Some Light Science Reading. The Constellations: Libra

As first appeared in the May 2010 edition of the Syracuse Astronomical Society newsletter The Astronomical Chronicle (PDF).

Constellation Map generated with Starry Night Pro 6.

It is only fitting that, as we approach Summer and the unbelievable wealth of binocular and telescope objects that reside within the central region of the Milky Way, we spend at least one article on an otherwise mundane (to the amateur astronomer, anyway) Constellation. We endeavor this act of balance in the presentation of night sky viewing (and in the interest of accounting for all of the sky by the time these articles are done) by featuring Libra, The Scales.

The history of Libra in Western culture is one of science, religion, theft, imminent domain, here-say, and whatever existed as copyright in the Roman days (it is tough to make a Constellation associated with the Law interesting enough for prime time TV, as the only thing there is to murder is the presentation of any historical interpretation attributed to it). The reference to this collection of stars as a balance is reported to go as far back as the Sumerians (approximately 2000 B.C.), where this collection was known as “ZIBBA AN-NA”, or the “balance of heaven.” It is of particularly humorous irony this month that the Greeks were responsible for the disappearance of “the balance” from the night sky in favor of over-inflating the magnitude of the already important constellation Scorpius (for historical perspective, this article is being written as Greek economic infrastructure is falling apart faster than the Parthenon during the Siege of Athens in 1687 by Francesco Morosini, the Doge of Venice [as a good Greek, I shake my fist at the Gods in anger]).

The Romans saw fit to either return to the Sumerian tradition or simply declaw Scorpius, as Libra once again became a set of Scales. It is fate that the pinchers of an arthropod would be returned to the type of covering for reptiles. With the first publications of Libra-friendly star groupings and names upon the demotion of the now more diminutive Scorpius, one might even argue that the pen is mightier than the claws.

When not being visually accosted by rock n’ roll advertisements for lawyers behind cheap bookcase backdrops offering beaucoup bucks for your injury settlements, the legal profession often seems quite dull and arcane in its own right (sorry, Ray). Libra is equally subdued in its presentation, offering no Messier Objects within its official borders and no other really “interesting” things observable through binoculars or small telescopes. Perhaps the most interesting aspect about the constellation itself is its identification as the only inanimate object of the Zodiac, the ring of Constellations that encompass the ecliptic, or the apparent path of the Sun throughout the year.

That is not, however, to say that there isn’t anything worth its weight in hydrogen residing within the Libra boundaries. If we perform a considerable zooming in just above Zubeneschamali (phew! That translates to the “northern claw,” just as its counterpart Zubenelgenubi translates to the “southern claw.” These names would indicate that Arab astronomers opted to use both Greek and Roman sources despite the obvious conflict in the star groupings), we can see (with very good scopes) the star Gliese 581 (shown below), home of one of the most populated planetary systems yet discovered (although it is important to remember that this number is only of those planets we can detect, which means those with significant gravitational influence on their stellar anchor). This is marked “1” in the opening image. To date, there are four detected stars around Gliese 581 (note that the star name is always first, followed by a letter designation), including Gliese 581 b, a Neptune-sized object with a 5.4 day orbit, c, a rocky Earth-like planet within the Gliese 581 Habitable Zone 1.5 times wider and 5 times more dense than our own, d, a planet 1/2 as massive as Uranus and still within in the Habitable Zone, and e, a planet 1.6 times as massive as Earth and the smallest yet identified. the star Gliese 581 not only represents a feat of mathematical prowess on the part of Terran researchers, but is also of specific interest because of the number of planets within its Habitable Zone, the region within which conditions are believed to be similar to our own (specifically, liquid water on the surface). Some even refer to this as the “Goldilocks Zone,” where it’s not too cold and not too hot. One might say that this region is where a proper balance of hot and cold is reached…

Gliese 581

Of all of the asterisms (groups of stars that are not designated as Constellations but that still have specific meaning. For instance, the Big Dipper is an asterism within the Constellation Ursa Major) that have jumped out at me during my binocular viewing adventures, the one marked by the “2” is perhaps the one that most stood out to my eyes. It is one of the most perfect isosceles triangles in the nighttime sky and is reasonably clear around it such that only this shape stands out in low-power optics. When it’s out, I always look for this small golden nugget residing within the Zubeneschamali-side of the scales, tipping the balance towards the arrival of the Summer constellations Scorpius and Sagittarius, the pair that mark the inside of our own galaxy and where a disproportionate number of Messier riches abound.

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