top of page

A Moon that Will Never see the Light of Day.....

So, the Chinese city of Chengdu is considering the idea of launching an artificial satellite that will look like the moon - though much brighter - and act as a light source for the city.

The Guardian has the story here:


I suspect this is the sort of 'announcement' that can show off how technologically competent a regime has become, without ever actually seeing the light of day. But even so, it got me thinking about how feasible the idea is, or could be.

A few issues spring to mind....

  • What orbit would it be in? To sit above a specific city all night every night, it would have to be in geostationary orbit.

  • That's tens of thousands of kilometres high, so it would have to be huge if it is to be comparable to the moon in the night sky. Something like 170 km in radius, by my no-doubt-simplistic calculations.

  • Also, to make full use of this enormous satellite in the sky on a nightly basis, they will have to move their city considerable closer to the equator. That could be a problem.

  • But maybe I'm missing something. Maybe it will be a little closer to the earth and therefore have to be so big. But if it's any lower, it will be moving across the sky and will only occasionally be above Chengdu. And when it does arrive, it might not be at night. Where will it be lighting up the rest of the time? Is that OK with everybody involved?

  • If it's to provide night-time light for Chengdu comparable to what it gets from street lighting now (when it happens to be overhead at the right time) it will have to be visible there for at least several hours at a time. But that can only be controlled by the height, so we're back to it being very far away again. Several kilometres high.

  • But that brings us back to size. To be visible and bright and comparable to the moon, it will have to be huge again. And most of the time, it will be nowhere near Chengdu.....

  • This is all to ignore the issue of light pollution and the effect on astronomy.

Maybe I'm missing something, or maybe it would easier for them to stick to reet lighting.....

Recent Posts

See All


bottom of page