Milky Way visible from 13% of Malta

TL;DR

A University of Malta team measured the brightness of the night sky across the islands and reported, in the Journal of Environmental Management (2020), “87% of the area registering a NSB < 20.39 mag_SQM/arcsec² (Bortle Class 5 or higher) … with the Milky Way being visible for only 12.8% of the area”. News reports rounded this to “13%”. We checked that the summary matches the study and that the study’s numbers hold together.

1. The summary matches the study. The paper gives 12.8% (Bortle class 4 threshold) or 13.5% (the world atlas threshold); “about 13%” is fair. 87% is the share of land in Bortle classes 5–9, as stated.
2. The study’s numbers hold together and agree with the world atlas. Weighting the island results by land area gives 11.6% (the paper weights its 347 survey cells, giving 12.8%). The 2016 world atlas of night-sky brightness gave 11% for Malta.
3. The threshold matters. On the paper’s own sensitivity test, the visible share is 6.3% to 25.9% depending on the brightness threshold chosen. “About 13%” uses a standard, stated threshold.
4. The data are from 2017–2019. Measurements are from 2017–2019. On the island of Malta the class 4 area fell from 3.9% to 1.6% between the two surveys. We found no newer survey.
5. Verdict: supported (high confidence). The statement reports a peer-reviewed measurement accurately.

1. Supported
2. Largely supported
3. Not substantiated
4. Misleading
5. Contradicted

IN THIS REPORT

1 The claim and what we could verify

The claim record came from a MaltaToday headline, “Milky Way only visible from 13% of Malta”, which summarised the study. Following our rule to quote the speaker, not the headline, we read the study itself: Caruana, Vella, Spiteri, Nolle, Fenech and Aquilina (2020), “A photometric mapping of the night sky brightness of the Maltese islands”, Journal of Environmental Management 261:110196 [1], in its accepted version on arXiv [2]. The quoted wording is the paper’s abstract.

2 Method

Question. Does the statement report the study accurately, and are the study’s results consistent?

Evidence. We transcribed the study’s Table 1 (share of land area in each Bortle class, by island) into data/cc-053/caruana2020_table1.csv and recomputed the archipelago-wide shares by weighting each island by its land area from OpenStreetMap (tools/cc-053-report/calc.py; outputs in data/cc-053/checks.csv). We compared the result with the paper’s own comparison to the 2016 world atlas and with its threshold sensitivity test.

Grades. Caruana et al. (2020): B (observational measurement with a stated method and comparison). Verdicts follow the five-point scale in Appendix A.

3 What the data show

No part of the islands reached Bortle class 3 or darker. Class 4, where the Milky Way is clearly visible, covered 3.9% of Malta, 37.2% of Gozo and 83.3% of Comino in 2017/18, 12.8% of the islands overall. Weighting by land area gives 11.6%; the paper weights its one-kilometre survey cells, which include coastal cells, so the darker coasts count for slightly more. On the island of Malta, the second survey (2018/19) found class 4 had shrunk to 1.6%.

4 Where the evidence points different ways

5 Testing the claim

6 Verdict and requests for evidence

Why. Both figures are the study’s own, the study’s parts add up, and an independent atlas agrees. What this verdict does not say. It does not describe the sky in 2026: the survey has not been repeated nationally since 2019.

Evidence we are asking for

• From the University of Malta team or ERA: any repeat survey of night-sky brightness since 2019.
• From ERA and the Planning Authority: the status of national lighting guidelines.

7 Limitations

• We read the accepted manuscript on arXiv; the published version may differ slightly in wording.
• The world atlas figure (11%) is as reported by Caruana et al.; we did not recompute it.
• Sky Quality Meter readings vary with season, cloud and the Milky Way’s position; the study discusses these.

References

1. [1] Caruana J., Vella R., Spiteri D., Nolle M., Fenech S. & Aquilina N.J. (2020). A photometric mapping of the night sky brightness of the Maltese islands. Journal of Environmental Management 261:110196. doi:10.1016/j.jenvman.2020.110196. https://doi.org/10.1016/j.jenvman.2020.110196
2. [2] Same, accepted manuscript. arXiv:2002.04435. https://arxiv.org/abs/2002.04435
3. [3] Falchi F., Cinzano P., Duriscoe D., Kyba C.C.M. et al. (2016). The new world atlas of artificial night sky brightness. Science Advances 2(6):e1600377. doi:10.1126/sciadv.1600377. https://doi.org/10.1126/sciadv.1600377
4. [4] MaltaToday. Milky Way only visible from 13% of Malta (locator). https://www.maltatoday.com.mt/news/national/100416/milky_way_only_visible_from_13_of_malta
5. [5] MiŻien. Data and calculation: data/cc-053/; tools/cc-053-report/calc.py.

Appendix A: series standards and verdict scale

Every investigation in this series follows the same rules so that verdicts are comparable and challengeable.

Confidence

High: multiple independent lines of evidence agree. Moderate: evidence is relevant but incomplete or indirect. Low: evidence is thin, second-hand or conflicting.

Evidence grades

A experiment · B observational study with a control or gradient · C review, guidance or official statistics · D assertion or anecdote. ◆ marks a source known only second-hand.

Standards

• Quote the speaker, not the headline, with outlet and date, and link the original where possible.
• Separate the claim from the evidence offered for it, and say who made which statement.
• Grade the evidence and show differing views side by side where the evidence is unsettled.
• State what we could not access or verify, and what would change the verdict either way.
• Ask for the missing evidence in specific, answerable requests.
• Offer a right of reply where a check finds a claim Not substantiated, Misleading or Contradicted (or a pledge Not measurable, Off track or Missed), before wider circulation, and append responses.
• Correct errors openly with a version number and change log.
• Whistle-blow only on evidence: a verdict of Misleading or Contradicted requires documents or data that can be shown, not inference.
• Check every side. Government, opposition, NGOs and developers are held to the same standard.

Appendix B: revision log