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Light pollution from SpaceX satellites may block view of stars, astronomers warn

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By Emma Beswick  & Joël Chatreau
Light pollution from SpaceX satellites may block view of stars, astronomers warn

After Elon Musk’s SpaceX successfully placed all 60 of its first Starlink v0.9 satellites into orbit last week, astronomers and astrophysicists alike have been expressing their concerns over the light pollution they could cause.

These were just the first 60 of a planned 12,000 satellites from SpaceX, which intends to use them to beam internet to the ground by the 2020s, reaching areas that are not yet connected.

Social media was initially awash with users posting images admiring the train of satellites.

But the launch soon sparked discussion, with astronomers calculating how several thousand satellites could change how we see the cosmos.

"Even in the spring, autumn and winter, around half a dozen #Starlink satellites will be visible at any time up to 3 hours before sunrise and 3 hours after sunset," astronomer Cees Bassa wrote on Twitter.

"Depending on how bright they end up being, this will have a drastic impact on the character of the night sky."

He also offered preliminary calculations on how many satellites would be visible from Earth, with his estimates showing of the first 1,584 satellites that are set to be launched — the trajectories of which have already been made public — around 15 will be visible for three to four hours after dusk and before dawn.

When questioned on the matter, multi-billionaire technology entrepreneur Musk argued there are already "4,900 satellites in orbit, which people notice ~0% of the time".

We need to move telescopes to orbit anyway," he added. "Atmospheric attenuation is terrible."

"I think the project itself is fantastic but, although it is almost like a film, I think that in the end will ruin the night sky a bit: now we think it's phenomenal, but we will eventually have to get used to seeing swarms of bright satellites," wrote Néstor Espinoza, astronomer from the Max-Planck-Institut für Astronomie in Germany.

Another concern expressed online was that the Starlink satellites would be particularly bright when reflecting sunlight because of their flat shape and the large solar panel.

It is not clear how bright the first batch of 1,600 v0.9 satellites will be when they reach their intended altitude of 550 km.

Musk said SpaceX was looking into ways to reduce how much light bounced off the satellites.

“Sent a note to Starlink team last week specifically regarding albedo reduction. We’ll get a better sense of the value of this when satellites have raised orbits and arrays are tracking to sun.”

In addition to changing how we see the sky, the satellites could also be a problem for professional astronomers, with the sheer number causing a visibility issue.

Given SpaceX is one of nine companies that are known to be working on a global high-speed internet network from space, the actual number of satellites that end up in orbit could be far higher than currently predicted.