Lacaille's Skies - Sciences

Lacaille's Skies - Sciences
A detail of Lacalle’s 1752 map – it included his new constellations. [Photo: Linda Hall Library]

There's a curious set of constellations in the southern skies. They don't represent exotic animals, heroic deeds, or the foibles of ancient deities. They're composed of dim and nameless stars. They depict such things as a painter's easel and a microscope. Few people would be able to pick them out in the sky, even though they're recognized by the International Astronomical Union. They were the inventions of Nicolas-Louis de Lacaille (pronounced la-KYE).

In the 18th century Lacaille surveyed the southern sky, measuring the positions of nearly ten thousand stars. However when he came to put them on a planisphere, he realized that there were gaps between the constellations. He decided to fill them with representations of the tools of the arts and sciences.

Originally Lacaille named them in his native French, but later Latinized them. He died before he could finish processing his star data for a catalog. Many years later English astronomer Francis Baily carried out this task. On John Herschel's suggestion, Baily shortened all the names to one word.

Here is a quick tour of some of the highlights of the Lacaille science constellations.

Our first stop is a tribute to experimental physics. Its full Latin name Antlia Pneumatica means air pump. Lacaille pictured it as a single-cylinder pump like the one 17th century physicist Denis Papin used for his early vacuum experiments.

Although M57, the Ring Nebula in Lyra, is what people think of, Antlia also has a ring nebula (NGC 3132) and it's both brighter and more complex. Ring nebulae are planetary nebulae, created when dying sunlike stars lose their outer layers.

But the loveliest object in Antlia is the spectacular grand design spiral galaxy NGC 2997. A grand design galaxy has prominent, well-defined spiral arms. [Photo credit: ESO]

Fornax Chimiae is a chemist's furnace. (Later chemists would use a Bunsen burner.) Some sources maintain that it was created in honor of Antoine Lavoisier, one of the founders of modern chemistry. However at the time the star chart was first published, Lavoisier was only thirteen. Interestingly, in later years Lavoisier was a student of Lacaille's at Mazarin College.

Fornax is lacking bright stars, but there's no shortage of galaxies. The Fornax Cluster has at least 55, and the Fornax dwarf galaxy is part of the Local Group that includes the Milky Way.

Another notable galaxy is the spiral galaxy NGC 1097, discovered by William Herschel in 1790. Since 1992 three supernovae have been discovered there. It's also a Seyfert galaxy, a galaxy with a bright nucleus and active supermassive black hole. Although it's 45 million light years away, it's bright enough to see in medium-sized amateur telescopes.

There are some extremely distant galaxies that were revealed in the Hubble Ultra Deep Field. The most distant – and therefore oldest – is UDFj-39546284 which formed around 380 million years after the Big Bang. It's probably not a fully-fledged galaxy, but some kind of stellar structure.

Microscopium represents an early compound microscope. There isn't much of interest here, so we'll not stop long. Its brightest star Gamma Microscopii is luminous, but 229 light years away on Earth, so it's quite dim to us. But if we'd been on Earth 3.8 million years ago, this star was only six light years away. It would have been by far the brightest star in the night sky.

Even in Lacaille's day, the telescope he depicted was old-fashioned. It was an aerial telescope of the kind Jean Dominique Cassini used at the Paris Observatory. An aerial telescope is a long refractor hung from a pole.

A quartet of interacting galaxies called NGC 6845 is located in Telescopium. It was discovered in 1834 by John Herschel. In addition, there is the Telescopium group of twelve galaxies. The brightest member of the group is NGC 6968, an elliptical galaxy. It's on a collision course with spiral galaxy NGC 6861, so in the distant future the two galaxies will merge.

An astronomer needs a clock to time the observations. And our next stop is Lacaille's tribute to his trusty pendulum clock.

The constellation is full of deep sky objects. One of them is the unusual barred spiral galaxy NGC 1512 which has a starburst ring about 2400 light years across. But nothing else in the constellation matches the grandeur of the Horologium Supercluster. It's over half a billion light years across and contains around 5000 groups of galaxies.

Our final stop is the constellation that depicts the smallest object represented in the sky. It's translated as net, but it's not a fisherman's net. It's a reticle, the network of fine lines in a sighting device. In this case, it was the reticle in the eyepiece of the telescope Lacaille used for measuring star positions. He described it in the notes to his southern star catalogue as "the little instrument used to construct this catalog."

However my favorite object is NGC 1313. It's a starburst galaxy, meaning that it has a high rate of star formation. Although a barred spiral, it's a rather malformed one with an off-center axis of rotation. Appropriately, it's known as the Topsy Turvy Galaxy.

You Should Also Read:
Nicolas-Louis de Lacaille
Full Meridian of Glory - book review
Lacaille's skies – Arts

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