Optical airmass and extinction estimate
Estimate why a low object is dimmer through a longer atmospheric path, using an extinction coefficient measured for your conditions.
Your inputs
Start with the example values, then replace them with your own. For tables, keep the vertical bar separators and use a dot for decimals.
This simplified educational calculation has stated assumptions. Do not use it for navigation, engineering safety or other safety-critical decisions.
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Result and workspace
Use the start button to open your result or activity.
How it works
Use the Kasten–Young optical airmass approximation with zenith angle 90° minus altitude. Extinction is coefficient × airmass; relative transmission is 10 raised to −0.4 times extinction. The coefficient is wavelength and weather dependent. The model excludes clouds, terrain and instrument losses and is restricted to altitudes of at least one degree.
Worked example
These sample results use the original example inputs in the form. They do not change when you edit your inputs; your own result appears in the workspace.
- Relative optical airmass: 1.9943
- Extinction from outside atmosphere: 0.3989 mag
- Additional extinction relative to zenith: 0.1989 mag
- Transmission relative to outside atmosphere: 69.2559 %
Read the result carefully
Results depend on the values and assumptions shown above. Change one input at a time to see its effect. A blank or unavailable result means the data does not support a calculation; it is not zero.