Alula, Tania, and Talitha
Night action awaits visitors to Michiana the weekend beginning May 6, 2016. The eighth Michiana Star Party (MSP8) offers you stillness and darkness with telescopes in Vandalia, MI. If you seek its antithesis, the Riverlights Music Festival launches with music and lights along the St. Joseph River in South Bend, IN. Either way, it will be a visual feast for rural and urban night owls alike. Whether you are in the countryside or downtown--or double dip and do both!--you can observe a few celestial targets in common.
On the Monday after that weekend, May 9, with the right gear you can witness the 2016 transit of Mercury, in which the inner planet passes directly in front of the sun. Because Mercury is visually so small and you are looking at the sun, a solar filtered telescope is required to observe the transit of Mercury safely. At the star party you can get details and meet folks who are setting up the proper equipment for the transit of Mercury.
But first, some star pair oddities. If you face north on May 6 at 10:00 p.m. and look high overhead, you can see the upside down constellation Ursa Major, the Great Bear. The Big Dipper is part of the bear's body and tail, with the two end stars pointing down to the north star Polaris. Each of Ursa Major's three depicted legs ends in a pair of stars that can be considered the bear's claws. Arabic stargazers saw these three pairs as three leaps of a gazelle. There's also a "Muscida" on the bear's nose.
If you instead face south and crane your neck backward, the constellation will appear right side up. Because Ursa Major is a circumpolar constellation, it appears to rotate around the north star Polaris, so for year-round clarity and memorization I have labeled the star pairs in this upright position.
You can think of each each star pair as having a primary name in common, then its second name is either Australis for the southern star of the pair or Borealis for the northern star of the the pair. The hind pair of stars are Alula Australis and Alula Borealis; the other hind pair are Tania Australis and Tania Borealis. While some astronomy software depicts the front pair as Talitha Australis and Talitha Borealis, Dr. Jim Kaler notes Talitha "for some odd reason...belongs exclusively to the northern of the pair."
Meanwhile, to the south, Jupiter seems ablaze at 10:00 p.m. You can't miss it.
For an all-sky perspective of what else is up that night, this monochrome chart depicts the constellations on May 6 at 10:00 p.m.
Dr. Jim Kaler describes the attributes of some of these paired stars, with excerpts below.
ALULA AUSTRALIS (Xi Ursae Majoris). Ursa Major walks on legs identified by three pairs of close but unrelated stars that the ancient Arabs called the "springs (leaps) of the gazelle" that lie north of Leo Minor. From west to east they are Talitha and Kappa UMa, Tania Borealis and Australis, and Alula Borealis and Australis, the last a bright-end-fourth magnitude (3.78) star better known as Xi UMa. The proper name comes from an Arabic phrase meaning the "first spring" ("leap" or "jump," not the season), the other two names in reverse order meaning "second spring" and "third spring" (the "Borealis" and "Australis" denoting the northern and southern stars of the pairs). Alula Australis is of profound historical interest. While Mizar was the first known "double star," our Alula was the first double to be identified as physically related (by no other than William Herschel, the discoverer of Uranus in 1781), when he saw that the two orbited each other. Xi UMa was also the first star for which an orbit was actually determined, such orbits (with gravitational theory) allowing the all-important measure of stellar mass. Alula Aust, just 27 light years away, is made of near-twin class G hydrogen- fusing dwarfs similar to the Sun: brighter fourth magnitude (4.33) class G0 Xi UMa A coupled with lesser fifth magnitude (4.80) class G5 Xi UMa B, with respective (but not well- determined) temperatures of 5740 and 5720 Kelvin, luminosities 1.1 and 0.72 solar, radii 1.04 and 0.9 solar, masses (from the theory of stellar structure and evolution) of 1.0 and 0.98 solar, and an age of 6 billion years, 1.5 billion years older than the Sun.
ALULA BOREALIS (Nu Ursae Majoris). Leaping across the sky south of Ursa Major's Big Dipper bounds the Arabic gazelle, marked by three unrelated pairs of stars, the First-Leap Alulas (Borealis and Australis, respectively Nu and Xi), the Second Leap Tanias (Borealis and Australis, Lambda and Mu), and the Third Leap made of Talitha (to the north) and Kappa (to the south). Talitha and friend lie just north of southern Lynx, the Tanias just north of Leo Minor, while the Alulas can be found just to the west of the Smaller Lion. In Greek tradition, they are the feet of the Great Bear as he plods around the North Celestial Pole. Physically, Alula Bor is a higher mass example of one of the more common kinds of naked eye stars, a class K (K3) giant, a star that has given up core hydrogen fusion and is now quietly pursuing the fusion of helium into carbon and oxygen.
TANIA AUSTRALIS (Mu Ursae Majoris). Our Ursa Major, the Greater Bear, contains remnants of ancient Arabic constellations, the best-known example the star Alkaid, which refers to the leader of the daughters of a funeral bier. Southwest of the Dipper's bowl lie three obvious pairs of stars that represent the bear's paws, but to the Arabs were the tracks of leaping gazelles. The middle pair is the "second leap," from which comes the name "Tania" (for "second"). In the multi-cultural mix of constellation lore, the northern one received the Arab-Latin name Tania Borealis, the southern Tania Australis. Bayer assigned the three "leaps" ordered Greek letters, Tania Borealis receiving Lambda, Tania Australis Mu. The two make a lovely contrast, Tania Borealis a white class A subgiant, Australis a fairly rare (for naked eye stars) red class M (M0) giant. Tania Australis shines at mid third magnitude (3.05) from a distance of 250 light years (double the distance of Borealis, the two only a line-of-sight coincidence).
TANIA BOREALIS (Lambda Ursae Majoris). Three pairs of unrelated stars mark the feet of Ursa Major, the Great Bear. To the Arabs, they marked the "leaps of the gazelle," the first, second, and third leaps proceeding from east to west. Tania Borealis (Lambda Ursae Majoris) is the more northerly of the stars that make the "Second Leap," the name from a long phrase that means just that (plus the Latin for "northern"). The southern star of the pair is Tania Australis (Mu UMa), while the first leap is made by Alula Borealis and Australis (Nu and Xi), the third from Talitha (Iota) and Kappa UMa. Positioned just north of Leo Minor, faint-third-magnitude (3.45) Tania Bor is a class A2 subgiant that lies 134 light years away, 70 percent farther than the middle five Dipper stars that make the most notable portion of the Ursa Major Cluster.
TALITHA (Iota Ursae Majoris). Three close (but physically unrelated) pairs of stars make the feet of Ursa Major, the Great Bear. In Arabic culture, the three represent the "leaps" of a gazelle, Talitha (Bayer's "Iota" star) and Kappa Ursae Majoris making (and meaning) the westernmost "third leap" (the name actually coming from the number 3). The other two "leaps," Tania and Alula, are divided into northern and southern (Tania Australis and Borealis and Alula Australis and Borealis), but for some odd reason not Talitha, which belongs exclusively to the northern of the pair. Talitha, in simplest form a cooler class A (A7) star 48 light years away, is on closer look a complex multiple.