World famous astronomer Sir Patrick Moore has condemned Blackpool Tower's laser beam – which can be seen across Lancashire – for wrecking the sky at night.
A green light has been installed at the top of the Tower and it started shining in 10-minute bursts on Friday.
The beam can be seen 30 miles away across the county, and will continue until the end of the Blackpool Illuminations on November 4.
The veteran presenter of BBC series The Sky at Night and former chairman of the British Astronomical Association, said the light – which has been affecting astronomers – should be stopped.
He said: "Light pollution is a huge problem. I am not saying we should turn all the lights out, that is not practical, but there are some things which are very unnecessary.
"The Blackpool Tower light is certainly something I do not think we should be doing. I very much oppose it."
Sir Patrick said councils across Britain must play a central role in reducing light pollution. He said: "There are lots of practical things that can be done.
"For example, councils should make sure they fit street lights facing downwards to minimise the effects."
The astronomy department has had to choose observation sites around the world where skies are darker and clearer. Scientists visit Chile, South Africa, Hawaii and La Palma, and say the Preston area is not suitable for detailed research because the sky is too light.
Dr Barbara Hassall, deputy course leader for astronomy, said: "We used to have a student observatory in Moor Park but it has become too light. We have just moved to Alston Observatory out of the city as a good compromise to avoid all the lights and glare in Preston."
Dr Stewart Eyres, from the Centre for Astrophysics at Preston's University of Central Lancashire, said the laser has added to a spiralling problem.
He said: "Every day you can see fewer and fewer stars in the night sky. We have already relocated our research to places like South America. The sky is too light around here.
"We don't notice the skies getting slowly lighter, but because the light on the Tower is so big, it stands out. If we made more effort to reduce light pollution generally, the light on Blackpool Tower would just be a spectacle for people to enjoy, but at the moment it is adding to a mounting problem."
A spokesman for Blackpool Tower said: "All necessary approvals have been granted to operate the lighting effects."