Lacaille's skies – Arts

Lacaille's skies – Arts
A detail of Lacaille’s 1752 map – it included his new constellations. [Photo: Linda Hall Library]

Eighteenth century astronomer Nicolas-Louis de Lacaille (pronounced la-KYE) invented fourteen constellations to fill the gaps between the constellations of the southern sky. Based not on mythology, but on arts and sciences, they're still in use today. Although Lacaille died before he could process and publish all the observations, he was so highly esteemed as an astronomer that Francis Baily did the work 85 years later. The catalog was then published by the British Association for the Advancement of Science. Baily followed John Herschel's suggestion of cutting all the Latin names of Lacaille's constellations to one word.

Here is a quick tour of Lacaille constellations inspired by fine arts and practical arts.

Our first stop is Sculptor which represents a sculptor's studio. It's rich in deep-sky objects, and its interesting galaxies include the Sculptor Galaxy and the Cartwheel Galaxy. It's rich in deep-sky objects, and its interesting galaxies include the Sculptor Galaxy and the Cartwheel Galaxy. Caroline Herschel (1750-1848) discovered the Sculptor Galaxy, a lovely spiral sometimes called the Silver Coin Galaxy. It's a starburst galaxy, a galaxy where intense star formation is going on. The unique Cartwheel Galaxy does resemble a cartwheel. A core of older yellow stars is encircled by a ring of young blue stars. This is the result of a galactic collision about 200 million years ago. The blue stars were born in the starburst that resulted from the shockwaves of the collision. [Image: ESA/ NASA/Hubble]

From the sculptor, on to the painter. Pictor is an artist's easel and palette. It contains several stars known to have planets, including Kapteyn's Star and HD 40307. The latter has six planets, one of which may be a super-Earth in the habitable zone. Kapteyn's Star's two planets were a very exciting find in 2014. The star is only 13 light years away and Kapteyn b is in its habitable zone. Since the system is around 11 billion years old, if the planet is habitable, life had a long time to evolve.

We'll pass quickly through Caelum (SEE-lum), an engraver's chisel. The constellation has only two stars that are brighter than fifth magnitude, which means that even its brightest stars aren't visible to the unaided eye except in a dark sky. It also has few deep-sky objects.

Next stop: Circinus (SIR-si-nuss), the dividing compass used by draughtsmen and navigators. The compass, represented in its folded position, is small – there are only three smaller constellations. Nonetheless Circinus contains at least two sunlike stars with planets, and two strong X-ray sources. Circinus X-1 is an X-ray binary. A neutron star is one element of the binary, but astronomers aren't sure what its companion is. The other strong X-ray source is the Circinus Pulsar (PSR B1509-58). A pulsar is a rapidly-spinning, highly-magnetized neutron star, a neutron star being the remnant of a massive star that ended its life in a supernova explosion.

Lacaille didn't invent Triangulum Australe, but he depicted it as a surveyor's level. It made a nice grouping with the dividing compass and our next constellation Norma, the ruler and set square. Norma consisted of the stars between Ara and Lupus that Ptolemy didn't catalog, but after Lacaille's time its two brightest stars were assigned to Scorpius. However, the Milky Way runs through Norma, and it's contains many deep-sky objects. For example, the Norma Cluster is a rich cluster of galaxies. A rich cluster is one that contains thousands of galaxies.

The art of navigation is represented in Lacaille's sky. Our next stop Pyxis is the magnetic compass. It has three stars known to have planets, and a variety of deep-sky objects. The deep-sky objects include planetary nebula NGC 2818, created by a dying sunlike star casting off its outer layers of gas. Pyxis also contains the dwarf starburst galaxy Henize 2-10, which was the first dwarf galaxy to be discovered with an active supermassive black hole at the center. [Image: NASA, ESA, Hubble Heritage Team (STScI/AURA)]

In addition to a compass, an 18th century navigator might have had an octant. Eventually, the octant was replaced by the sextant, an instrument which is still in use. Lacaille's tribute to the octant was Octans. The constellation's main point of interest is that it includes the south celestial pole. Unfortunately, it doesn't match up to the northern Polaris. The star Sigma Octantis is one degree from the pole, but it's so faint that it's useless for navigation.

Our final port of call is Mons Mensae (Table Mountain), now called Mensa. It's the only constellation that commemorates a geographical feature. Table Mountain is near Cape Town, South Africa where Lacaille carried out his survey of the southern stars. It's the faintest constellation in the sky and its only notable feature is the Large Magellanic Cloud (LMC), a satellite galaxy of the Milky Way. The cloud-like appearance of the LMC is like the white cloud that is sometimes visible over Table Mountain.

You Should Also Read:
Nicolas-Louis de Lacaille
Lacaille's Skies - Sciences
Full Meridian of Glory - book review

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