Atmospheric Seeing & Cloud Cover
Space weather can be perfect, but if there's cloud, haze, or smoke between you and the aurora, you won't see it. Lumina computes a unified seeing score (0–100) that combines three independent atmospheric factors into a single go/no-go metric.
What is the seeing score?
The seeing score answers one question: "How much of the aurora light will actually reach my eyes?" It runs from 0 (blocked — don't bother) to 100 (excellent — ideal conditions) and is shown as the primary coloured line on the atmospheric seeing chart.
| Score | Label | What it means |
|---|---|---|
| 85–100 | Excellent | Pristine conditions — clear sky, good visibility, clean air. |
| 60–84 | Good | Some cloud or light haze but aurora should be visible. |
| 35–59 | Fair | Marginal — cloud, haze, or aerosols are degrading the view. You might catch glimpses. |
| 10–34 | Poor | Heavy cloud, thick haze, or bushfire smoke. Probably not worth it. |
| 0–9 | Blocked | Can't see the sky — fog, overcast, or extreme smoke. |
The three factors
1. Cloud block (altitude-weighted)
Not all cloud is equal. Lumina fetches low, mid, and high cloud cover from Open-Meteo and weights them by how much they actually block the aurora sightline:
- Low cloud (stratus, ~500 m) — sits directly in the aurora viewing cone at 5–15° above the southern horizon. Weighted at 70%.
- Mid cloud (altostratus, ~3 km) — partially obstructs the viewing cone. Weighted at 20%.
- High cloud (cirrus, ~7 km) — mostly above the viewing ray and often translucent. Weighted at 10%.
Cloud cover is sampled at two points — your location (centre) and a southern sample point (the direction aurora appears). The two are blended 40% centre / 60% south to produce the cloud block fraction.
Hovering a point on the seeing chart shows the per-layer breakdown (e.g. "L 74% / M 55% / H 84%") so you can see why the score is what it is — thick low cloud hurts much more than high cirrus.
2. Visibility (boundary layer)
Meteorological visibility — fog, mist, rain, and surface haze — is fetched from Open-Meteo as horizontal visibility in metres. Lumina applies it as a residual attenuation : it only bites into the fraction of sky that cloud hasn't already blocked. This avoids double-counting (stratus is low visibility — we don't penalise the same phenomenon twice).
3. Aerosol optical depth (AOD)
Dust storms and bushfire smoke can block aurora even under a perfectly clear sky. Lumina fetches aerosol optical depth (AOD) from the CAMS Global atmospheric composition model via Open-Meteo's Air Quality API. AOD measures total column extinction at 550 nm and is converted to transmission via the Beer-Lambert law: \( T = e^{-\mathrm{AOD}} \).
This catches an Aussie aurora hunter trap: clear skies, good visibility, but invisible aurora because of bushfire smoke at altitude. The gap between the solid seeing-score line and the dashed cloud-block line on the chart is the visibility + aerosol penalty — if the lines overlap, clouds are the only issue. If the seeing line drops below the cloud line, haze or smoke is making things worse.
Reading the atmospheric seeing chart
The seeing chart shows two lines through the night:
- Solid coloured line — the full seeing score (cloud + visibility + AOD).
- Dashed grey line — cloud block alone. The gap between the two lines shows the additional impact of visibility and aerosols.
The chart has a natural y-axis: 100 (excellent, green) at the top, 0 (blocked, red) at the bottom. Hovering any point shows a breakdown: cloud cover with per-layer percentages, visibility status, and AOD transmission.
Where the data comes from
- Cloud cover — Open-Meteo weather API (ECMWF IFS + ICON global models). Hourly, includes low/mid/high layer breakdown.
- Visibility — Open-Meteo weather API. Horizontal visibility in metres, hourly.
- Aerosol optical depth — Open-Meteo Air Quality API (CAMS Global Atmospheric Composition Forecasts). 3-hourly, 45 km resolution, global coverage.
Directional sampling
Lumina fetches cloud and air quality data at five offset points around your location (centre, north, south, east, west) at user-configurable distances (default 75 km). This lets Lumina:
- Tell whether a short drive in any direction would get you under clearer skies.
- Compute the cloud block for the specific horizon direction — aurora appears south, so the southern sample point carries the most weight.
- Show per-direction charts so you can see at a glance which way is clearest.
Clearing detection
Lumina scans the forecast timeline looking for a significant drop in cloud cover. If the sky goes from > 70% to < 30% in the forecast, it flags a clearing and tells you when to expect it. This is one of the most practically useful features — knowing that the clouds should break at 11 PM means you don't give up at 10 PM.
Worth travelling?
If your primary location is clouded out but one of your other saved locations has clear skies — and the aurora probability justifies the drive — Lumina will flag it with a travel recommendation. In field mode this becomes a move alert with an estimated drive time from your current GPS position.
Limitations to be aware of
- Cloud forecasts aren't perfect. Open-Meteo is good but not infallible, especially for patchy or convective cloud that can form and clear faster than the model predicts.
- AOD is 3-hourly. CAMS Global updates every 12 hours with 3-hourly output — aerosol data is coarser than the hourly cloud and visibility data.
- AOD includes stratospheric aerosols (>10 km) that minimally affect horizon-angle aurora viewing. During major volcanic eruptions, the seeing score may be slightly over-penalised.
- Fog and low cloud can form in valleys and coastal areas even when the forecast says clear — local topography matters.
- Cloud layer heights are pressure-level based (Open-Meteo / ECMWF convention). For sites above ~500 m elevation, effective low-cloud altitude shifts upward.
The best strategy: use Lumina's seeing score as a guide, but always check something like the BOM satellite viewer before committing to a long drive.