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  Night Sky
 

Enjoy the starry night skies
Be a considerate neighbor. Reduce nighttime glare.
Shield your outside lights downward.
Let the stars light up the night.

September 2015 night sky

—Charlie Christmann

Radio Tom

There is no better known amateur radio astronomer around than New Mexico’s own Tom Ashcraft. He is well-known for his radio solar observations; but he is also recognized for his observations of Sprites above thunderstorms, the radio sounds of the sun, radio returns from meteors streaking through our atmosphere, U.S. space radar signals, and now, Jupiter.

Ashcraft’s observations were somewhat unintentional; his target was the sun. He regularly listens to the noise generated by our star and records all sorts of phenomena from solar flares to solar tsunamis. By coincidence on August 18, 2015, Jupiter was very near the sun and was in view of his solar antenna. What he recorded that day from Jupiter is known as a Jupiter radio storm, a somewhat random event.

Sounds of Jupiter

Jupiter’s radio storms, like the one Ashcraft observed last month, is created in processes similar to those that create the lasers we are familiar with that power our DVD players. The difference is the size of the laser. DVD lasers are less than an inch in size creating visible light. Jupiter’s lasers are thousands of miles long and create radio waves. Depending upon the process, Jupiter’s radio waves range from shortwave signals (similar to AM radio stations) to microwaves.

While lasers are well-known today for emitting light, lesser known are masers and radio lasers. Laser is an acronym for “Light Amplification by Stimulated Emission of Radiation.” In the early days of laser technology, scientists first created masers—the ‘M’ stands for microwave as in microwave oven. Light, microwaves, and radio waves, and indeed x-rays, are all forms of the same thing, electromagnetic radiation. The difference between them is their frequency. Radio waves wiggle a few thousand or million times per second, microwaves wiggle in the billions of times per second. Visible light wiggles in the range of hundreds of trillions of times per second; X-rays wiggle even faster. To make a laser, maser, or radio laser, there must be a defined area that adds energy to the wave. The size of the area needed is small for lasers, but very, very large for radio lasers. We are talking regions thousands of miles in size for radio lasers.

Jupiter is large enough to be a great radio laser. Having two-and-a-half times the mass of all the other planets in our solar system, Jupiter is amazing in many ways. Consisting primarily of hydrogen and helium, with a likely solid center, Jupiter also creates a huge magnetosphere as its gas rotates around the planet in bands.

Earth’s magnetic field is feeble, measuring around 0.00003 Teslas (30 uT) at the equator. A common refrigerator magnet measures 0.005 Teslas (5 mT). Jupiter’s field measures in at 0.000428 Teslas (428 uT). Jupiter’s radio emissions are a result of its magnetic field, even outshining the sun in radio frequencies.

One source of radio noise, discovered in 1955, comes from its polar regions. Ionized gasses flow toward the Polar Regions, accelerated in the magnetic fields and create microwave radiation in a process known as the “cyclotron maser mechanism.” Similar processes occur in Earth’s largest particle accelerators.

What Tom Ashcraft received from Jupiter was generated at shortwave radio frequencies. Those radio signals, originating more than 593 million miles away, were created by Jupiter’s Moon Io interacting with Jupiter’s magnetic field. Io is known to be volcanically active, hurling ionized gasses, much of it sulfur, into space. Io orbits well-inside the influence of Jupiter’s magnetosphere. That ionized gas collects in a donut-shaped region around Jupiter called the “Io torus.” As Io orbits through this torus of tenuous gas, it creates a wake, like a boat on a lake, behind it creating “Alfven waves.” These waves fuel a stream of energetic gas into the Jovian poles measured in trillions of watts of power. By contrast, high powered FM radio stations broadcast one hundred thousand watts. The gas follows the magnetic field lines into the polar region creating a radio laser in the shape of a hollow cone of energy radiating away from the planet. As Jupiter rotates, so do the cones. If Earth is inside the narrow edge of the cone, we hear the radio signal, otherwise we hear nothing. To catch the sounds of the storm, both Io must be in the right place to pump its energy into Jupiter and Earth must be in the right place to be inside the cone edge.

Ashcraft was lucky, Earth enters the cone at unexpected times, surprising listeners with unscheduled radio storms. To hear Ashcraft’s recording of Jupiter, go to the Spaceweather.com archives for August 21, 2015, or enter this shortened web address into your browser: goo.gl/MQ3Rlh.

Ashcraft, or someone like him, may be the first to observe changes to Jupiter’s magnetic field. Every eleven years, the sun flips its magnetic field, exchanging its north and south poles. Every three hundred thousand years on average, the Earth also flips its poles. So should Jupiter. Science has never seen Jupiter flip its magnetic field and has no way to predict when it might happen. All we can do is listen to Jupiter’s radio storm signals and wait.


Night Under The Stars

The Rio Rancho Astronomical Society will hold its fifth annual Night Under the Stars fundraiser on September 19, from 4:00 to 11:00 p.m., at Rainbow Park Observatory, 301 Southern Boulevard, in Rio Rancho. There will be a silent auction, Papa Murphy’s Pizza, and a special guest speaker —Dr. Robert Fugate, creator of the Starfire Optical Range. For further details, visit www.rrastro.org.


 
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