A snowman made by my daughter’s boyfriend reflects the light of the 10-day moon last night. Taking time exposure photos on a tripod by moonlight can make night scenes appear as bright as day. The three bright objects across the top of the frame are (from left): Mars, Procyon and Sirius. Details: 16mm lens at f/2.8, 25-second exposure at ISO 800. Photo: Bob King
Can you tell the days are getting longer? I didn’t think so. But there’s no question the nights are getting brighter. As the moon waxes toward full and reaches the apex of its arc through the zodiac this week, lots of sparkly evenings are in the offing. Between first-quarter and full moon phases during the winter months, the moon’s monthly path takes it near the top of the sky. Tonight you’ll find it in Aries the Ram and Monday in Taurus the Bull. Moon shadows will be as short as those cast by the sun in summer. No surprise there: this coming week’s full moon will be in the same place in the sky as the sun was last June.
The constellations of summer brought us their share of delights but now they’re "on vacation". Sagittarius, Scorpius, Libra, Ophiuchus are only up in the daytime, basking in sunlight and hidden from view. There is one summer curiosity in Ophiuchus very low in the west during the early evening hours. It’s Voyager 1, the most distant human-made object from Earth. The probe was launched on a mission to study and photograph the planets Jupiter and Saturn back on September 5, 1977. After a Saturn flyby in 1980 and a final look back for a solar system portrait in 1990, the probe began its new mission: to explore the fringes of the solar system and interstellar medium.
The sun sends a constant stream of thin, hot, electrically conducting gas into space called plasma. More commonly referred to as the solar wind, the stuff blasts across space at hundreds of miles per second. The wind forms an enormous bubble called the heliosphere that extends billions of miles beyond the farthest planets and asteroids. Near the boundary of the heliosphere, the gas slows down as it begins to feel the presence of the interstellar medium, a thin soup of dust and gas between the stars. This boundary is called the termination shock.
The sun’s gravity as well as its electric and magnetic bubble called the heliosphere define its region of influence in the Milky Way galaxy. This bubble protects the Earth and other planets from many potentially dangerous cosmic rays, which are high speed particles careening around the galaxy that can damage cells and DNA. Illustration: Walt Feimar/NASA
Both Voyager 1 and its sister probe Voyager 2 have crossed the termination shock and are now within the heliosheath just a few years travel away from the outer boundary of the sun’s influence called the heliopause. Beyond the edge of the heliopause lies interstellar space. If all these terms seem a bit confusing, consider your faucet. Turn the water on full blast and watch what happens when it hits the sink basin below. You’ll notice a smooth circle of streaming water surrounded by a zone of turbulent bubbling. The area within the circle corresponds to the sun’s flowing plasma, the circle’s edge mimics the termination shock and the turbulent water beyond is the heliosheath, where the Voyagers are now.
The sun’s sphere of influence follows a pattern similar to water pouring into a kitchen sink. You’ll notice that the water suddenly slows down when it hits the termination shock boundary. So does the real solar wind, dropping from hundreds to just 30 miles per second. Photo: Bob King
Voyager 1 is currently 10.5 billion miles from the sun and traveling at 10.5 miles per second. When you consider that it takes a radio transmission traveling at the speed of light 15.6 hours to reach Earth from the probe you begin to realize how far away that little machine really is. Pluto, which has always served as a metaphor for deep distance, is considerably closer at 3 1/2 billion miles or 5.5 light hours away. Voyager 1 has enough power to continue to function and send data back until about the year 2020 by which time astronomers hope it crosses the final boundary and samples what’s between the stars. The electricity to run the instruments all these 32 years comes from the heat produced by the radioactive decay of plutonium. Heat is converted into electricity in a special generator.
The outbound paths of four spacecraft currently heading out of the solar system. To keep tabs on their distances check out this link, which has lots of additional information. More about the Voyager probes can be found in this Voyager Q&A. Credit: Wiki
While Voyager 1 holds the distance record, it and several other craft will head toward the stars after they pass through the heliopause. In the year 40,272 the probe will pass within 1.7 light years of a minor star in the Little Dipper called AC+79 3888. Voyager 2, presently in the constellation Telescopium, is headed toward another obscure star in Andromeda.
These emissaries of our civilization may outlast our species for all we know. They’re a high-tech version of a message in a bottle. Each carries a gold record and playback stylus containing music, greetings and sounds of Earth should any extraterrestrials happen upon them.
The probes have made many discoveries about the fringe of the solar system during their long journey. Most recently the Voyager probes discovered a strong magnetic field in a nearby cloud of interstellar matter that lurks just beyond the heliopause. Click here to learn more about the find.
When I fall asleep at night I sometimes like to imagine things that continue to be active during my slumbers like a favorite river or waterfall or the slow vaporization of Mars’ north polar cap under the spring sun. It’s fun and oddly inspiring to think about things beyond one’s immediate world . Perhaps it’s time I add Voyager 1 to that list.