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LIBRA
The Scales
Libra - Celestial Atlas by Alexander Jamieson - 1822
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The constellation Libra was originally part of the constellation Scorpius, and represented the claws of the scorpion. It was the Romans who cut the claws off the scorpion and made them into a new constellation named Libra, which represented the scales of justice. But they didn't bother to change the names of the stars, so the two brightest stars in Libra are still called The Northern Claw (Zuben Eschamali), and The Southern Claw (Zuben El Genubi).
There is only one notable deep sky object in Libra. It is the globular star cluster, NGC 5897, located 40,000 light years away. With a magnitude of 8.53, it is a good target for a small scope.
There may not be much more entertainment for a backyard telescope in Libra, but there is something extremely important, although you won't be able to see it, even in the biggest telescopes. It is an exoplanet (a planet outside our solar system) that is very much like Earth. Scientists have been searching for exoplanets for many years, and have discovered many hundreds of them. Even the closest of these planets are so far away, however, that they cannot be directly detected by any technology currently available. But we do have the technology to detect the very subtle effects these planets have on the stars they orbit. Spectroscopic analysis of the light from these stars tells us a surprising amount about the star and the planet that is affecting it. But only if the planet is a massive gas giant many times larger than the largest of our planets, Jupiter, that has enough gravity to produce measurable effects on the star it orbits. So all the planets discovered were super-giant gas planets, that would have very little chance of supporting any kind of life as we know it.
But all that changed when scientists with the European Southern Observatory (ESO) turned their telescope toward a small red dwarf star in the constellation Libra called Gliese 581. This star is much smaller, and cooler, and dimmer than our Sun. It is cool and dim enough to allow a solid Earth-like planet to orbit very close to it - close enough to produce measurable effects on the star. And lo and behold they discovered not one, but four planets orbiting this star! And one of these planets is a solid, rocky planet only slightly larger than Earth (named Gliese 581c), circling the star within the habitable zone, where the temperature would allow the presence of liquid water. And where there's liquid water, there's a very good chance there's some form of life!
Further enhancing the prospect of life on Gliese 581c is the fact that the star it orbits is stable, so that the planet would have a stable climatic environment, crucial for the development of life. And the star has been around for billions of years - plenty of time for life to form and evolve. Xavier Delfosse, a member of the team that discovered the planet says, "On the treasure map of the Universe, one would be tempted to mark this planet with an X."
You can imagine what it would be like to live on such a planet. Instead of the harsh blinding light of a main sequence yellow star like our Sun, 93 million miles away, you would see a much larger, mellow-looking red sun in the sky, only 7 million miles away. And at that close distance, the planet would move around its sun very quickly, so that a year on that planet would last a mere 13 days. Although Gliese 581 is one of the 100 closest stars to Earth, it is still over 20 light years away. Our very fastest spacecraft would take about 17,000 years to reach it. So it's fair to say that we won't be visiting it any time soon.
But we can certainly watch, and listen. Listen especially for radio signals that would indicate the presence of intelligent life. The wheels and gears of huge radio telescopes all over the world are turning, pointing their dishes towards Gliese 581, and listening. And if you could build an optical telescope big enough, and focused it on this Earth-like planet orbiting Gliese 581, would you see another being, with another telescope... looking back?
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