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Chamaeleon the Southern Stellar Lizard
Chamaeleons live in lands exotic to sixteenth-century Europeans. And although color-changing lizards are fascinating, at first glance, the constellation named for them is unimpressive. Chamaeleon is a small, dim southern sky constellation created in the sixteenth century, and lacking any associated mythology. So why does it even exist? And does it contain anything of interest?
Constellations are human inventions, and one of their functions is to help us use the night sky to navigate the Earth. When European explorers and traders sailed into southern lands, they met expanses of sky they hadn't seen before, and there were no constellations as guideposts. However celestial cartographers were keen to chart and organize the southern skies. Flemish astronomer and cartographer Petrus Plancius (1552-1622) used the observations of Pieter Dirkszoon Keyser and Frederick de Houtman to create a dozen new constellations. Natural history, rather than gods and heroes, was their main theme. Chamaeleon was one of the twelve.
The new constellations made their debut in 1597 on a celestial globe created by Plancius and Jodocus Hondius. Their first appearance in an atlas was in 1603 when Johann Bayer included them in his Uranometria. Sometimes Chamaeleon has been depicted with its long tongue aimed at a neighboring constellation Musca the Fly, another creation from Plancius.
Stars and planets
Chamaeleon is a circumpolar constellation, always visible in the night sky of the southern hemisphere. Its three main stars are Alpha, Gamma and Beta Chamaeleontis (Cha) which are all of the fourth magnitude, which isn't very bright.
Alpha Cha is about 64 light years from Earth. It appears to us as the brightest star in the constellation, but that's because it's much closer than any of the other stars. It's actually one of the least luminous stars in Chamaeleon.
There's something strange about Alpha Cha. Its temperature and brightness are those of a sunlike star burning hydrogen. Yet its light spectrum shows that it's a white giant with a helium core. That means that it's used up its hydrogen fuel, having fused it into helium. What's up? No one is sure. It's one of several puzzles associated with Chamaeleon.
Gamma Cha is the second brightest star, a red giant over 400 light years away. Thousands of years from now it will be just one degree from the south celestial pole. It's not as dim as Sigma Octanis, the star that's currently closest to the south celestial pole. Nonetheless it's still too dim to offer the navigation aid that Polaris does in the northern hemisphere.
Beta Cha would appear to us as bright as Sirius if it were at the same distance from us as Sirius is. Even at three hundred light years away, Beta Cha is still visible without optical aids.
There's some evidence of stars with exoplanets in Chamaeleon, but as of May 2017 only one had been confirmed, HD 63454. That star is about 80% of the Sun's mass and somewhat cooler and less luminous than the Sun. It's 115 light years away and the planet is a hot Jupiter. Hot Jupiters are gas giants orbiting extremely close to their stars. In this case it's more than ten times closer to its star than Mercury is to the Sun. HD 63454b circles its star so quickly that a year (one orbit) would be less than three Earth days long.
Deep sky objects
Eta Chamaeleontis Cluster
The Eta Cha Cluster is a small star cluster of about a dozen comparatively young stars. It was probably only discovered because the stars are emitting X-rays that were detected by an orbiting X-ray telescope. The oddity of this little cluster is its origin. Since stars form from large cool nebulae called molecular clouds, astronomers are puzzled that there aren't any such clouds near the cluster. Its origin remains an open question.
Cha 110913-773444 or just Cha 110913 to its friends is another puzzle. What is it? It's eight times more massive than Jupiter, but less massive than a number of exoplanets. It appears too small to be a brown dwarf because they are at least 13 times the mass of Jupiter. (A brown dwarf forms like a star, but never gets enough mass to establish nuclear fusion.) Yet Cha 110913 is surrounded by the sort of dust disk from which planets form around a star.
Cha 110913 could be a sub-brown dwarf, an object that began to form as a star does, but doesn't make it to the brown dwarf stage. Or perhaps it's a rogue planet? These are planets that have been ejected from their star systems. It's a debate that will probably run for quite a while.
The Chamaeleon Complex
This Chamaeleon Complex is not a psychological problem. It's a large star forming region about 500 light years away that contains tens of thousands of solar masses of gas and dust. It encompasses the three Chamaeleon dark clouds, Cha I, II and III, and takes up much of Chamaeleon and bits of neighboring constellations.
Dark clouds, also known as dark nebulae, are important stellar nurseries. They're opaque to visible light and when visible, it's usually because they're silhouetted against a luminous background. One feature of the complex that isn't dark is IC 2631, the brightest nebula in the Complex. It's illuminated by the star HD 97300, one of the youngest, most massive and brightest of all the stars in the region.
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