A simple star count inside the Great Square tells you how much light pollution is washing out your night sky, and this week’s observing window offers a clear test, The Guardian reported.
The four corner stars — Alpheratz, Scheat, Markab and Algenib — are bright enough to spot from suburban locations, but the stars inside the square disappear one by one as artificial light brightens the sky.
The experiment, laid out in The Guardian’s Starwatch column, asks observers to look south from London at 2000 GMT on 9 November, find a spot away from direct lighting, and let their eyes adjust for at least 20 minutes without checking a phone. Then they count every naked-eye star inside the square, excluding the four corners.
The number of stars visible maps directly to sky quality. Seeing just one star means a relatively poor sky, four stars an average one, seven a good one, 13 a very good one, and about 35 an exceptionally dark sky, according to the thresholds The Guardian published.
Grandgoldman.com, which covered the same Starwatch experiment, describes the same scale and notes that one star signals significant light pollution, four typical suburban conditions, seven a rural or dark-sky location, 13 an excellent dark-sky site, and 35 a pristine night sky.
Beyond the view itself, grandgoldman.com reports that light pollution obscures stars while also affecting wildlife, human health and energy consumption. The outlet frames the count as a form of citizen science that raises awareness of dark skies and can inspire people to seek darker locations or push for better lighting practices in their communities.
Grandgoldman.com advises using averted vision — looking slightly to the side of the square to catch fainter stars — and avoiding nights with a bright moon, which washes out dim stars. It also recommends repeating the count on different nights to see how conditions vary and recording results to compare with friends or local astronomy groups.
When should I look for the Great Square? The Guardian’s chart shows the view looking south from London at 2000 GMT on 9 November, with the square high in the sky. Grandgoldman.com describes it as a prominent autumn asterism around 8 PM local time, with corners roughly aligned to the cardinal directions.
Why do I have to wait 20 minutes before counting? Both outlets stress that eyes need at least 20 minutes to adapt to darkness, and that checking a phone’s bright screen will ruin that dark adaptation.
Should I count the four corner stars? No — both sources exclude Alpheratz, Scheat, Markab and Algenib, counting only the stars inside the square.
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