Dorado the Mahi Mahi

Dorado the Mahi Mahi
Since the heavenly flying fish (Volans) remains intact, its neighboring constellation Dorado must still be hungry. Dorado is a dolphinfish, of which mahi mahi is the most common type. The mahi mahi pursue flying fish through tropical seas, and you might imagine Dorado chasing Volans through the southern skies.

The two constellations weren't invented until the late 16th century, and neither is visible further north than 15°, so they don't have any mythology. The Flemish astronomer Petrus Plancius used observations by the navigators Pieter Dirkszoon Keyser and Frederick de Houtman to help fill in gaps in the celestial globe of the southern skies.

Stars and planetsus
Dorado is a dim constellation, but many stars in Dorado are much brighter than they seem because they're a long way away from us.

For example, Dorado's brightest star Alpha Doradus appears to as a third magnitude star. It's actually a binary system composed of a giant blue-white star orbited by a bright subgiant. The fourth brightest star in Earth's night sky is Arcturus. Yet if Alpha Doradus were as close to us as Arcturus, Alpha Doradus would outshine it.

Beta Doradus is a Cepheid variable, a type of star valuable to astronomers. Based on the understanding gained by American astronomer Henrietta Leavitt, astronomers can determine the distance to distant galaxies if they can see Cepheids there.

When observed from Earth, R Doradus appears bigger across than any other known star – except for the Sun, of course. Interestingly, it has about the same mass as the Sun, but is many times brighter and nearly 400 times greater in diameter. If it were at the center of the Solar System it would extend as far as the orbit of Mars.

Stars with planets
As of January 2017, there were four stars in Dorado with known planets. An extrasolar planet is named using the designation of its star and a lower case letter. The first planet discovered is “b”, the second one is “c”, and so on.

HD 28254 and HD 30177 are sunlike stars, though compared to the Sun they are somewhat larger, less massive and cooler. Gas giant HD 28254 b takes three years to orbit its star at about the same distance as the Solar System's asteroid belt is from the Sun.

The two known planets of HD 30177 are several times more massive than Jupiter. HD 30177 b takes about 7½ years to complete one orbit and is almost 4 AU from its star. (The astronomical unit (AU) is the Earth-Sun distance.) In Solar System terms that's between the asteroid belt and Jupiter. Further out, HD 30177 c takes around thirty years to orbit and is about where Saturn would be in the Solar System.

WASP-62's one known planet is a hot Jupiter. It's a Jupiter-sized planet and so close to its star it takes just under 4½ days to orbit once.

However the star of the Dorado show is Gliese 163, a red dwarf only 50 light years away. It has three confirmed planets and a possible fourth. All three confirmed planets are bigger than Earth. Gliese 163 b is at least ten times more massive, its mass somewhere between that of the rocky planets and that of Neptune. It takes one Earth day to orbit its star, and although a red dwarf is cooler than the Sun, that's still way too close for comfort.

Gliese 163 c is more interesting. It's also too massive to be a rocky planet, and it would be hotter than Earth. Nonetheless it might be within the star's habitable zone. Gliese 163 d is much larger than Neptune, but smaller than Saturn. It orbits its star at the same distance Earth does, but that's well out of the habitable zone of the red dwarf.

Deep-sky objects
LEDA 89996 is a splendid spiral galaxy with winding spiral arms. The arms are very bright because there's extensive star formation going on. NGC 1566 is a second face-on spiral galaxy, and it's the brightest of the Dorado Group of galaxies. It has the additional distinction of being the site of a supernova observed in 2010.

However the most prominent deep-sky object is the Large Magellanic Cloud (LMC). It's a satellite galaxy of our Milky Way and on the border between Dorado and and the constellation Mensa. The LMC is 25,000 light years wide and contains ten billion stars. A long list of deep-sky objects in Dorado consists overwhelmingly of objects in the LMC. Here are a few examples.

In a region of intense star formation lies LHA 120-N 44, a superbubble 1000 light-years across. This is giant cavity carved out of a nebula of gas and dust by the stellar winds of a cluster of young stars. It isn't empty yet for it's filled with hot gas. Our Solar System lies in what was once a superbubble. [Photo: ESO/Manu Mejias]

NGC 1850 is a compound star cluster made up of a central globular cluster and a second smaller cluster. It's surrounded by nebulous filaments that probably came from supernovae.

The Tarantula nebula (30 Doradus) is brighter than any nebula in our own Galaxy. It's lit up by a cluster of supergiant stars and if it were as close to us as the Orion nebula is, it would cast shadows.

The outer region of the Tarantula Nebula was home to supernova 1987A which caused much astronomical excitement. It was the closest supernova to Earth since the invention of the telescope and its remnant continues to be studied. At its brightest, it was visible to the unaided eye.

You Should Also Read:
Volans Flies the Southern Skies
Henrietta Swan Leavitt
Do Red Dwarfs Live Forever

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