The Sounds Of The InterStellar Space
As Voyager 1 recedes from the solar system, researchers are listening for interstellar music (plasma waves) to learn more about conditions outside the heliosphere.
Scifi movies are sometimes criticized when explosions in the void make noise. As the old saying goes, in space, no one can hear you scream. Without air there is no sound.
But if that's true, the sounds of interstellar space were heard by astronomers?
It turns out that space can make music - if you know how to listen.
Some plasma wave data was played for astronomers and The sounds were solid evidence that Voyager 1 had left the heliosphere.
The heliosphere is a vast bubble of magnetism that surrounds the sun and planets. It is, essentially, the sun's magnetic field inflated to enormous proportions by the solar wind. Inside the heliosphere is home. Outside lies interstellar space, the realm of the stars
For decades, researchers have been on the edge of their seats, waiting for the Voyager probes to leave. Ironically, it took almost a year to realize the breakthrough had occurred. The reason is due to the slow cadence of transmissions from the distant spacecraft. Data stored on old-fashioned tape recorders are played back at three to six month intervals. Then it takes more time to process the readings.
The thrill of discovery when some months-old data from the Plasma Wave Instrument reached his desk in the summer of 2013. The distant tones were conclusive: Voyager 1 had made the crossing.
Strictly speaking, the plasma wave instrument does not detect sound. Instead it senses waves of electrons in the ionized gas or plasma that Voyager travels through. No human ear could hear these plasma waves. Nevertheless, because they occur at audio frequencies, between a few hundred and a few thousand hertz, we can play the data through a loudspeaker and listen. The pitch and frequency tell us about the density of gas surrounding the spacecraft.
When Voyager 1 was inside the heliosphere, the tones were low, around 300 Hz, typical of plasma waves coursing through the rarified solar wind. Outside, the frequency jumped to a higher pitch, between 2 and 3 kHz, corresponding to denser gas in the interstellar medium.
So far, Voyager 1 has recorded two outbursts of interstellar plasma music--one in Oct-Nov. 2012 and a second in April-May 2013. Both were excited by bursts of solar activity.
We need solar events to trigger plasma oscillations.
The key players are CMEs, hot clouds of gas that blast into space when solar magnetic fields erupt. A typical CME takes 2 or 3 days to reach Earth, and a full year or more to reach Voyager. When a CME passes through the plasma, it excites oscillations akin to fingers strumming the strings on a guitar. Voyager's Plasma Wave Instrument listens - and learns.
We're in a totally unexplored region of space and expect some surprises out there.
In particular, plasma waves are not excited by solar storms. Shock fronts from outside the solar system could be rippling through the interstellar medium. If so, they would excite new plasma waves that Voyager 1 will encounter as it plunges ever deeper into the realm of the stars.
The next sounds from out there could be surprising indeed.
Sunset Solar Eclipse
On October 23rd, 2014, the Moon will pass in front of the sun, off-center, producing a partial solar eclipse visible in most of the United States
Sunsets are always pretty. One sunset this month could be out of this world. On Thursday, Oct. 23rd, the setting sun across eastern parts of the USA will be red, beautiful and - crescent-shaped.
It's a partial solar eclipse. In other words, the New Moon is going to 'take a bite' out of the sun.
A total eclipse is when the Moon passes directly in front of the sun, completely hiding the solar disk and allowing the sun's ghostly corona to spring into view. A partial eclipse is when the Moon passes in front of the sun, off-center, with a fraction of the bright disk remaining uncovered.
The partial eclipse of Oct. 23rd will be visible from all of the United States except Hawaii and New England. Coverage ranges from 12% in Florida to nearly 70% in Alaska. Weather permitting, almost everyone in North America will be able to see the crescent.
The eclipse will be especially beautiful in eastern parts of the USA, where the Moon and sun line up at the end of the day, transforming the usual sunset into something weird and wonderful.
Observers in the Central Time zone have the best view because the eclipse is in its maximum phase at sunset. They will see a fiery crescent sinking below the horizon, dimmed to human visibility by low-hanging clouds and mist.
Warning: Don't stare. Even at maximum eclipse, a sliver of sun peeking out from behind the Moon can still cause pain and eye damage. Direct viewing should only be attempted with the aid of a safe solar filter.
During the eclipse, don't forget to look at the ground. Beneath a leafy tree, you might be surprised to find hundreds of crescent-shaped sunbeams dappling the grass. Overlapping leaves create a myriad of natural little pinhole cameras, each one casting an image of the crescent-sun onto the ground beneath the canopy. When the eclipsed sun approaches the horizon, look for the same images cast on walls or fences behind the trees.
Here's another trick: Criss-cross your fingers waffle-style and let the sun shine through the matrix of holes. You can cast crescent suns on sidewalks, driveways, friends, cats and dogs-you name it. Unlike a total eclipse, which lasts no more than a few minutes while the sun and Moon are perfectly aligned, the partial eclipse will goes on for more than an hour, plenty of time for this kind of shadow play.
A partial eclipse may not be total, but it is totally fun.
