Build your own radio telescope
Submitted by minh on 22 May 2012
By Bogusław Malański and Szymon Malański
Radio telescopes observe the sky for radiation at wavelengths that are thousands to millions of times longer than visible light. The huge antennas that scientists have built to observe these wavelengths have become icons of modern technology. Arecibo Observatory, so big it was built into a bowl-shaped valley in Puerto Rico, is instantly recognisable from the James Bond movie GoldenEye, while Jodrell Bank has dominated the skyline of Manchester, UK, for half a century.
The resolution of a telescope’s images depends both on the wavelength at which it operates and on the diameter of its dish. The longer the wavelength, the worse the resolution; and the larger the diameter, the better the resolution. Radio waves have a much longer wavelength than visible light, which is one reason why professional radio telescopes are enormous. Their huge size also helps them to capture the faint radiation from dim and distant objects. Nonetheless, the basic technology behind radio telescopes is quite simple and with some cheap equipment and simple tools, it’s quite easy to build a simple but functional one of your own.
I called my radio telescope design RYSIA (a girl’s name), or RadiowyY Śliczny Instrument Astronomiczny – Polish for ‘beautiful radio astronomy device’. With RYSIA, you can carry out simple observations of objects that radiate brightly in the radio spectrum. This includes the Sun, our own planet, and man-made communications satellites such as Hot Bird, Astra and Sirius.
Local scrapyards, shops selling second-hand TV equipment and online auction sites such as eBay are good places to buy the parts you need.
Activities using your radio telescope
You now have a radio telescope that works on some of the same principles as the gigantic radio telescopes that are used to investigate the earliest days of the Universe, capturing radiation from very distant galaxies (see Mignone & Pierce-Price, 2010). Although your much smaller telescope cannot detect distant stars, you can use it to demonstrate to your students that the Sun and other objects radiate not only visible light but also radio waves. Furthermore, you can find the position of the Sun on a cloudy day, demonstrate that the surface of Earth emits radio waves, and locate satellites.
If you used a parabolic antenna to build your radio telescope, you will need to point its axis directly at the object you are observing. If you used an offset antenna, however, you must take into account the angle by which it is offset. Most manufacturers do not provide this parameter but it can easily be calculated (this can be an additional task for the students). In practice, the arm of the satellite dish on which the LNB is mounted indicates the direction from which the signal is received (figure 10).
Observing the Sun
Objects around us, including buildings, plants, people and even the ground under our feet, emit radio waves, reflected from the Sun or Earth. Try comparing readings for different objects. Thanks to the auditory signal from the satellite signal meter, you should be able to detect the location of buildings and trees around you easily, even when blindfolded. To make sure that the signal does not come from the Sun itself, make sure you carry out these experiments by pointing the dish away from the Sun.
Most astronomical phenomena produce electromagnetic radiation because they are hot. The higher their temperature, the shorter the wavelength they can produce. At around 5500 ºC, the Sun produces plenty of visible light as well as infrared and radio waves. Colder objects have to be detected using infrared or radio telescopes. You can demonstrate this by pointing your radio telescope at a hotplate as it heats up. It will only begin to emit visible light at around 700 ºC, but your telescope will detect the radio waves emitted well before that.
We have built this simple radio telescope using satellite TV technology, which allows it to detect spacecraft too. Professional radio telescopes do this too sometimes – Australia’s Parkes Telescope was used to communicate with Apollo 11 during its mission to the Moonw1.
The best-known communications satellites (e.g. Hot Bird, Astra and Sirius) are in geosynchronous orbits around Earth, which means they do not move in the sky, and orbit above the equator. This makes them easy to find. The Wolfram Alphaw2 database provides the location of many satellites.
Be aware that during the spring and autumn equinoxes, the Sun shines above the equator and can interfere with satellite reception when the Sun and the satellite are in the same area of sky. Wolfram Alpha has a map of the Sun’s location relative to a satellite, so this is easy to avoid.
If you have suggestions for improving the telescope or for further activities, please leave a comment at the end of the online articlew3.
Our radio telescope was inspired by a working model built by Peter Kalberla, an astronomer at the University of Bonn, Germany, and demonstrated at his 2011 course ‘Hands-On Universe: Connecting classrooms to the Milky Way’w4 in nearby Bad Münstereifel.
Mignone C, Pierce-Price D (2010) The ALMA Observatory: the sky is only one step away. Science in School 15: 44-49. www.scienceinschool.org/2010/issue15/alma
w1 – Learn more about how the Parkes Observatory supported the Apollo 11 mission.
w3 – Leave your suggestions for improvement and activities in the comments section at the end of this article.
w4 – Find out more about the course that inspired this article.
w5 – Learn more about Boguslaw’s planetarium (in Polish).
For an activity to investigate radio transmission and the propagation of electromagnetic waves in air, see:
To find out more about electromagnetic radiation and how it is used in astronomy, see:
The European Southern Observatory (ESO) is one of the partners in the radio observatory ALMA, the Atacama Large Millimeter/submillimeter Array, an ensemble of huge, high-precision antennas on the Chajnantor plateau in Chile’s Atacama region. Also on Chajnantor plateau is ESO’s radio telescope APEX.
Boguslaw Malański is a physics and astronomy teacher. He gained a physics degree and a PhD from the University of Łódź, Poland, after which he spent nine years as a physics lecturer at the University of the North-West in South Africa. He was also involved there in performing science experiments for local schools together with Pastor Bernd-Peter Jensen. Boguslaw is currently employed at the local planetarium and astronomical observatory in Łódź, where he teaches astronomy and physics. He also runs a small, non-profit experimentarium for local schoolsw5.
Szymon Malański, Boguslaw’s son, is a 5th-year student studying telecommunications and computer science at the Technical University of Łódź, Poland. He enjoys experimenting and is keen on classical analogue photography.
If you would like your students to discover that the Sun or a hotplate emits a lot more than just visible light, that visible light is blocked by the clouds but radio waves are not, or that the electromagnetic spectrum consists of a variety of very interesting radiation; if you want your students to be able to find the position of the Sun on a cloudy day or to locate geostationary satellites; if you would like them to distinguish polarised radiation from non-polarised radiation; if you want to use a radio telescope in your lessons, constructed by your students and capable of helping you to teach all these topics and much more, then you will definitely be interested in the ideas presented in this article.
Using cheap materials and easy-to-follow instructions, you can build a simple but functional small-scale radio telescope. The activities suggested in this article are both interesting and applicable to a range of scientific topics (e.g. orbits, light, radiation and its effects on the body, and the electromagnetic spectrum), which can be covered in physics, astronomy and biology lessons.
Vangelis Koltsakis, Greece