New Satellite Threat to Visual Observing

[Hugh]

Hi Everyone

The text as below is from an SPA Newsletter and may be of interest to imagers in particular.  Otherwise something to look out for.

Newsletter text

The first of a major series of satellites produced by Elon Musk's SpaceX corporation have been launched, and are causing consternation among astronomers. 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 some of the objects are as bright as magnitude 2.  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. Robin Scagell in Essex and Paul Sutherland in Kent found that the brightest objects of the train were as bright as the stars of the Plough, that is around magnitude 2.

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.

Impact on astronomy

Currently there are around 4900 satellites in orbit, so when Starlink is fully deployed this number will significantly increase. There have been many contentious and ill-informed statements on Twitter about the impact. Some fans of SpaceX have said that astronomical observing should shift to space anyway, and have pointed out that there are more aircraft in the sky than satellites. At any one time there are about 10,000 planes in the sky, according to FlightAware, so this is indeed true. However, Starlink will overwhelm this number.

Currently, most astronomical observation at visible wavelengths is carried out from the ground, and this is likely to continue for many years to come as new instruments such as ESO's ELT are built. Space instruments are many orders of magnitude more costly than those on the ground, and are at much greater risk of failure. So shifting operations into space is not a viable option. Satellite trails are readily identifiable, but as the number increases so will the likelihood of observations being spoiled.

Observing reports

Robin Scagell: I observed a pass of the string of satellites at 00:09 BST on 27 May 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 occupied probably 40º or more of sky, as two or three were considerably separated from the rest. While the bright objects were easily visible with the naked eye, the whole string was best seen using binoculars.

On a second pass at 01:46 the objects were significantly more spread out, with some lagging considerably behind the front runners. As time goes on, this spread will presumably become greater.

Clear skies (where possible)

Hugh

[ApophisAstros]

At any one time there are about 10,000 planes in the sky, according to FlightAware, so this is indeed true. However, Starlink will overwhelm this number.

Surely not over each observer / imager.

Oh well have to do a few more subs a bit shorter to process all these streaks out.
Roger