; challenging ones need [averted vision](https://astropilot.space/glossary/averted-vision) and patience.

**In AstroPilot:** Every object card and page; Explore ranks objects by it.

**Related:** [Surface brightness](https://astropilot.space/glossary/surface-brightness.md), [Bortle scale](https://astropilot.space/glossary/bortle-scale.md), [Averted vision](https://astropilot.space/glossary/averted-vision.md), [Moonlight](https://astropilot.space/glossary/moonlight.md)

From the AstroPilot astronomy glossary: https://astropilot.space/glossary/difficulty