Last week SpaceX launched 60 Starlink telecommunication satellites. the first major launch of its ambitious plan to launch a fleet of up to 12,000 satellites.  The goal? to eventually create ultra-fast internet services around the world.

Sightings around the world of the satellites trailing across the night sky were posted online. One Dutch UFO website was inundated with more than 150 reports from people wondering if it may be UFOs.

Astronomers have concerns.

However, Not everyone is excited about the plan, including, notably, astronomers.  The initial excitement quickly gave way to dismay as they began to calculate the potentially drastic impact on people’s views of the cosmos.

Cees Bassa, an astronomer at the Netherlands Institute for Radio Astronomy said:

“I saw that train and it was certainly very spectacular. With that comes the realisation that if several thousands of these are launched it will change what the night sky looks like.”

.The Starlink satellites, which were at an altitude of 280 miles (450km) on Tuesday, were still visible with the naked eye and taking about five minutes to cross from one horizon to the other, meaning they appear at predictable times in a given location.

It is not clear what their eventual brightness will be when they reach their operating orbit of 340 miles in the coming month.

Darren Baskill, an astronomer at the University of Sussex said:

“Everyone’s quite surprised by how bright they are. I live on the outskirts of Brighton in light-polluted skies and I could easily see this line of satellites going across the sky.”

Elon Musk on Twitter.

Elon Musk addressed some of the concerns on Twitter, initially suggesting that the satellites would be in darkness when the stars were visible. Others have disputed this, including Bassa who has done some preliminary calculations of the number of Starlink satellites likely to be visible to observers. Since the satellites are higher than the Earth’s surface, they remain illuminated by sunlight after sunset here.

“My aim was to show people these satellites were going to be more visible than people said they would – amongst them Elon Musk,” Bassa said.

His estimates suggest that once the first 1,584 satellites are launched, for which the trajectories have already been made public, there will be about 15 satellites clearly visible above the horizon for three to four hours after sunset and before sunrise.

This means that in winter there would be several hours of the night during which no satellites would be visible. But in summer the satellites would be visible all night.

Once all the 12,000 satellites are launched (assuming they are placed in similar orbits) 70 to 100 would be visible at night during the summer months, Bassa calculates.

“These mega constellations are going to add drastically to the number of satellites that are visible at any time,” he said.

Néstor Espinoza, an astrophysicist at the Max Planck Institute for Astronomy, in Heidelberg, said:

“It’s basically a private company staining our sky for everyone. It’s interesting that there’s no consensus about it. No one asked us.”

SpaceX is just one of nine companies known to be working on global space internet, meaning the eventual number of satellites could be far in excess of this.

The satellites, in addition to changing the face of the night sky, could be problematic for professional astronomers, said Espinoza.

“We deal with satellites all the time. Whenever they come into your image you have to find ways to fix that. If you put 12,000 in the sky that will be a problem.”

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