Surface Brightness Calculator

What This Calculator Tells You

Surface brightness measures how much light is spread over an object's apparent area. Unlike integrated magnitude (total brightness), surface brightness tells you how detectable an extended object will be - a large, faint galaxy may be harder to see than a smaller, more compact object of the same integrated magnitude.

Example Objects

Object sizes are approximate and depend on how faint outer regions are defined; values shown represent commonly used visual extents.

Understanding Surface Brightness

• Lower numbers = brighter: Like magnitude, smaller surface brightness means more light per area
• Sky background is ~21.5-22 mag/arcsec²: Objects fainter than the sky background are very difficult
• Magnification doesn't help (much): Higher power spreads both object AND sky background, keeping contrast roughly constant
• Aperture increases signal: Magnification mainly affects exit pupil and image scale

Observation Tips

• For low surface brightness: Use low power to keep the exit pupil large (5-7mm) and the sky background dark
• UHC or OIII filters: Can dramatically improve nebula visibility by increasing contrast
• Dark adaptation: Full dark adaptation (30+ minutes) is crucial for faint extended objects
• Averted vision: Looking slightly away uses more sensitive rod cells

Related Calculators

• Limiting Magnitude Calculator - For point sources like stars
• Apparent vs Absolute Magnitude - Intrinsic vs observed brightness