Zuben el Genubi

Ken Tapping, June 17th, 2015

In the sky this week…

  • The western sky after sunset is dominated by Venus (lower and brightest) and Jupiter (higher and less bright).
  • Saturn lies low in the southeast.
  • The Moon will be New on the 16th and will reach First Quarter on the 24th.
  • On June 21st the Sun will reach the northernmost point in its yearly travels, an event we call the summer solstice.

This is the old name for the brightest star in the zodiacal constellation of Libra, “The Scales”. It is Arabic for “Southern Claw”, harkening back to when it was part of the neighbouring constellation of Scorpius “The Scorpion”. The second brightest star was also once part of Scorpius, and has the name Zuben el Chamali, “The Northern Claw”. To find them, first find Antares, a bright, orange-red star in the southern sky these evenings. The planet Saturn, amber coloured and quite bright, lies close above. Note that stars twinkle, planets don’t. If you scan from Antares to Saturn, and as far again, you will find Zuben el Chamali. Turn downward at right angles to that line, and scan as far as Saturn lies from Zuben el Chamali and you will find Zuben el Genubi. Neither is very bright.

These amazing and romantic names echo the thousands of years we have been looking at the sky. Around countless campfires our ancestors put their stories, legends and heroes in the sky. We have a sky full of constellations named after bears, lions, snakes, a scorpion, a swan, an eagle, and heroes such as Orion, Perseus and Hercules. The stars making up these constellations were either named after what part of the hero or animal they represent, or in some cases they describe a star’s colour or appearance. For example “Sirius” translates as “Sparkling One”. In dark winter skies this star lives up to its name. The naming custom is so solidly established that when we finally saw the stars of the Southern Hemisphere, we continued the tradition, so that among the southern stars we have a cross, a peacock, a fly, the various parts of the Greek hero Jason’s ship, a telescope, a microscope, an artist’s easel and even an air pump. Like their northern counterparts, very few of these constellations look even remotely like what they are supposed to represent.

There have been attempts to change the sky. One was to rename the constellations after religious symbols, and others to name them after politicians. These efforts failed. However, today we have an international organization, the International Astronomical Union (IAU), which is responsible for naming constellations and astronomical objects. This organization protects the existing names of objects and forces the naming of anything more recently discovered to be subject to international agreement. However, in the days before the IAU existed there was an attempt to come up with a more logical system. Today most stars have two names: their classical names, and names according to what is known as the Bayer System.

Johann Bayer was an astronomer whose life spanned the late 16th and early 17th Centuries. He proposed a simple scheme, using Greek letters. He called the brightest star in a constellation “alpha”, the second brightest “beta” and so on, so that “Sirius” became “Alpha Canis Majoris” – the brightest star in the constellation of “The Biggest Dog”, and “Antares” became Alpha Scorpii, the brightest star in Scorpius. Bayer’s catalogue has the advantage of immediately telling us what constellation a star lies in, and possibly which star it is. One limitation of this system is that the Greek alphabet has only 24 letters, which in many cases is not enough to fully catalogue a constellation.

The Bayer catalogue is useful and logical, but it would be a shame to lose the old star names. Seeing our mythology and history in the stars adds a charm to astronomy that other sciences, such as elementary particle physics, don’t have. So even though Alpha Librae and Beta Librae are precise, the old names of Zuben el Genubi and Zuben el Chamali are far more appealing.

Ken Tapping is an astronomer with the National Research Council's Dominion Radio Astrophysical Observatory, Penticton, BC, V2A 6J9.

Telephone: 250-497-2300
Fax: 250-497-2355
E-mailken.tapping@nrc-cnrc.gc.ca

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