Comparison of Light‑pollution readings on The Nightmap

Data sources and method

Two versions of light pollution maps were compared, based on David Lorenz's Light Pollution Map.

To compare the data sets, locations were searched in the The Nightmap’s search bar and the marker/area around the pin to obtain the Dark Sky Rating. For Milky Way or telescope destinations, the Milky Way and Astro Tourism layers were toggled on and the location was selected from the search suggestions. The table below summarises the measured brightness values (higher mag/arcsec² indicates darker skies).

Major Australian cities

The table below summarises measurements taken at the central business districts of major Australian cities. Each location was identified using The Nightmap’s search function. The measured Dark Sky Rating values from 2022 and 2024 are compared, along with notes on observed changes.

Milky Way hotspots and telescope locations

The table below summarises measurements taken at selected Milky Way viewing spots and telescope/astro‑tourism locations across Australia. Each location was identified using The Nightmap’s search function with the Milky Way or Astro Tourism overlay enabled. The measured Dark Sky Rating values from 2022 and 2024 are compared, along with notes on observed changes.

Overall, these results show that most rural Milky Way and astro‑tourism destinations in Australia have experienced only small (0–0.1 mag) reductions in darkness between 2022 and 2024. The largest drop recorded was 0.11 mag at Fingal Head, but even there the skies remain moderately dark (Bortle 5). Several premier sites—The Jump‑Up Sanctuary, Lake Tyrrell and The Pinnacles—retain their exceptional darkness with virtually no change. These findings reinforce that while urban brightening is evident around major cities, protected rural sites continue to offer excellent stargazing opportunities.

Dark‑grey Bortle 1 zones (shrinking)

The darkest zones (mag/arcsec² > 21.7, Bortle 1) are shown as dark‑grey on the map. A comparison between datasets illustrates that these areas have shrunk.

Implications

• More driving required for dark skies: The contraction of the dark‑grey region means stargazers in south‑eastern Australia need to travel farther from towns and small cities to escape light domes. Areas that were Bortle 2 in 2022 are now Bortle 3 in 2024, especially around Brisbane and Melbourne.
• Urban brightening: All major Australian cities measured show lower mag/arcsec² values in 2024 compared with 2022. Although differences (0.12–0.27 mag) might seem small, sky brightness is logarithmic; a 0.25 mag drop corresponds to roughly 25–30 % more sky brightness.
• Protected sites remain dark: Destinations such as Killen Falls or Jasper maintain high dark‑sky quality with little change in brightness, showing the importance of dark‑sky preserves and careful lighting management.

Conclusion

The comparison of The Nightmap datasets highlights subtle but measurable increases in light pollution between the 2022 and 2024 layers. Major Australian cities have become ~0.2 mag/arcsec² brighter, which shortens the radius of Bortle 2/3 zones around them. Dark‑sky enthusiasts should consult the updated 2024 map when planning trips, as Bortle 1 dark‑grey areas have shrunk—notably in south‑eastern Australia. Milky‑Way hotspots such as Killen Falls retain excellent conditions (~21.6 mag/arcsec²), while telescope/education facilities like Green Point Observatory show only a slight decline in darkness. Overall, the 2024 data underscore the need for ongoing dark‑sky conservation and careful management of urban lighting to preserve Australia’s world‑class night skies.