Radio astronomy
| Radio astronomy | |
|---|---|
| What it is | Studying natural radio emissions from space |
| License needed | None for receiving |
| Early pioneers | Karl Jansky (1932); Grote Reber, W9GFZ (1937 backyard dish) |
| Jupiter and the Sun | NASA Radio JOVE, around 20 MHz |
| Amateur projects | |
| Hydrogen line | 1420.405 MHz (21 cm) |
| Meteors | Echoes from distant VHF transmitters |
| Typical receiver | Software-defined radio |
| Amateur society | Society of Amateur Radio Astronomers (SARA) |
| Organizations | |
| Professional | National Radio Astronomy Observatory (NRAO); Green Bank Observatory |
Radio astronomy is the study of objects in space through the radio waves they give off naturally. Professional observatories use dishes many meters across, but a great deal can be heard with amateur equipment: bursts from the Sun and Jupiter on HF, the faint hiss of hydrogen gas in the Milky Way at 1420 MHz, and the echoes of meteors burning up in the upper atmosphere. Because radio astronomy only listens, no license is needed, and many hams find it a natural next step from shortwave listening and SDR experiments.
Origins
The field began with radio engineers rather than astronomers. In 1932 Karl Jansky detected natural radio emission coming from outer space.[1] A few years later, in 1937, Grote Reber, a radio amateur who held the call sign W9GFZ, built a parabolic dish 31.4 feet across in his back yard in Wheaton, Illinois, with his own money, to follow up Jansky's discovery.[1] His dish is now on display at Green Bank, West Virginia, and the NRAO Amateur Radio Club holds his old call sign.[1]
The National Radio Astronomy Observatory (NRAO) was founded in 1956.[2] Its former site at Green Bank, now the Green Bank Observatory, is home to the Green Bank Telescope and lies inside the National Radio Quiet Zone, where transmitters are tightly controlled to protect sensitive receivers.[3] The observatory also has a 40-foot telescope used for education.[3]
Jupiter and the Sun
Radio JOVE is a NASA education project, running since 1999, that teaches students and amateurs to observe the radio emissions of Jupiter, the Sun and the Milky Way.[4] Its original kit is a simple receiver tuned to 20.1 MHz.[4] The newer RJ 2.1 kit uses an SDRplay receiver and records a wide band of frequencies at once.[4] With Radio-Sky Spectrograph software, observers can display the signal as a spectrogram, and the project keeps an archive of observations.[4]
Jupiter gives off intermittent storms of radio noise that a modest receiver and antenna can pick up. The Sun produces solar radio bursts when flares and eruptions send streams of charged particles outward. Type III bursts sweep quickly from high to low frequency; slower Type II bursts accompany shock waves that can lead to space weather effects on Earth.
Hydrogen line
Hydrogen, the most abundant element in the universe, emits a faint signal at 1420.405 MHz, a wavelength of 21 centimeters, when it is in its neutral atomic form.[5] Mapping this hydrogen line across the sky reveals the spiral arms of the Milky Way, and the Doppler shift of the signal shows how fast each cloud is moving.[5] Amateurs now detect it routinely with a dish about a meter across, a low-noise amplifier made for 1420 MHz, an inexpensive SDR and a small computer such as a Raspberry Pi.[5] Averaging the received spectrum over several minutes makes the hydrogen line rise out of the receiver noise as a small hump.
Meteors
Meteors entering the atmosphere leave trails of ionized gas about 100 km up that briefly reflect VHF signals.[6] By tuning to a distant, steady transmitter that is normally out of range, a listener hears a short "ping" each time a meteor trail reflects it. In Europe, a favorite target is the French GRAVES space surveillance radar on 143.050 MHz; an SDR, a small Yagi and a waterfall display can show hundreds of echoes an hour during a strong shower.[6] Counting echoes over months shows the rise and fall of the annual meteor showers.
Getting involved
The Society of Amateur Radio Astronomers (SARA) is a nonprofit group for amateur radio astronomers. It publishes the SARA Journal, supports projects such as Radio JOVE and the SuperSID very low frequency receiver, which detects solar flares through their effect on the ionosphere, and holds an eastern conference at Green Bank Observatory.[7] Groups such as the British Astronomical Association also publish practical guides to meteor detection and radio observing.[6] Many hams also take part in related citizen science through HamSCI.
See also
References
- ↑ 1.0 1.1 1.2 Grote Reber, Radio Astronomy Pioneer, Dies, NRAO.
- ↑ The Science of Radio Astronomy, NRAO.
- ↑ 3.0 3.1 What is the Green Bank Observatory?, Green Bank Observatory.
- ↑ 4.0 4.1 4.2 4.3 NASA's Radio JOVE Project, NASA.
- ↑ 5.0 5.1 5.2 Designing a Home Radio Telescope for 21 cm Emission, arXiv, October 2024.
- ↑ 6.0 6.1 6.2 Meteor Radar SDR Receiver (FUNcube Dongle), David Morgan, British Astronomical Association.
- ↑ Society of Amateur Radio Astronomers, SARA.