Article Updated: 24 Dec , 2015


The southern constellation of Tucana was first introduced in 1589 by Petrus Plancius on a celestial globe which was later added to Johann Bayer’s atlas – Uranometria – in 1603. Located south of the celestial equator, Tucana spans 295 degrees of sky and ranks 48th in size. It has 3 main stars in its asterism and contains 17 Bayer Flamsteed designated stars within its confines. It is bordered by the constellations of Grus, Indus, Octans, Hydrus, Eridanus and Phoenix. Tucana is visible to all observers located at latitudes between +25° and ?90° and is best seen at culmination during the month of November.

Since Triangulum Australe is considered a “new” constellation, there is no mythology associated with it – only how its name came to be. During the late 1600s Dutch navigators Pieter Dirkszoon Keyser and Frederick de Houtman were exploring the southern hemisphere and part of their work dealt with charting the southern stars as well. Petrus Plancius, a celestial cartographer included their observations on his celestial globe, as well as their constellation names which depicted the strange creatures which they encountered on their travels. At the time it was called “Den Indiaenschen Exster”, but Plancius changed it to “Toucan”. When Johann Bayer added the constellation to Uranometria, he included it as “Tucana” and it was later adopted permanently under this name by the International Astronomical Union.

Let’s begin our binocular tour with Alpha Tucanae – the “a” symbol on our chart. Alpha is a very interesting star not just because it is a binary star, but because it is an astrometric binary star. This means Alpha’s companion has never been directly observed, either optically or spectrally, but is believed to be there because of changes in the proper motion of the primary. What happens? Every 11.5 years we pick up a precise wobble from this 199 light year distant star!

Now, turn your telescope towards Beta Tucanae – the “B” symbol. Beta Tucanae is pretty special, too. Not just because it is a binary star – but because it is a whole, six-part star system. Located about 140 light years from Earth, the Beta system consists of Beta-1 Tucanae and Beta-2 Tucanae, the two brightest stars you will see in the eyepiece. Both main sequence dwarf stars, separated by about 27 arc seconds and very close to the same magnitude. Do you see a slight color difference? Beta 1 is a blue-white B-type star while Beta 2 is a white A-type star.

Time to turn up the magnification because both of these bright stars have at least one closer main sequence companion. Located 2.4 arcseconds away from Beta 1 is the A component. At magnitude 13.5, it will require a large telescope, but what fun! Now, look at Beta 2… approximately 0.38 arcseconds you’ll find the 6th magnitude D star! Ready for more? Then move on to Beta-3 Tucanae – another binary star which is separated from Beta-1 and Beta-2 Tucanae by 9 arc minutes. Both components of the binary system are white A-type main sequence dwarfs and it’s tight.. only 0.1 separation and nearly matching in magnitude. That means two stars which orbit each other only four Earth distances apart!

For the eye, binoculars or telescope, it’s time to have a look at NGC 104 (RA 0 : 24.1 Dec -72 : 05), better known as “47 Tucanae”. With a magnitude of 4 and spanning 31 arc minutes in size, this globular cluster will blow you away! Those huge, gravitationally bound balls of stars know as globular clusters aren’t without a heart. Containing a thick concentration of 10,000 to more than a million stars in a region spanning just 10 to 30 light-years, globular clusters are more akin to seething masses of suns where the lightweights head for the outer edges while the giants collect in the core. What causes this process? Do globular clusters really have a way of getting some stars closer to the heart? What you see in 47 Tucanae, is the second largest globular cluster in the Milky Way’s busy galactic halo. As its name “47 Tucanae” implies, its core was first cataloged as a star and numbered the 47th in Tucana the Toucan – but not for long. On September 14, 1751 a French astronomer named Nicholas Louis de Lacaille was the first to discover its true nature with a half inch diameter spy glass and cataloged it as nebulous object. Next to observe and catalog it were James Dunlop in 1826, and John Herschel in 1834 when it became New General Catalog (NGC) 104. At home some 13,400 to 16,000 light years away from our solar system, this inconceivably dense concentration of at least a million stars spans 120 light years at the outside, yet at its heart is more than 15,000 individual stars that are packed so densely that you couldn’t fit our solar system between them.

Believed to have all been born about the same time from the same cloud of gas, globular clusters like 47 Tucanae are a wonderful study of how stars evolve and interact. With such busy conditions, it only stands to reason that stellar collisions have occurred at one time or another and 47 Tucanae is no exception. In the core, 23 unusually hot and bright stars called blue stragglers have been identified – the double massive result of two stars bumping into one another. Due to the associated gravitational pull, heavier stars slow down and sink to the cluster’s core, while lighter stars pick up speed and head for the outer edges. The more often collisions happen the more dramatic the results – pushing the smaller stars ever faster towards the periphery and creating exotic objects. What no earthly photo can ever show is that 47 Tucanae contains at least twenty millisecond pulsars – better known as neutron stars. Can you imagine a sun that rotates on its axis a few hundreds to one thousand times a second? Just imagine the power. According to scientists, such peculiar objects are generally thought to have a companion from which they receive matter. Close interacting binaries and bright cataclysmic binaries… dwarf novae and nova-like variable candidates…. They all make their home here closer to the heart.

Now, keep binoculars and telescopes handy we’re off to the next globular cluster – NGC 362 (RA 1 : 03.2 Dec -70 : 51). At near magnitude 7 and 12 arc minutes in size, this much smaller globular was discovered by James Dunlop on August 1, 1826. You’ll find it compact and very pretty in a smaller scope and well-resolved in large aperture. In 1980 this particular star cluster was compared to a similar one, only to find it was about 3 billion years younger!

Ready for that great big galaxy you can see without any optical aid? Then say hello to the Small Magellanic Cloud. This dwarf galaxy is part of our own local galaxy group which includes the Milky Way, Large Magellanic Cloud, the Andromeda Galaxy and more. It is believed the SMC was once a barred spiral galaxy that was disrupted by the Milky Way – and now an irregular galaxy which still contains a central bar structure. Located about about 200,000 light-years away, you’ll find a host of other great NGC objects inside as well, such as NGC 265, NGC 290, NGC 346, NGC 347and NGC 602. Enjoy!

Chandra Observatory
Chart courtesy of Your Sky.

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