In the January episode of The Sky at Night, Tim Stevenson highlighted how light pollution is a growing problem for radio astronomers
While radio astronomers are used to handling some radio interference from terrestrial sources, and a few air or space borne transmitters, the new megaconstellations of internet access satellites – which number in the thousands – are a much greater problem.
In the January episode of The Sky at Night I talked a bit about this new threat, but as it’s hard to explain the problem of these new satellite systems in a short TV interview, I will go into more detail here. It’s a complicated issue and it will help readers if I can give them a bit more background on the subject, so they can begin to understand the impact on the relatively young science of radio astronomy –a field which, after all, will have the greatest chance of discovering advanced extraterrestrial civilisations.
Radio astronomy is protected by international law, through the ITU (International Telecommunications Union) and its Radio Regulations. These Radio Regulations define certain ‘silent’ frequency bands, where transmitters are not allowed to operate. Although this was adequate for the early years of this new branch of astronomy, the Universe ‘speaks’ in a very broad range of frequencies and therefore modern radio astronomy needs to often ‘listen’ in bands assigned to transmitting users. This is possible by building telescopes in very remote and protected areas of the planet where the use of the radio spectrum is minimal. In these ‘Radio Quiet Zones’, all radio transmitters are banned. Indeed, mobile phones, laptops and even smart watches are not allowed. The difficulty is that, even in Radio Quiet Zones, we can’t escape air- and space-borne transmitters and have to cope with them.
The power of radio astronomy
Radio observations of the Universe can inform us about a vast variety of processes, in galaxy, star and planet evolution. So choosing one example to illustrate the impact of the new radio interference sources does not do justice to the scale of science that Square Kilometre Array (SKA) radio telescopes can do, but here goes.
The Universe is mostly empty, but gas is relatively common, and gas molecules emit radio signals which are unique to them. Readers of this magazine will be familiar with the concept of redshift, where light emitted by something moving quickly has its frequency shifted, and displacement applies to radio signals as well as optical light. This means that the further away – hence the further back in time – we look for a particular molecule, the lower its frequency will be. So what was a single frequency of interest has become a range of frequencies. For molecules that are particularly important for star evolution, we want to be able to visualise their distribution over time/ distance and effectively create a map of the evolution of the Universe over time. The example I gave on the show was carbon monoxide (CO). For such molecules, in distant galaxies where the SKA has the power to look, the frequency is found in a region where the satellite megaconstellations are now transmitting strongly and we are becoming blind to certain times in the past (and therefore stages of stellar evolution), which is extremely worrying. That’s why we are raising awareness on the issue.
Tim Stevenson has over 40 years experience as an engineer in space and ground-based astronomy and space science
Looking back: The Sky at Night
31 March 1985
On The Sky at Night episode that aired back on 31 March 1985, Patrick Moore took a look at a raft of discoveries being made using data from the Infra-Red Astronomical Satellite (IRAS) – the first infrared space telescope. A joint project between the US, Netherlands and the UK, the satellite launched on 25 January 1983 and operated for 10 months, observing 250,000 targets. The first observatory to fly above Earth’s infrared-absorbing atmosphere, IRAS opened a new window on the Universe. It made the first ever detection of solid material around the discs of stars – namely Vega and Fomalhaut.
Thought to be sand-sized dust at the time, it was an early indication of the circumstellar discs that modern day observatories are imaging today. (To find out how exoplanets grow, see page 68).
The telescope also made several serendipitous discoveries, as it uncovered six of the 22 comets found that year, picking up the infrared radiation from their ‘warm’ tails against the background of space.
Despite only operating for 10 months, IRAS achieved much. Its legacy was continued by the many infrared observatories that followed, such as Spitzer and the Wide-field Infrared Survey Explorer (WISE), all leading up to the James Webb Space Telescope.
The Sky at Night team are taking a break this month and will return in April for more astronomy and spaceflight news and observing advice. In the meantime, young astronomers can catch up on Out of This World, a wonderful 10-episode guide to spaceflight hosted by Dr Maggie Aderin-Pocock and her daughter Lori. The series features special guests and covers spacecraft design, living in space, the search for extra-terrestrial life and the robotic rovers exploring the bodies of our Solar System.
Watch the entire series via bbc.co.uk/iplayer
