Jason Kendall
William Paterson University
Amateur Astronomers Association of New York

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Voyager Out in Interstellar Space

The Voyager Spacecraft has left the Solar System! Wow! That's the big news. It's a first for humanity. Perhaps someday people will follow in spaceships and pass the little probe and wave hello, but for now, Voyager 1 is sending back data from the furthest reaches ever attained.

But, it begs some questions. And that's what science is all about: questions. First, what's a Voyager? What's the solar system? Is there a doorway or something that Voyager went out? Is there a wall it jumped? It's really far away and no one is on board, so how do we know? Where is it going next?

Well, let's begin with a great story. Back in 1972, the scientists out at Jet Propulsion Laboratory in Pasadena, California realized that all the gas giant planets would be lined up in a way that would make a trip to all four possible, but only if they launched in 1977. So, using the best technolagy of the time, they built a pair of spaceships, more like unmanned probes, both the size of a small car and sent them on their way. Each probe had a television camera, a radio dish, and various instruments and gizmos to measure what we can call "space weather". In 1979, both of them fly by Jupiter, taking pictures that astonished the world. They were the first close-ups of the biggest planet. In 1980 and 1981, they went by Saturn. Scientists changed Voyager 1's path, so that it went close to Titan, but that made it go up and away from the other planets, leaving Voyager 2 to fly by Uranus in 1986 and Neptune in 1989. Until the Hubble Space Telescope was launched these were the only pictures ever of these distant worlds. And today, they provide the only images of Triton, the large moon of Neptune.

The probes are powered by a nuclear battery, which is slowly running low. So, they turned off the camera after the final image in February of 1990. That last picture turned around and looked home. Earth was a tiny, blue dot barely visible in the glare of the Sun. From there, all the Voyagers could do was measure what we call the "space weather". The Sun has a wind that continuously streams away. Sometimes, the Sun belches out a huge storms of charged particles. Billions of tons of superhot gas streams away from the Sun, carrying along a magnetic field. If it hits the Earth, then we see the aurorae. But these streams are so large, that they go past and around the Earth, and sometimes Earth isn't even where they are going. The Voyagers are billions of miles away, and it can take many weeks for the streams to make it out to where they are.

As the Voyagers travelled for the past 40 years, they were swept over by these waves of particles many times, just like waves washing up on a shore. The Voyagers have really long antennae, just like the old rabbit-ear television antennae that they used to have back in the 1970's and 1980's. Ask your mom or dad what those liked like when they were kids! So, as these waves swept by, the antennae "heard" them. You can hear the same kind of thing. Get a radio with a long antenna, you might already have one. Turn it to an AM radio station with just static or quiet music. Now take your new blackberry or cell phone, anything that you can use to communicate, and turn it on. Now move your cellphone around near the radio antenna. You'll hear buzzing on the radio! The cellphone emits radio waves, and the radio detects them, just like Voyager. But your cell phone is not putting out the energy of the Sun. The Sun pumps out so much energy that if you could capture all the noon-day sunlight falling on a football field, you could melt a block of steel. Luckily, we're pretty small.

Anyway, so the Voyagers have seen these waves, and the scientist have watched them for decades(!) and know what it's like. At some point, these waves of the solar wind meet the gas particles between the stars, slow down, bunch up and stop. That changes what the Voyagers see with their antennae. Scientist have been looking at the gas between the stars, called the interstellar medium (which is actually quite large, and made up of small gas particles), and they know how the waves should sound in that gas with Voyagers' ears.

That's what they've found. A big storm from the Sun months ago finally reached Voyager 1, and washed over it. That made the particles around it move in a way that Voyager could hear. The waves have a different wavelength between the stars compared to near the Sun. Think about it like this. Imagine that there is a really nice family, and the youngest daughter was born blind and deaf. That's a very hard thing, but her family loves her, and her older brother takes good care of her, and takes her places so she experiences the world. So, imagine that her brother tells her that they are going to the beach, and that she's never been to the beach. So, she asks, "What's the beach like?" and he says "Take off your shoes and feel the wind in your toes when you sit down." She does, and the wind feels good, brushing her toes gently. "Now," he says, let's see how it feels at the beach. Just use your toes to feel." He drives her to the beach, and she laughs and sticks her toes out the car window, feeling the wind. They get to the beach and she walks across the sand, sensing something wonderful is going to happen. Then he takes her hand to the water's edge, and says "Now feel with your toes." The waves touch her toes, and she laughs, knowing that she's reached the beach. She's now in a new place.

The little girl is the Voyager. She's made it to the water's edge. Her toes are dipping into the big ocean, which goes on what feels like forever. The waves are different. They are waves of water, and not puffing wind. The transition that the Voyagers have seen is like this. The types of waves are different, and it's "thicker" out where they are, just like the water is "thicker", or rather denser, than water. The gas between the stars was predicted to have the kinds of waves and the density that has just been observed.

So, the girl's world is like the Solar System. She's always near home, and her big brother takes care of her. Just like the planets are always near the Sun, and the Sun provides the light and warmth for life on Earth.

Unlike the girl at the beach, the Voyagers will never come home. They will do what the little girl couldn't and sail out onto that uncharted sea. The voyagers are travelling a million miles a year, or perhaps 38000 miles and hour, or about 17 miles every second. In the time it took you to read this, Voyager has gone an additional 1700 miles. It doesn't have rockets, it is just coasting. The gas that's out there is not thick enough to stop it, so off it goes. It's going out there, and in 40,000 years, it'll pass about 3 trillion miles from a star. By then, the battery will be drained, and it'll be a message in a bottle, a record of humanity out among the stars. And that's not sad, because it's carrying a gold record. The record has 115 pictures, music, greetings and sounds from Earth. We have truly sent ourselves out into space. Perhaps one day, a million years from now, our distant descendants will fly out to meet Voyager. Perhaps they'll bring it home. Perhaps they'll just fly along beside it and protect it, allowing it to continue its exploration forever.



About Jason Kendall

I am currently adjunct faculty at William Paterson University teaching astronomy. I hold a Master of Science in Astronomy from New Mexico State University. I am also a board member of the Amateur Astronomers Association of New York. Since 2008, I have led the Inwood Astronomy Project which brought over 200 events of stargazing and public astronomy outreach to upper Manhattan, including the historic Inwood Star Fest, where Inwood Hill Park lights were turned off as part of the 100 Hours of Astronomy event in IYA2009. This was the first time in New York City history when park lights were turned off for an astronomy event. I've also focused on park safety due to an uptick in sexual assaults in Washington Heights and Inwood during 2011. I've worked to make our parks safer by encouraging public use of parks at night through night-time events with Park Rangers. I have led numerous "starwatching parties" and astronomy events in New York City, New Mexico, Minnesota, New Jersey, Connecticut and Texas. I am also proud to have been part of the NASA/JPL Solar System Ambassador Program from 2009 to 2012. It all started way back in the fourth grade by the encouragement of two noted astronomers, Charles Schweighauser and Bart Bok. I saw Saturn through Charlie's telescope at then Sangamon State University on a clear Illinois night, and Bart encouraged me under those stars to study hard to come visit him at Kitt Peak National Observatory. I finally did make it down there about a decade after Bart passed away, and I found the favorite spots in Tucson, Arizona, where Bart and his wife Priscilla would spend when they were not gazing at the stars. Bart and his wife were pioneers in the study of the Milky Way, and their studies of the starforming regions called Bok Globules. It's even in my family. My great-grandfather was a Midwestern minister who used to preach his sermons out under the dark, cloudless nights. He always believed that getting out and experiencing the wonders of the natural world was a central part of being human. My family has always been inspired by his words: "We look up to look within." I hope that you'll join me under the stars or at one of my talks.

Come see what's up in the sky!

Jason Kendall

We look up to look within

William Paterson University Department of Physics American Astronomical Society Astronomical Society of the Pacific Amateur Astronomers Association of New York

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