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2019-2020: CXXX
THE DAILY ASTRONOMER
Tuesday, April 21, 2020
Remote Planetarium 17: The Constellations
Why have we retained the constellations? After all, they are the merest contrivances: configurations of stars that generally lack any true association. Modern day astronomers would no more acknowledge the constellations as legitimate than they would consult a horoscope. Why do they remain? Simple. Because we want them to remain. Humans, being prodigious creators, naturally want beautiful artistic works to adorn the world and the sky above it. Does anybody think that since we all have desk calendars, we should dismantle Stonehenge and pave over Salisbury Plain? Should we take a paint roller to the Sistine Chapel ceiling? Who wants a gray world devoid of creative brilliancy?
We want the constellation and they're here, or, at least, up there!
Whenever people discuss the origin of the constellations, they generally claim that the stars have always exercised a fascination over humans owing to their remoteness. That could very well be. Unfortunately, all of our assumptions about our remote ancestors are a meager mix of inference and speculation.
We do know that the night sky contains 88 distinct constellations: those classified by the International Astronomical Union. They are Andromeda, Antlia, Apus, Aquarius, Aquila, Ara, Aries, Auriga, Bootes, Caelum, Camelopardalis, Cancer, Canes Venatici, Canis Major, Canis Minor, Capricornus, Carina, Cassiopeia, Centaurus, Cepheus, Cetus, Chamaeleon, Circinus, Columba, Coma Berenices, Corona Austrina, Corona Borealis, Corvus, Crater, Crux, Cygnus, Delphinus, Dorado, Draco, Equuleus, Eridanus, Fornax, Gemini, Grus, Hercules, Horologium, Hydra, Hydrus, Indus, Lacerta, Leo, Leo Minor, Lepus, Libra, Lupus, Lynx, Lyra, Mensa Microscopium, Monoceros, Musca, Norma, Octans, Ophiuchus, Orion, Pavo, Pegasus, Perseus, Phoenix, Pictor, Pisces, Piscis Austrinus, Puppis, Pyxis, Reticulum, Sagitta, Sagittarius, Scorpius, Sculptor, Scutum, Serpens, Sextans, Taurus, Telescopium, Triangulum, Triangulum Australe, Tucana, Ursa Major, Ursa Minor, Vela, Virgo, Volans and Vulpecula.
In 1928, the IAU developed a formal listing of these constellations including the boundaries surrounding all of them. The image below shows the entire Orion the Hunter region colored white. Each of the 88 regions along the celestial sphere are defined by an associated constellation.
The IAU boundaries were set by Belgian astronomer Eugene Joseph Delporte (1882-1955). His work augmented that of American astronomer Henry Norris Russell (1877-1957), of HR Diagram fame (we'll get to that topic later.) Although Russell's list was comprehensive, it lacked the demarcations the IAU needed to establish their tyrannical dominion over the sky,
More than half of these eighty eight constellations were based on those compiled by Claudius Ptolemy (AD 100 - 170). He listed these forty eight in books VII and VIII of his famous work the Almagest
While his list was primarily a compilation of constellations derived from Hellenistic tradition, they were based on ancient sources: such as Sumerian and Babylonian folklore. All the prominent constellations such as Orion, Pegasus and Perseus are part of "Ptolemy's 48." So, too, are all the constellations comprising the Zodiac:
Pisces, Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpius, Ophiuchus, Sagittarius, Capricornus and Aquarius.
We can ascribe the remaining constellations to three other people:
- Petrus Plancius (1552-1622)
- Johannes Hevelius (1611-1687)
- Nicholas -Louis de Lacaille (1713-1762)
Plancius gave us many of the southern constellations such as Dorado, Tucana and Triangulum Australe, which are the Swordfish, Tucan and Southern Triangle, respectively.
Hevelius "filled in" many darker regions within the northern sky. He developed seven of the IAU's 88 constellations, all of them minor: Canes Venatici, Lacerta, Leo Minor, Lynx, Scutum, Sextans and Vulpecula.
Vulpecula the Fox: one of the seven official constellations developed by Johannes Hevelius.
Nicholas-Louis de Lacaille provided the final additions to the current constellation map. These were also southern constellations, including Mensa, Telescopium and Octans, meaning table, telescope (yes, we know you figured that out) and Octant, an old navigational instrument. Octans is the southernmost constellation and contains Sigma Octantis, the southern hemisphere's equivalent to Polaris. Sigma Octantis is quite faint (magnitude 5.4) and about a degree away from the south celestial pole.
LaCaille's planisphere containing the constellations he personally crafted in the
18th century.
While this article offered only a cursory introduction to constellation history, we hope it will lend insight into the development of the constellations that loom above us every night.
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