One formula · your inputs
Dawes limit calculator
The Dawes relation is an empirical visual double-star estimate expressed as 116 divided by aperture in millimetres.
It is not a guaranteed observed resolution and does not include seeing, wavelength, contrast or optical quality.
Formula
How it is calculated
Dawes limit (arcseconds) ≈ 116 ÷ aperture (mm)- Enter clear aperture in millimetres.
- Divide the empirical constant 116 by that aperture.
- Keep the result as an estimate, not a pass/fail threshold.
What the result represents
The conventional empirical Dawes relation for visual double-star separation.
The page keeps every decision-bearing quantity visible as an input. It does not look up a product catalogue, current market value or hidden recommended preset.
Limits of the model
The result is an idealised optical or geometric estimate from user-entered values. It does not model seeing, optical quality, central obstruction, transmission, distortion, focus error, tracking or sensor calibration.
Use the number to compare transparent scenarios. Verify critical observations, equipment combinations and coordinates independently.
Questions about this calculation
Does this resolution calculator choose equipment for me?
No. It evaluates only the displayed formula with the numbers you enter and does not make a purchase, compatibility or safety decision.
Why can the observed result differ?
Real optics and observing conditions add obstructions, transmission losses, aberrations, seeing, focus and measurement uncertainty that are outside the arithmetic model.
Can I use the result for navigation or safety-critical work?
No. SkyClock tools are transparent planning estimates, not certified navigation, engineering or safety instruments.
Need a dated lunar calendar? Browse official USNO moon phases for 2026–2050.