At the #AAS237 conference yesterday I went to a panel discussion on the effect of large constellations of satellites on astronomy from the ground. The thousands of satellites @spacex and others want to launch are a serious problem. 1/n

The launch of so many satellites might change the appearance of the night sky for ever and the trails they leave in astronomers' cameras and the potential for interference with radio telescopes are serious problems 2/n

Those problems are particularly acute for those searching for near-Earth or threatening asteroids, for example, though any large survey of the sky is affected. 3/n

It was good to see @spacex, Amazon's Kuiper project and @oneweb present, and to hear that the latter have dropped their plans from more than 40,000 satellites to 'only' 6372. All the speakers were positive about working together. 4/n

@OneWeb And a lot has been done. All three companies talked about making sure their satellites were fainter than 7th magnitude soon after launch, which would make them invisible to the naked eye and avoid the worst problems for large surveys 5/n