The “shooting stars” of the Tau Herculid meteor shower may be visible later this month, but you may want to hear them.
The excitement among meteorite enthusiasts increases as we get closer the expected meteorite explosion which could be produced by a concentrated trace of dusty debris from the core of comet Schwassmann-Wachmann 3 (SW 3) Monday night early Tuesday morning (May 30-31).
Even if you can’t get a good view of the show due to clouds or light pollution, you can “watch” the meteor shower a different way: listening to it on the radio!
Related: 2022 Meteor Rain Guide: Dates and Display Tips
Under certain conditions, meteors can reflect radio waves in the same way that the ionosphere propagates transmissions between widely separated amateur radio operators. The ionosphere usually reflects frequencies below 30 megahertz (MHz), but is transparent at higher frequencies, such as the FM band (88 to 108 MHz).
These high-frequency (short-wavelength) radio signals generally pass through the atmosphere unobstructed in a straight line; they cannot follow the curvature of the Earth to reach a listener beyond the horizon. However, when certain layers of the upper atmosphere ionize, they may reflect signals back to earth far away. The lowest layer of this type, 60 to 70 miles (96 to 112 kilometers) up, is called the E layer of the ionosphere, and this is the altitude where most meteors are seen.
Thus, as a meteoroid vaporizes as it passes Earth’s atmosphere, briefly ionizes air molecules along their path. Forming an expanding column or cylinder several miles or more in length, these ions can disperse and reflect radio waves, just as a high-altitude ray reflects sunlight and leaves a bright trail against the sky. darkened after sunset. But because ion tracks disperse quickly, reflected radio waves usually last only a few seconds.
Tiny particles tend to vaporize at the bottom of the E layer. Large particles, on the other hand, begin to flame higher. And predictions of the spilled particles of comet SW 3 suggest that most of these will be large. These meteors produce a more lasting ionization and, as they begin to “ignite” higher, they can reflect signals from more distant transmitters.
On the ground, the presence of the meteor is signaled by the momentary improvement of the FM reception from a distant station.
How to listen to meteorites on the radio
For this radio method to work, find a frequency where no nearby FM station is broadcast. You will have more chances of success by scanning the low frequency end of the FM band, below 91.1 MHz. Why there? Because this is where the lower power plants are located, mostly run by universities, and they are usually free from local interference from high power commercial stations. In fact, unless you live in a very unpopulated region of the country, your chances of finding an open frequency without interference above 91.1 MHz are quite small, so you’ll need to tune in to a distant station with a clear frequency below 91.1 MHz. .
FM Atlas, published between 1970 and 2010, provided listings of all FM stations in North America, with the unique feature of frequency-by-frequency maps. Bruce Elving, editor of the FM Atlas, was a longtime advocate and expert on all things FM. He died in 2011, but as a tribute to his love and dedication to FM radio, on the 21st final edition of FM Atlas (2010) is available free of charge, courtesy of AmericanRadioHistory.com. You can also see at complete list of AM and FM stations in the 2010-2011 edition of the M Street Directory.
How do meteors sound?
Normally, when you are tuned to an “empty” radio frequency, you only hear a noise. But as meteors pass through the atmosphere, a distant or silent station will “suddenly” enter for a fraction of a second to several seconds. You may also hear what initially sounds like a “pop” or a whistle, and as the ionization trail dissipates, the station fades quickly. Due to its altitude, meteors better reflect signals from stations 800 to 1,300 miles (1,300 to 2,100 km) from you.
When should you listen to meteors?
The best time to listen is when the radiant is 45 degrees above the horizon seen from a point halfway between you and the emitter. At the rush hour forecast for a possible meteorite explosion on Tuesday morning, parts of Maine and the Canadian provinces of New Brunswick, Nova Scotia and Prince Edward Island will have radiant near this preferred altitude, while eastern New York, New England, and southern Quebec will have radiation close to that preferred altitude. not to be left behind, at about 50 or 55 degrees.
In addition, it is best to tune a station located in a direction perpendicular to the radiant. Because the radiant SW 3 will be close to the bright orange star Arcturus in the Boötes constellationwhich will be towards the western part of the sky, the best listening directions will be north and south of you.
Most meteors are heard but not seen
If you are watching meteors while monitoring your radio, most of the time, you will hear a reception “ping”, but you will not see any meteor showers corresponding to the sky. Remember that most of the meteors you hear are about halfway between you and the radio station, about 400 to 650 miles (650 to 1,050 km) away. Therefore, they occur near the horizon or just below. In the 1970s, members of the Nippon Meteor Society in Japan who conducted extensive records of radio meteors noted that only 20% to 40% of meteors heard on the radio were observed visually simultaneously.
What if you can’t find a clear frequency?
Particularly in large metropolitan areas, finding a clear or empty FM frequency can be almost impossible, even below 91.1 MHz. In many ways, finding a clear frequency seems to go hand in hand with trying to find a dark sky free of light pollution. You will probably have a much better chance in rural or rural areas.
But if you can’t find a clear FM frequency, don’t despair. You can still hear meteorites livemeteors.com. A Yagi antenna in the Washington, DC metropolitan area constantly detects 55- or 61 MHz analog television signals in Ontario reflected by meteorite tracks. When a meteor passes, ping! – there is an echo. It’s the best thing about having free access to a giant government radar!
Good luck, and good listening!
Joe Rao is a guest instructor and professor in New York Hayden Planetarium (opens in a new tab). He writes about astronomy for Journal of Natural History (opens in a new tab), the Farmers’ almanac (opens in a new tab) and other posts. follow us on Twitter @Spacedotcom (opens in a new tab) and on Facebook (opens in a new tab).