Barnard’s Star and Poniatowski’s Bull

21 Jun 2017

My favourite asterism lies in Ophiuchus – the obsolete constellation, Taurus Poniatowski (Poniatowski’s Bull).

It’s a striking sight in a dark night sky – the V-shaped head of the little bull is outlined by the stars 66 Ophiuchi (mag 4.6), 67 (mag 4.0), 68 (mag 4.4) and 70 (mag 4.0), and fainter stars extend the V further north.

Naked eye, it really does resemble the real Taurus. And the little horned beast is a gorgeous sight in binoculars – its anchor stars are gloriously bright, and the background is splashed with  a multitude of fainter stars that straggle off the western edge of the Milky Way.

The constellation Taurus Poniatowski was placed in the skies in 1777 by the Polish-Lithuanian astronomer Marcin Poczobut (1728–1810), director of the Royal Observatory at Vilna (now Vilnius, Lithuania). He invented it to honour his king, Stanisław August Poniatowski, who was monarch of both Poland and Lithuania. The king was a noted patron of the arts and sciences, and the bull was a feature of his family’s coat of arms.

As the inimitable Admiral Smyth recorded in his famous book, Cycle of Celestial Objects, “It is between the shoulder of Ophiuchus and the Eagle, where some stars form the letter V, and from a fancied resemblance to the zodiac bull and the Hyades, became anouther Taurus. Poczobut was content with seven component stars, but Bode has scraped together no fewer than 80.”

But alas, like a lot of small, faint constellations created by 17th and 18th century astronomers, this little constellation did not survive. Along with such beguiling constellations as Cerberus, the three-headed monster who guarded the gates of Hades, Noctua, the Owl, and Globus Aerostaticus, the Hot-Air Balloon, the little bull was put out to pasture and its stars are now part of Ophiuchus and Serpens Cauda.

However, although Taurus Poniatowski was demolished as a constellation, the name of the little asterism remains. But whenever I look at it, I don’t see Poniatowski’s bull; I see that most enchanting of little bulls, Ferdinand.

Written by Munro Leaf and illustrated by Robert Lawson in 1936, Ferdinand the Bull is surely one of the most enchanting children’s books ever written…

“Once upon a time in Spain there was a little bull and his name was Ferdinand. All the other little bulls he lived with would run and jump and butt their heads together, but not Ferdinand. He liked to sit just quietly and smell the flowers. He had a favorite spot out in the pasture under a cork tree. It was his favorite tree and he would sit in its shade all day and smell the flowers….”

To me, the celestial Ferdinand is doing just that, wandering serenely through the glittering star field towards his cork tree, and enjoying the gorgeous sprays of stars along the way…

…The vast loose open cluster Mel 186 which encompasses the little bull’s entire head, the dazzling open cluster, IC 4665, lying just one degree northeast of beta Ophiuchi; the double star, 70 Ophiuchi (which not only is one of the sky’s most gorgeously coloured doubles, but one whose stars revolve about their common center of gravity in just 88 years – making this one of the few double stars you can see move appreciably during your lifetime); the faint little globular cluster, NGC 6426; the lovely background field sprinkled with stars.

However, most wonderful of all the stars in Ferdinand’s beautiful field is one of the most famous stars in the sky – Barnard’s Star.

Barnard’s Star is classified as an M5 V main sequence star. Like all red dwarfs, it is intrinsically a very faint object, its absolute magnitude of +13.4 corresponding to a luminosity of a mere 1,2500 Sun. Thus this tiny dim and dull-red star (apparent magnitude +9.5) may not be much to look at… but it certainly invites scrutiny because it has the highest proper motion (or apparent motion across the sky) of any charted star in the heavens… not to mention it is also the second closest star to the Sun, lying about 6.0 light years away, about 1.7 light years further than Alpha Centauri (if you take Alpha Centauri as a single system).

The incomparable E.E. Barnard first noticed the star’s nature in 1916 when comparing plates made in 1894 and 1916. He found that its annual motion is 10.29 arcseconds in a direction almost due north – meaning that it covers a quarter degree, or half a full Moon diameter, in a human lifetime.

(Were I able to time travel back and give my younger self some advice it would be: “Plot Barnard’s Star’s movement across the sky for the duration of your life.” What a tremendous life-long project to watch this little star tear across the sky at the break-neck pace of 10 arcseconds per year!)

These two images of the same area of the sky, taken about 50 years apart show the proper motion of Barnard’s Star (the bright star near the bottom of the left image, and the top of the right image). The left image was taken in the 1950s as part of the Palomar Observatory Sky Survey; the right image recently, as part of a second POSS.

Last night, I examined this wonderful little star, after which I explored the star field through which the peaceable little bull Ferdinand is strolling.

Observations

16″ f/5 Dobs at magnifications of 70x, 150x, 228x, and 333x 

10×50 binoculars

Barnard’s Star (Gliese 699)

RA 08 10 11.9   Dec -49 14 00   Mag 4.7

It is a superb observing experience to see this little star; a dim red droplet of stellar light lying in a beautiful field of stars. I sketched the star’s current position in relation to the nearby field stars as accurately as possible. Next year, I plan on returning to the field in order to sketch it again and hopefully if I sketched it accurately enough last night, see motion in just a year. And astronomy being all about patience, perseverance and time… I’ll return the following year.. and the following…

After all, Barnard’s dim little red dwarf presents us with something denied us in our short lives… the rare opportunity to witness the grand cycling of stars around the galaxy.

The it was off to look at a couple of the gorgeous doubles that make up his face: