A practical observing guide
Measure the sky. Help build the map.
A Sky Quality Meter measures the brightness of the sky background. A careful reading records a real place and time. Together, repeated observations help document the UAE’s night sky and test our calculations.
A simple, repeatable routine
- Choose a safe, open observing spot. Keep away from direct lamps, car headlights and reflective surfaces. Use a location you are comfortable making public if you submit it. Do not measure through a window.
- Check the meter. Identify the model. Make sure the sensor or lens is clean and dry, and use it as supplied. Allow its temperature to settle after moving from an air-conditioned space. Follow the instructions for your model.
- Wait for a dark sky. In the UAE, astronomical darkness starts roughly 75–90 minutes after sunset, depending on the date and location. One hour can be too early. For the actual time, open the night planner, choose your site and date, include the early evening in your session and read “Astronomical darkness”. The precise criterion is the Sun at least 18° below the horizon. Choose a Moon-below-horizon interval for the standard moonless comparison. Your eyes need dark adaptation for visual checks; the meter does not need your eyes to adapt.
- Point straight up. The zenith is directly overhead. Hold the sensor clear of your face and clothing. Keep the direction the same for the whole set. If you measure another direction, mark it as such and describe it.
- Discard the first reading, then record five. Keep the individual values and times. Report their median—the middle number after sorting—and the highest value minus the lowest. If clouds or a light change the scene, record that change rather than silently deleting inconvenient results.
- Record the circumstances. Note location, UAE time, instrument, cloud, haze and anything near the meter’s field: the Moon, the Milky Way, a building or a lamp. Submit the measured result without adjusting it to match Skydust.
Manufacturer guidance: Unihedron SQM and SQM-L FAQ. Five readings and the reporting format are Skydust’s collection protocol.
An example you can follow
After the first reading is discarded, you record 21.36, 21.40, 21.38, 21.39, 21.37.
Sorted: 21.36, 21.37, 21.38, 21.39, 21.40.
Submit 21.38, repeat count 5, spread 0.04. Use the approximate midpoint time of the set, in GST (UTC+4).
A narrow spread shows the readings were consistent during that short set. It does not remove calibration error or prove the sky was free of cloud.
Tell us which meter you used
| Instrument | What matters |
|---|---|
| SQM-L family | The lensed meter has a response about 20° wide at half maximum. Sensitivity extends beyond that width; it is not a hard-edged cone. |
| Original SQM | Its much broader response is about 84° wide at half maximum. Obstructions and bright features affect it differently. |
| Other instrument | Describe its response, filters, calibration and pointing. Smartphone or naked-eye estimates are not interchangeable with an SQM reading. |
SQM values use a broad instrument response. They are not exactly Johnson V-band measurements simply because both use mag/arcsec². A calibration based on SQM data is therefore an empirical comparison, with instrument and sky-colour differences to consider.
The serial number is optional and helps identify instrument offsets. It remains private review information.
What about moonlight, haze and cloud?
Moonless, cloud-free readings help constrain the natural and artificial background. Moonlit readings help test the scattered-light estimate, but the Moon must be well away from the meter’s sensitive field. Direct lunar light can dominate a reading.
Haze is part of the phenomenon we want to understand. Do not relabel a hazy night as clear air: record the haze separately from cloud. Readings through cloud or during twilight may be useful context, but they are excluded from the standard clear-sky calibration.
The current fit accepts only reviewed zenith readings from the SQM-L family, with repeated measurements, cloud information and compatible model data. It excludes high AOD and difficult Moon geometries. These are practical selection rules, not proof of scientific accuracy.
Keep readings from cloudy, broad-field or unusual conditions accurately labelled. Approval for sharing and eligibility for a particular fit are separate decisions.
Where your reading appears
After review, consented observations can appear on the public SQM map and in its data download. Map coordinates are rounded to three decimal places (about 100 metres); observation times and instrument details remain visible. Separate research exports may retain the submitted coordinate precision. No contributor names, notes, serial numbers or IP addresses appear on the public map.
The standard map comparison requires moonless astronomical darkness and consistent zenith readings. Observations without stored Sun and Moon context appear under all reviewed readings. Return on separate nights to build a meaningful history.
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