Purpose of the Dwingeloo Radio Telescope
The Dwingeloo Radio Telescope was built for scientific research of radio waves from the Milky Way and the universe. As ASTRON no longer uses this telescope for that purpose, CAMRAS gives amateur astronomers and other interested parties the opportunity to experiment in the field of astronomy. This can be done by contributing to building receivers, making radio astronomical observations and developing computer programs to process and to interpret the observations.
Using the Dwingeloo Telescope for radio astronomy
– Radio waves from the universe
Radio astronomy uses different techniques and instruments than optical astronomy. Optical astronomy studies the universe in visible light. The wavelengths of visible light are approximately between 400 nanometer (violet) and 800 nanometer (red). The optical instrumentation consists of lenses (refractor) and mirror (reflector) telecopes to collect more light and to see more detail in the image. Amateur astronomers usually use an eyepiece (ocular lens) to view the image or a camera to capture and edit digital images. Professional astronomers use more advanced detectors that unravel all properties of light.
Radio astronomy studies the universe by means of radio waves between millimeter and decameter waves. For radio waves from the universe with wavelengths greater than about 30 meters, the outer layer of the atmosphere – the ionosphere – is not or hardly permeable anymore. The radio instruments consist of antennas, different types of constructions to collect more radio waves in a large wavelength range, and radio receivers and amplifiers.
Radio waves are a type of electromagnetic radiation, just like visible light, except that their wavelengths are much larger. In the universe, radio waves often arise in different places and different physical processes play a role. Some objects emit almost solely in visible light and can only be seen with an optical telescope. Other objects radiate almost exclusively in radio waves and can only be detected with a radio telescope. Still other objects emit both visible light and radio waves. Together with observations in visible light, radio astronomy gives a more complete representation of the universe that can also be supplemented with astronomical research using observation equipment suitable for sub-millimeter waves, infrared, X-ray and gamma radiation.
– Day and night observable
Just like a radio receiver at home can receive broadcasting stations 24 hours a day, radio astronomers can receive radio signals from the universe all day long: both at night and during the day while the sun is shining. Moreover, even during cloudy and rainy weather since radio waves go through clouds effortlessly.
– Dish antenna
A radio telescope such as the Dwingeloo Radio Telescope is a combination of an antenna at the focal point of a parabolic mirror construction of metal wire mesh; also called a dish antenna. Part of the receiver and amplifier is in the focal point directly behind the antenna, while another part is in the control house that rotates along with the telescope. The observation wavelength is set with the receiver and the dipole antenna must be suitable in size for the chosen wavelength.
The diameter of the mirror of the Dwingeloo Radio Telescope is 25 meter and the mesh size of the wire mesh is 8 millimeter. This construction makes this telescope suitable for astronomical observations at wavelengths between a few centimeters and a few meters.
– Directional sensitivity
A dish antenna with one dipole antenna in the focal point is sensitive in only one direction and can thus only detect one area in the sky at a time. The telescope cannot see any details within such an area. The size of that area – the beam – depends on the diameter of the mirror and the observation wavelength. For the Dwingeloo Radio Telescope, the beam at a wavelength of 21 centimeter is about half a degree; about the same size as the angle of the moon occupies in the sky. With a detection wavelength twice as large as 21 centimeter, the beam also becomes approximately twice as large, i.e. one degree.
In order to make a detailed map of the radio sky, the telescope must make many single-point observations with spacing of half a beam and combine them. And just like making star maps and atlases of nebulae and galaxies in optical astronomy, this is a lengthy and precise work.
– Data processing
Radio astronomers do not look at the universe like optical astronomers. In addition, radio waves are not sound waves. However, do radio astronomers never listen to the universe? Do they never listen to the noise or signals coming from the receiver? Actually, they do not listen. The amateur astronomers of CAMRAS work more or less in the same way as professional radio astronomers. The radio waves cause a very weak voltage on the antenna. After amplification, it is digitized, processed and stored on the CAMRAS servers for further processing. For example, the observations can be presented in real-time on a computer screen in the telescope. Or later after more data reduction the observations can be displayed in a graph or a map on a computer at home.
For demonstrations to visitors of the Dwingeloo Radio Telescope and also for monitoring during the observations, the radio waves captured and processed by the telescope can be made audible. Visitors can ‘listen’ to the universe as a supplement to the – more or less varying – images on the computer screen. Louder or weaker noise from the speaker corresponds to a more or less bright point on a radio map of the sky. When pointing the telescope at a special type of star, a so-called pulsar (a rotating neutron star), a ticking sound comes through the noise from the speaker. By measuring the time between the pulses and by carefully examining these pulses, radio astronomers can learn all about the pulsar, such as the cosmic distance and how quickly the pulsar ages.
Inventory of possibilities
Together with the Royal Netherlands Association for Meteorology and Astronomy, CAMRAS has made an inventory of a number of possible observing programs with the Dwingeloo Radio Telescope which are very suitable for amateur astronomers. And amateur astronomy can be much more than a personal hobby, for example:
- for certain types of research such as long-term monitoring, professional telescopes and astronomers are too expensive, but there may be opportunities and discoveries for amateur astronomers;
- redoing scientific research, so-called ‘retro-science’;
- making certain radio astronomical research suitable for educational and demonstration purposes.
The CAMRAS volunteers already have experience or experiment with a number of the activities below, while others are under development or in preparation.
- ‘Meteor scatter’ (recording reflections on plasma traces of meteors with suitable beacons; the sensitivity of the Dwingeloo mirror is many times greater, the field of view is obviously many times smaller than when using YAGI antennas).
- Sun (recording variations in radio clarity and the relation between optical and radio observations).
- Reflections of radio waves on NEOs (near-Earth objects), Moon, asteroids and planets (e.g. recording radio reflections on the surface of Venus and distance determination, also with reflection of signals from other stations).
- Jupiter and Io ‘Radio JOVE’ (on low frequencies, interaction with volcanic activity on Io and the interaction of the solar wind on the Jupiter magnetosphere).
- Comets (line radiation of molecules and continuum radiation).
- Pulsars and pulsar glitches (e.g. creating time series from a pulsar in a double system).
- 21 cm hydrogen line and other line radiation in the Milky Way and large galaxies.
- Continuum radiation and its polarization in the Milky Way and large radio sources.
- Time series of variable radio sources (e.g. variations of radio waves around black holes).
- Occultation of radio sources by the Moon (e.g. Tau A or pulsars).
- Passive SETI (e.g. monitoring of Kepler planets).
- Survey of radio transients: FRBs (fast radio bursts), RFRBs (repeating FRBs), RATs (radio transients), RRATs (rotating RATs).
Join as an amateur astronomer, for an educational assignment, or as a volunteer?
Those who are interested and would like to do one or more observations individually or with a small group of amateur astronomers, or for an educational project, can register as a user and make proposals via the Program Committee and apply for telescope time. See also our rates overview for telescope time (in Dutch).
If you want to contribute to developments, experiments and long-term observation programs, we advise you to sign up as a volunteer.
If interested you can contact the CAMRAS Program Committee and provide them with a concise description of what you are thinking about, and CAMRAS will contact you.