Jimmy Westlake: Poniatowski’s bull
August 1, 2016
There was a time when you could go outside and invent your own constellation and, if it caught on with enough people, you could achieve a sort of immortality in the stars.
Not so anymore. While there is no law to prohibit you from connecting the stars into whatever pattern that you fancy, our modern day constellations are more or less written in stone out of a matter of scientific necessity.
By the 1920s, there were literally hundreds of star patterns that filled the sky and different folks in different parts of the world imagined different pictures in the stars. It became so difficult for astronomers to communicate with each other about the constellations that they decided it was time to agree on which of the hundreds of constellations would become permanent fixtures in our night sky and be recognized officially across the world.
When the dust settled, 88 constellations remained, including the 48 original Greek constellations and 40 more recent additions. Dozens of others were cast into the trash bin of history to be forgotten.
One such discarded constellation, Poniatowski's Bull, shines down in our late summer sky. Polish astronomer Marcin Poczobutt invented this star pattern in 1777 to honor his king, Stanislaus Poniatowski, ruler of Poland between 1764 and 1795. It was always a good idea to flatter your king, especially if you needed funds for something like a new telescope for the royal observatory.
Poczobutt confiscated a few stars from the classical summer constellations of Ophiuchus and Aquila to create his new constellation. The distinctive V-shaped group of stars that forms the face of this summertime bull bears a striking resemblance to the more familiar face of our wintertime bull, Taurus.
It's easy to spot, not far from the bright Summer Triangle star Altair and on the western side of the Great Rift in the summer Milky Way.
The stars of Poniatowski's Bull were once thought to form an actual star cluster, similar to the famous Pleiades, but it turns out to be a chance alignment of unrelated stars, more similar to the famous little Coathanger asterism. Sweeping this area with binoculars, though, will reveal several real sparkling star clusters nearby.
Slightly off of the right tip of the V of Poniatowski's Bull is one of the most remarkable stars in the sky, a faint little red dwarf star named Barnard's Star, after its discoverer, American astronomer E. E. Barnard. Shining from only six light years away, Barnard's Star is the second closest star to our solar system, after the Alpha Centauri system, but it is such a low-wattage bulb that it is not visible to the naked eye or even in binoculars.
What makes Barnard's Star unique is its rapid proper motion across the heavens relative to the surrounding stars. It moves about 10 seconds of arc per year across our line of sight, which adds up to about one-half the apparent diameter of the full moon in a human lifetime.
If the ancient Greeks had been able to see this faint star, they would have found it a whopping 7 degrees, or 14 full moons, from where we see it today. Barnard's Star has the largest proper motion of any other star.
In 1920, the stars of Poniatowski's Bull were re-annexed into Ophiuchus, the Serpent Bearer, but the little summertime bull is not forgotten.
Professor Jimmy Westlake teaches astronomy and physics at Colorado Mountain College’s Alpine Campus. His “Celestial News” column appears weekly in the Steamboat Today newspaper. Check out Jimmy's astrophotography website at http://www.jwestlake.com.