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Radio waves are reflected by conducting surfaces, just as light is reflected from a shiny metallic surface, and according to the same laws of optics. A radio-reflecting telescope consists of a concave metal reflector (called a dish ), analogous to a telescope mirror. The radio waves collected by the dish are reflected to a focus, where they can then be directed to a receiver and analyzed. Because humans are such visual creatures, radio astronomers often construct a pictorial representation of the radio sources they observe. [link] shows such a radio image of a distant galaxy, where radio telescopes reveal vast jets and complicated regions of radio emissions that are completely invisible in photographs taken with light.
Radio astronomy is a young field compared with visible-light astronomy, but it has experienced tremendous growth in recent decades. The world’s largest radio reflectors that can be pointed to any direction in the sky have apertures of 100 meters. One of these has been built at the US National Radio Astronomy Observatory in West Virginia ( [link] ). [link] lists some of the major radio telescopes of the world.
| Major Radio Observatories of the World | |||
|---|---|---|---|
| Observatory | Location | Description | Website |
| Individual Radio Dishes | |||
| Arecibo Observatory | Arecibo, Puerto Rico | 305-m fixed dish | www.naic.edu |
| Green Bank Telescope (GBT) | Green Bank, WV | 110 × 100-m steerable dish | www.science.nrao.edu/facilities/gbt |
| Effelsberg 100-m Telescope | Bonn, Germany | 100-m steerable dish | www.mpifr-bonn.mpg.de/en/effelsberg |
| Lovell Telescope | Manchester, England | 76-m steerable dish | www.jb.man.ac.uk/aboutus/lovell |
| Canberra Deep Space Communication Complex (CDSCC) | Tidbinbilla, Australia | 70-m steerable dish | www.cdscc.nasa.gov |
| Goldstone Deep Space Communications Complex (GDSCC) | Barstow, CA | 70-m steerable dish | www.gdscc.nasa.gov |
| Parkes Observatory | Parkes, Australia | 64-m steerable dish | www.parkes.atnf.csiro.au |
| Arrays of Radio Dishes | |||
| Square Kilometre Array (SKA) | South Africa and Western Australia | Thousands of dishes, km 2 collecting area, partial array in 2020 | www.skatelescope.org |
| Atacama Large Millimeter/submillimeter Array (ALMA) | Atacama desert, Northern Chile | 66 7-m and 12-m dishes | www.almaobservatory.org |
| Very Large Array (VLA) | Socorro, New Mexico | 27-element array of 25-m dishes (36-km baseline) | www.science.nrao.edu/facilities/vla |
| Westerbork Synthesis Radio Telescope (WSRT) | Westerbork, the Netherlands | 12-element array of 25-m dishes (1.6-km baseline) | www.astron.nl/radio-observatory/public/public-0 |
| Very Long Baseline Array (VLBA) | Ten US sites, HI to the Virgin Islands | 10-element array of 25-m dishes (9000 km baseline) | www.science.nrao.edu/facilities/vlba |
| Australia Telescope Compact Array (ATCA) | Several sites in Australia | 8-element array (seven 22-m dishes plus Parkes 64 m) | www.narrabri.atnf.csiro.au |
| Multi-Element Radio Linked Interferometer Network (MERLIN) | Cambridge, England, and other British sites | Network of seven dishes (the largest is 32 m) | www.e-merlin.ac.uk |
| Millimeter-wave Telescopes | |||
| IRAM | Granada, Spain | 30-m steerable mm-wave dish | www.iram-institute.org |
| James Clerk Maxwell Telescope (JCMT) | Mauna Kea, HI | 15-m steerable mm-wave dish | www.eaobservatory.org/jcmt |
| Nobeyama Radio Observatory (NRO) | Minamimaki, Japan | 6-element array of 10-m wave dishes | www.nro.nao.ac.jp/en |
| Hat Creek Radio Observatory (HCRO) | Cassel, CA | 6-element array of 5-m wave dishes | www.sri.com/research-development/specialized-facilities/hat-creek-radio-observatory |
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