Moonless dark-sky sampling
Inspect half-hour samples across a UTC day when the Sun is below astronomical twilight and the Moon is below the horizon.
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
A sample qualifies when the Sun altitude is below −18 degrees and the Moon altitude is below 0 degrees. The displayed times are samples, not exact interval boundaries. Cloud, terrain, artificial light and Moon scattering near the horizon are not modelled.
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.
- Qualifying samples: 17
| UTC instant | Altitude | Azimuth | Sun altitude |
|---|---|---|---|
| 2026-10-08T00:00:00.000Z | -16.4128 | 66.8078 | -44.3108 |
| 2026-10-08T00:30:00.000Z | -11.354 | 72.1372 | -39.8242 |
| 2026-10-08T01:00:00.000Z | -6.1312 | 77.2197 | -34.9115 |
| 2026-10-08T01:30:00.000Z | -0.7915 | 82.1434 | -29.6938 |
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.