Night Sky March 2005
Thank-you to all who have taken an interest in keeping our night sky dark. After last month's column, I received several questions about who to call and ask about protecting the night skies in rural Sandoval County. The best places to start are the mayors’ offices in Albuquerque, Rio Rancho, and Bernalillo. Call your Sandoval County commissioner. Finally, keep calling the casinos. They will not easily part with their bright signs and spotlights. And, by doing your small part, the never ending star show that takes center stage each night will be protected for generations to come.
We have been taught that our solar system has nine planets, several moons, and a few thousand asteroids. Now there is Sedna. Not since Clyde Tombaugh discovered Pluto on February 18, 1930, has a discovery so shaken our belief in the nine-planet number. Sedna, discovered on November 14, 2003, is a mysterious planet-like body three times farther from the Sun than Pluto. Sedna, named for the Inuit goddess of the ocean, is eight billion miles away, in the farthest reaches of the solar system, moving in an elongated elliptical orbit.
Caltech’s Dr. Mike Brown, leader of the NASA funded search for such objects, says, "The sun appears so small from that distance that you could completely block it out with the head of a pin."
Sedna is notable for its size and reddish color. After Mars, it is the second-reddest object in the solar system. Estimates put Sedna at approximately three-fourths the size of Pluto. It's the largest object found in our solar system since Pluto.
The elliptical orbit of Sedna is unlike anything previously seen by astronomers. It resembles the orbits of objects predicted to lie in the hypothetical Oort Cloud, a distant reservoir of comets. But Sedna is ten times closer than the predicted distance of the Oort Cloud. Scientists hypothesize that a rogue star passed by the sun, nudging some of the comet-like bodies inward. In order to move these objects, the star would have been close enough to be brighter than the full moon, and it would have been visible in the daytime sky for twenty thousand years.
Sedna will be at its closest to the Earth in about seventy-two years. Even then, Sedna will be well beyond Pluto's orbit. Then it will begin its 10,500-year trip back to the far reaches of the solar system. Even at its closest approach, Sedna will not be visible without a telescope larger than most amateurs can afford.
The discovery of Sedna has called into question Pluto's status as a planet. That's what astronomers have been discussing since late last year when some members of the International Astronomical Union suggested that Pluto be given a minor-planet designation.
So, what is their reasoning for demoting Pluto? For one thing, Pluto is very small. It is six times smaller than Earth, and even smaller than seven of the solar system's moons: our Moon, Io, Europa, Ganymede, Callisto, Titan, and Triton. Because Chiron, Pluto's moon, is not much smaller than Pluto itself, some astronomers consider the pair to be a double planet. Pluto's elliptical orbit is also unusual. It is the only planetary orbit that crosses that of another planet (Neptune), and it is tilted seventeen degrees with respect to the plane of the solar system. There are more than one hundred objects smaller than Pluto now known to be orbiting outside of Neptune. Pluto may just be the largest of them.
So, is Pluto really a planet or is it more like a dormant comet, simply the largest known member of the Kuiper Belt? That's the question that astronomers will be debating for a long time.
If you had X-ray vision, you would have seen something astonishing on December 27. A huge explosion launched the brightest X-ray flash ever seen on Earth. Even from fifty thousand light-years away (halfway across the galaxy), it packed so much power that it briefly altered Earth's upper atmosphere. Researchers don't know exactly why the burst was so powerful.
The commotion was caused by a special variety of neutron star known as a magnetar. The star, named SGR 1806-20, spins once on its axis every seven and a half seconds and it is surrounded by a magnetic field more powerful than any other object in the universe. These fast-spinning, compact stellar corpses, no larger than a big city, create intense magnetic fields that trigger explosions. The blast was one hundred times more powerful than any other similar eruption ever seen. Had this happened within ten light-years of us, it would have severely damaged our atmosphere and possibly triggered a mass extinction. Fortunately, there are no magnetars close enough to worry about.
Still, scientists were surprised that a magnetar so far away could alter the ionosphere. It is estimated that the object was only twelve miles across and released more energy in a tenth of a second than the Sun emits in a hundred thousand years.
It has been said that stars are like diamonds in the sky. Scientists believe that may be true in a literal sense. The solid planets in our solar system are made mostly of silicates. A new study shows that planets around some other stars may be made mostly of carbon instead. Deep inside such worlds, where pressures are intense, carbon would make layers of diamonds miles thick. In fact, meteorites, called carbonaceous chondrites, have been found on Earth that contain small diamonds.
Carbon planets might be common near the center of the galaxy, where stars are known to contain more carbon than out here on the spiral arms where our solar system resides, some twenty-six thousand light-years from the galactic middle. Scientists know that the entire galaxy is growing richer in carbon as generation after generation of stars produce heavier elements. Who knows, as we explore beyond our own solar system, diamonds may one day lose their allure by their sheer abundance!
The Planets and the Moon
- Mercury will be low in the evening sky by mid-month. Mercury reaches its highest point in the sky on March 12. The Moon will be close to Mercury on that night, too.
- Venus disappears into the Sun's glare this month.
- Look for Mars low in the southwest sky at dawn. The waxing Moon passes south of Mars on March 6.
- Jupiter will be near Spica, rising in the evening. A one-day-past-full Moon will be a fabulous sight next to Jupiter on March 26.
- Saturn shines bright high in the southern sky at sunset. The gibbous Moon will slide past Saturn on March 19.
- The Moon is new on March 10 and full on March 25.
- The vernal equinox is the beginning of spring. It occurs at 5:34 a.m. MST on March 20, which just happens to be Palm Sunday.
E-mail your questions and comments to the author, Charlie Christmann, at firstname.lastname@example.org.