The first of a major series of satellites produced by Elon Musk’s SpaceX corporation have been launched, and are already causing consternation among astronomers (see update below). A string of 60 satellites have been seen crossing the night sky, and the plan is eventually to launch 12,000 such satellites.
The launch took place on 24 May and in the past few nights observers have witnessed and photographed a long strand of objects crossing the sky, easily visible with the naked eye. Estimates of their brightness suggest that the objects are around magnitude 3.5. Writer Will Gater reports via Twitter: ‘From suburban skies it appeared like a faint, grey line with random sparkling points along it. The brightest, at the rear, was comparable to the star Mu Serpentis, which is ~mag +3.5.’ He added that the train of objects spanned some 9 degrees of sky.
Although the objects will eventually move into a spread of orbits, including some higher ones, so they will become less obvious, the prospect of such an invasion of the night sky has filled observers with alarm. Reassurances that the satellites will be visible only during twilight apply only to lower latitudes, as over much of the USA. From Britain and much of northern Europe, the satellites will be visible all night during the summer months.
This project will certainly increase significantly the number of satellites that will be visible and which will affect astrophotographers in particular than at present. One observer suggests that when the constellation is complete there will be more satellites visible than stars with the naked eye.
The Starlink constellation of satellites, which has been approved by the US Federal Communications Commission, is designed to provide satellite-based broadband services.
Predictions of the appearance of the initial launch can be obtained from https://www.n2yo.com/ which indicates that there will be several evening passes over the UK in the next few nights.
Note added 28 May You can now get predictions from www.heavens-above.com, which has the advantage of providing predictions for both the leader and trailer of the swarm, which can differ by half an hour, and gives a star map showing the exact path across your sky for your location. For more help on using heavens-above.com, see our page on predicting the ISS and other satellites.
Robin Scagell, 27 May: I observed a pass of the string of satellites at 00:09 BST from St Lawrence Bay, Essex. The majority of the objects were about magnitude 4 or fainter, but one or two appeared about mag 2.0 or 2.5. The brightness of individual objects changed during the pass. The string of satellites now occupy probably 40º or more of sky, as two or three were considerably separated from the rest.
Robin Scagell, 28 May: The pass at 22.46 went close to Arcturus. No satellites were visible with the naked eye, but with binoculars several were spotted in a line. The brightest were now about magnitude 6.
Robin Scagell, 30 May: Although the satellites are now around mag 6 or 7, they are still in a line and are an unusual sight with binoculars, though taking 40 minutes for the entire pass, so now spread out about halfway around the Earth. I observed the pass between 22:55 and 23:35 BST as the satellites went through the Plough. The first satellites were close to Mizar, but with time the track shifted to the east. They in some way resembled a shoal of little fish in a line, with groups of them in twos or threes chasing each other but long gaps in between. Although some reports suggest that they can flare to magnitude –1, all those I followed remained at around 6th magnitude.
Robin Scagell, 1 June: The video below shows the passage of a few satellites through the Plough on 1 June, in approximately real time. Notice that some of the satellites do flare briefly, though none became brighter than about 6th magnitude.
Update 3 June 2019
The International Astronomical Union has issued a statement detailing the problems which large satellite constellations such as Starlink pose for the advance of astronomy. The IAU is calling for urgent discussion on ways ‘to mitigate or eliminate the detrimental impacts on scientific exploration as soon as practical’.