Historically, astronomy has played a key role in the development of science and technology while also having a large cultural impact. For example, explaining the orbits of the planets was important for understanding that the Sun, and not the Earth, was at the centre of the solar system; that had an enormous impact on our view of our place in the Universe. During the ‘space race’ and the cold war, when astronauts took the first photos of a spherical earth, it was the first direct evidence that the Earth was a sphere, just another planet. Such images emphasise the isolation of the Earth in space, and perhaps underline the fragility of the Earth’s ecosystems. Direct evidence of a greenhouse effect can be seen from Venus, which has been a ‘hot topic’ (excuse the pun!) in international policy in the last few decades. Also, understanding of our early Universe after the big bang has been found using telescopes such as WMAP and Planck. However, most astronomers also contribute their skills and knowledge to industry and culture in less well known ways. This blog post tells a less well known story, that modern wireless technology (which you are probably using to read this very blog post!) was developed by mathematicians, engineers and radio astronomers.
Electromagnetic waves that have wavelengths that are larger than 1mm in length are typically called radio waves. These wavelengths are used for communication between mobile phones, radio stations, Bluetooth devices, and of course radio stations. However, there are also non-terrestrial sources of radio waves. The first example was discovered by Karl Jansky in the 1930’s, when he was given the job of investigating sources of static that might interfere with radio voice transmissions. Jansky built an antenna built to detect 14.6 metre radio waves.
After isolating sources such as distant thunderstorms, he discovered a source that was independent of direction, with the intensity varying with the raising and setting of the Sun. However, the period was 23 hours and 56 minutes, which is the period of the Earth’s rotation and not the period of the Sun passing over the sky. This suggests that the Sun was not the source of background radio static, but that the source was outside of the solar system. After comparing his observations with optical astronomical maps, Jansky found that the source was coming from the centre of the Milky Way. This was the beginning of a new type of astronomy, which we call radio astronomy.
The first radio telescope used by Karl Jansky during the 1930’s, it was used to discover the Milky Way as an astronomical radio source. This lead to the start of radio astronomy. Credit: see http://www.nrao.edu/whatisra/hist_jansky.shtml
Since this discovery, large radio dishes have been built to create images of the radio sky. New sources of radio emission have been discovered since then. The most popular sources of radio emission in the universe include supernova remnants, pulsars, shock waves within galaxy clusters, and the supermassive black holes at the centre of large galaxies. However, due to large radio wavelengths, the resolution of radio images from a single dish are quite low. It was not for decades that many astronomical radio sources were understood or identified, due to the limitations in radio resolution.
The Robert C. Byrd Green Bank Telescope (GBT) in West Virginia, United States is the world’s largest fully steerable radio telescope. Credit: see https://en.wikipedia.org/wiki/Radio_astronomy – /media/File:GBT.png
Typically, a large radio dish will have a resolution of approximately 10 arcminutes (1 arcminute is 1/60 th of a degree) at a wavelength of 21 cm. The naïve way to increase the resolution of the radio telescope is to increase the size of the radio dish, which is like increasing the size of a lens in optical telescopes. But, the largest steerable dish has a size of 100m in diameter, and which is still limited to arcminute resolution; whereas an optical telescope, due to small electromagnetic wavelengths, can have arcsecond resolution (60 times smaller than an arcminute). This was a huge challenge and annoyance for radio astronomers: that it was not possible to see the radio sky in the same level of detail as optical astronomers. Scientifically this meant that cross-identification between radio and optical objects was difficult and so understanding and discovery of new objects was hindered.
This challenge of resolution was overcome by radio astronomers with the understanding of a mathematical calculation known as a Fourier transform. At the heart of the Fourier transform, is the understanding that it is possible to represent any signal as a superposition of pure sine waves of different phase and amplitude. This calculation is critical for understanding the (diffraction) limit of resolution of a telescope, and understanding methods of moving beyond them.
The method of moving beyond this limit has become what is known as radio interferometry, where it is possible to use a collection of radio dishes over large distances as a large radio dish. Each dish will measure a radio signal from the sky, the signals are correlated, interfered, and combined to increase the resolution of the final image.
Image of one of the first large radio interferometric telescopes, the Westerbork Synthesis Radio Telescope in the Netherlands. The radio signals collected by the antennae are combined to increase the resolution of the observed image. The techniques developed with this telescope played a role in inspiring modern WI-FI technology. Credit: See https://en.wikipedia.org/wiki/Westerbork_Synthesis_Radio_Telescope – /media/File:Westerbork_Synthese_Radio_Telescoop.JPG
The centre of the Milky Way in radio colour, created with a radio interferometer. Red indicates the lowest frequencies, green the middle frequencies and blue the highest frequencies. Each dot is a galaxy, with around 300,000 radio galaxies observed as part of the GLEAM survey. This survey was imaged using the Murchison Widefield Array located in Western Australia. Credit: Natasha Hurley-Walker (ICRAR/Curtin) and the GLEAM Team.
Radio astronomers that worked on these first interferometric telescopes developed an understanding of radio waves and Fourier transforms that provided a huge advantage for the development of the high-speed WI-FI standard. In the early 1990’s, WI-FI speed was limited by errors created from the signal bouncing and echoing off walls and objects of a room. This problem was made worse when a lot of information was sent across a single pure tone (single frequency) sine-like radio waves, limiting the possible data WI-FI data rate. However, it was found that by spreading the load of information across the radio band, reduced the echo as well as allowing for error correction in the transmission. This communication method was developed and patented by a world leader in radio astronomy, the CSIRO in Australia. It was not until the mid 2000’s that this standard had become main-stream in WI-FI technology.
The take home message from this post, is that doing pure blue skies research, such as radio astronomy, can give people the skills and insight to solve problems effectively in industry. This continues today because astronomers need to be cross-disciplinary in mathematics and engineering in order to understand the science resulting from their telescopes and instruments. Places like MSSL provide such an opportunity, where instruments are built with scientists and engineers, especially with the recent GAIA and Euclid missions.
By Luke Pratley, Ph.D student at MSSL.
- For more information on how CSIRO developed and patented the WI-FI standard, watch https://youtu.be/esA9YhdgvIg
- For more information on what radio astronomers see in the radio sky, see this talk by Dr. Natasha Hurely-Walker https://www.ted.com/talks/natasha_hurley_walker_how_radio_telescopes_show_us_unseen_galaxies .