Exotic Creatures of the Southern Sky

Exotic Creatures of the Southern Sky
The familiar constellations that tell the ancient tales of gods and heroes are still in use by astronomers. Mediterranean peoples invented these constellations, and two millennia ago Ptolemy described the 48 classical ones. But the skies around the south celestial pole can't be seen from the Mediterranean, so these constellations are more modern, the creations of explorers and dedicated astronomers. Here we'll be looking at some of the lesser known constellations of the modern 88.

Plancius, Keyser and de Houtman
We still use a dozen constellations for which three Dutchmen get the credit. Petrus Plancius (1552-1622) was a cartographer who was making a star globe. He asked Pieter Dirkszoon Keyser (c. 1540-96), a navigator, to make observations of the southern stars. Frederick de Houtman (1571-1627) also sailed with a Dutch fleet and published his own star observations on his return. Despite their contributions to mapping the sky, their histories aren't well documented and it's a matter for debate as to who did what. So all three of them receive some credit for the work.

Plancius produced his globe using observations from both navigators. Johann Bayer then included the constellations in his influential star atlas Uranographia.

I've chosen to look at seven of the constellations. You'll notice the natural history theme and in addition, something else they have in common is that they are dim constellations, the brightest stars being of the third magnitude. (The higher the magnitude number, the dimmer the star. The dimmest ones we can see with the unaided eye are sixth magnitude.)

Dorado and Volans
Dorado is sometimes translated as goldfish, but these aren't the cute little things in fish tanks. Dorado is the dolphinfish – also known as mahi-mahi – and it's a large predator. (In turn, it's the prey of humans who consider it quite tasty.) The Dutch explorers saw these fish swimming after flying fish, so sometimes Dorado is represented chasing its food Volans, the flying fish.

Most of the Large Magellanic Cloud (LMC) is located in Dorado. Both it and the Small Magellanic Cloud (SMC) are prominent features of the southern sky. They aren't clouds, they're satellite galaxies of the Milky Way. Although named for Ferdinand Magellan, the first European to describe them was Amerigo Vespucci.

Within the LMC is The Tarantula Nebula (NGC 2070). It's an enormous star-forming region, some 650 light years across. It's so luminous that if it were as close to us as the Orion Nebula is, it would cast shadows at night. Supernova 1987A appeared on the edge of the Tarantula Nebula. It was the first supernova visible to the unaided eye for about four centuries, and subject to very thorough study.

Volans contains a rare and interesting galaxy named the Lindsay-Shapley ring galaxy (AM 0644-741). It was probably created from two colliding galaxies. There's a yellow core made up of the cores of the two original galaxies, and a ring 150,000 light years in diameter made of young blue stars. The new star formation would have been the result of an expanding shock wave from the collision.

Tucana
Tucana (the Toucan) is notable because within its boundaries is most of the Small Magellanic Cloud. But it also has the second brightest globular cluster in the sky, 47 Tucanae. A globular cluster is a cluster of very old stars, usually formed at the same time, and with enough mass that gravity pulls it into a spherical shape. At 14,700 light years away, 47 Tucanae is bright enough to see with the unaided eye.

You may have seen images from a Hubble deep field where the telescope has been pointed for a long time at a small area of space in order to collect light from very distant objects. The Hubble Deep Field South was carried out over two weeks in 1998, and it focused on a region of Tucana.

Apus
Apus is near the south celestial pole, as is the constellation Chamaeleon.

Apus represents the beautiful bird of paradise with its brightly-colored plumes. When early sixteenth-century explorers brought the first specimens back to Europe, people were astonished. In the Indies the local people prized the plumage and traded the birds, having first removed the feet and wings for easier packing. So the Europeans hadn't ever seen any with feet. Apus means footless in Greek. People thought that they spent their lives floating about, drinking dew, and held up by their plumes.

There are two globular clusters in Apus. One of them is IC 4499 which seems to be younger than the other globular clusters in the region – a mere 12 billion years old.

Chamaeleon and Musca
The lizard Chamaeleon is next to a nice snack, Musca the fly. Musca was depicted on a globe in 1600 as a fly and Chamaeleon had its tongue out to catch it. But Musca also spent a few centuries of being shown as a bee (Apis) instead of a fly. It's the only constellation representing an insect.

The deep-sky object HH49/50 is located in Chamaeleon. It's a powerful outflow from an embryo star, and has a mysterious spiral structure. And there's also much more starbirth in the Chamaeleon Dark Nebulae about 500 light years away. The mass of the nebulae is equal to around half a million Suns, so millions of years into the future there should be a new star cluster forming there.

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