ESO claims satellite mega-constellations will ‘severely affect’ some telescopes

5 Mar 2020

The Visible and Infrared Survey Telescope for Astronomy at Paranal Observatory, Chile. Image: Y Beletsky (LCO)/ESO

An ESO study has found that satellite mega-constellations in orbit will, in some cases, severely limit a telescope’s ability to see into deep space.

Earlier this year, SpaceX became the operator of the world’s largest active satellite constellation with a project named Starlink. The company hopes to launch 42,000 satellites into orbit over the coming decade in order to create a global satellite internet network accessible from some of the most remote places on Earth.

However, astronomers have already complained that even though the constellation currently includes only a few hundred satellites, it is already hampering the ability to study the universe through telescopes. Now, the European Southern Observatory (ESO) has conducted a study to see just how affected telescopes are by these new satellites.

The study – published to Astronomy and Astrophysics – looked at 18 satellite constellations currently under development by SpaceX, Amazon, OneWeb and others, amounting to more than 26,000 satellites in total. It found that ESO’s Very Large Telescope and upcoming Extremely Large Telescope will be “moderately affected” by the constellations.

Telescopes are worst affected during long exposures when up to 3pc of observations could be ruined during twilight, the time between dawn and sunrise and between sunset and dusk. Shorter exposures would be less impacted, with fewer than 0.5pc of observations affected.

Fisheye-lens image of space seen from a telescope showing which satellites would be visible with the naked eye.

This annotated image shows the night sky at ESO’s Paranal Observatory around twilight, about 90 minutes before sunrise. The blue lines mark degrees of elevation above the horizon. Up to 100 satellites could be bright enough to be visible with the naked eye during twilight hours. Image: ESO/Y Beletsky/L Calçada

What stargazers can expect

However, the greatest impact could be felt by wide-field surveys, especially those done using telescopes. The ESO study found that the US National Science Foundation’s Vera C Rubin Observatory, for example, would have between 30pc and 50pc of exposures “severely affected”, depending on when in the year it is and what time of night.

Attempts to mitigate this – such as changing schedule times – would not work in the case of the Rubin Observatory, researchers added. However, making the satellites darker in colour could help.

Looking at the potential impact on the night sky for professional and amateur astronomers, ESO researchers found that up to 100 satellites could be bright enough to be visible with the naked eye during twilight hours.

While this number will plummet as the night gets darker and the satellites fall into the shadow of the Earth, the number of satellites that can be seen by stargazers will be reduced by 90pc above 30 degrees of elevation over the horizon.

Updated 3.04pm, 5 March 2020: This article was amended to clarify that painting satellites a darker colour could, in fact, help overcome telescope observations. Also, the number of satellites seen 30 degrees of elevation over the horizon would be fewer than previously suggested. 

Colm Gorey was a senior journalist with Silicon Republic