THREE SPRINGS OF THE GAZELLE
by Jerry Cotey
Everyone is familiar with the Big Dipper but of course it is just part of the large constellation Ursa Major. During the summer months the bear is “standing” upright with the dipper asterism being just his hind quarters and his tail. His feet extend down to or even below the horizon depending on the date or time, so if one does not have an unobstructed view north, or if light pollution is a problem in that direction, objects in that part of the constellation will not be seen. The solution is to look at this part of the sky in the winter or spring months when it swings high overhead.
Other cultures populated the sky with their own constellations and one that is easy to visualize is sometimes called the three “springs” of the Gazelle. The ancient Arabians saw the stars of Coma Berenices as a pond. The Gazelle, being startled by Leo the Lion, jumped from the pond and left his tracks between the Big Dipper and what is now Leo Minor and the Lynx. Another version has the stars of Coma Berenices being the lion’s fluffy tail and as he switches his tail back and forth this startles the Gazelle. The tracks or hoof prints the Gazelle made as he jumped from the pond are now the two hind feet and the right front foot of our constellation Ursa Major. Each print or “spring” is marked by two stars, Alula Borealis and Alula Australis being closest to Coma Berenices the pond. The second “spring” is Tania Borealis and Tania Australis and the third, and now the front right paw of Ursa Major, is Talitha and Kappa Ursa Majoris.
I had an opportunity to observe this area on April 7 under a reasonably dark sky from a site in rural Mason County. With the exception of Porrima in Virgo the objects I looked at were all well placed, some nearly straight up, and I used 10x70 binoculars and a 130mm refractor for all of my observations.
Alula Australis and Alula Borealis are about 1.6 degrees apart and are now the left hind foot of Ursa Major. Alula Australis is an interesting binary star for several reasons. It is only 26 light years away and has an orbital period of just under 60 years, with the individual magnitudes being 4.3 and 4.8. Discovered by William Herschel in 1780 the components of this system have completed more than three revolutions since discovery. From our perspective the orbit is seen as an ellipse and at their closest, which occurred in 1995, the stars were .85” apart. They are now widening and are presently about 1.7” apart, a good test for a three inch scope under steady seeing conditions. This is one of the doubles that William Herschel monitored in an effort to observe stellar parallax. As his position changed, because the earth’s position changes with its orbit around the sun, he expected to see the brighter and what he thought was the closer star move back and forth with respect to the fainter star. Over several years of observations he did see motion but to his surprise it was orbital motion of the fainter star around the brighter. This was then the first double star whose true binary nature was determined, whose components are physically related. Both components are spectroscopic binaries and there is evidence of even more members that are part of this nearby system. If you have a chance to see this binary and have a clear shot to the south from your observing site you might want to swing your scope around to Virgo and check out the well known binary star Porrima. It’s components are also moving apart and display about the same separation of 1.7”.
On the night I observed Alula Australis with my 130mm refractor it was nearly straight up. At 129 power I could tell that it was double but it was not split. At 187 power the star was easily seen as double with dark space between the two components. One star was a bit fainter and seemed a little more yellow than the other. I then turned the scope to Porrima in Virgo. Much lower in the sky, Porrima was split at 187 power also but the view was much less pleasing. Both stars seemed the same white color and of the same brightness but were enlarged quite a lot by the poor seeing in that part of the sky.
A little less than 10 degrees to the northeast of Alula Australis is the star Groombridge 1830. Plotted and labeled on the Sky Atlas 2000 charts this star has a magnitude of 6.5 and is easily seen in binoculars. Relative to the background stars Groombridge 1830 moves about 7” per year. When discovered it had the highest proper motion of any star known but now ranks third in this regards, behind Barnard’s Star and Kapteyn’s Star. A high proper motion usually means that a star is a very close neighbor to our solar system but because Groombridge 1830 is about 30 light years away part of it’s rapid motion comes from the fact that it has a high velocity relative to the earth, about 216 miles per second. This relative motion is due in part to the fact that it is a population II star, a halo star that is not following the rotation of our galaxies disk and not traveling in the same direction as the sun. It probably formed before our galaxy had a well defined disk and could be as old as 10 billion years!
About 5 degrees northwest of Alula Australis is the star Lalande 21185. It too is shown on the Sky Atlas 2000 charts and has a magnitude of 7.6. At a distance of 8.3 light years it is the fourth nearest stellar system to the sun. A typical red dwarf star, most of its energy is emitted in the infrared. It has a diameter less than one half that of the sun and is a much cooler 3,383 K. Although once thought to have a planetary system more recent observations suggest otherwise.
About two thirds of the way between Tania Borealis and Talitha is the triple star South 598. This triple was discovered by Sir James South, a contemporary of William Herschel’s son John. Together they re-measured many of the pairs discovered by William and presented a catalog of 380 new pairs and multiple systems to the Royal Society in 1824. This is a wide triple star with magnitudes of 5.5, 7.8 and 9.7 and separations of 72” and 84”. From my observing site the star was just visible to the naked eye and the brightest two made a neat pair for the 10x70 binoculars. All three stars were visible in my 130mm refractor and together make a tiny L shaped asterism. Because they are so wide they look best at low powers.
Tania Australis, the southern-most star making the second leap of the Gazelle, is a red giant and the difference in color from its neighbor Tania Borealis is striking in a pair of binoculars. Less than a degree due west of Tania Australis is NGC 3184, a large face on spiral galaxy. This galaxy was discovered by William Herschel and was classified by him as a type I object meaning a bright nebula. It has a magnitude of 9.6 and is 7’x7’ in size although just the bright core is visible in a small telescope. In the 130mm scope this object is fairly large but very faint at 70 power. Had it not been for some bright stars nearby to help pinpoint its location I might have missed spotting this galaxy.
Another galaxy that William Herschel discovered in the area is NGC 2841. This galaxy is about 3 degrees north east of Talitha. With a magnitude of 9.3 it is 8’x3.3’ in size and like NGC 3184 is a type I object in his classification system. Both of these galaxies are on the Herschel Club 400 list. This object was obvious at 41 power and appeared as an elongated glow with a brighter nucleus at 70 power in the 130mm scope.
Talitha, the brightest star making the third spring of the Gazelle, is a double star that was first noticed by John Herschel in 1820. The primary has a magnitude of 3.1 and the secondary is somewhere between magnitude 9 and 10 depending on which source one refers to. Now separated by about 4” they were about 10” apart when discovered. On the night I made my observations the companion was not visible and I am looking forward to trying again under a darker sky.
With a small telescope or even binoculars this part of the sky holds many interesting objects, and of course with every increase in aperture the list of potential targets gets larger. If the weather-man treats us right this spring perhaps you will be able to explore the Three Springs of the Gazelle for yourself.
Clear Skies
Jerry Cotey