Chapter 11 from Universe Down To Earth, © 1994 Neil deGrasse Tyson. Columbia University Press
There are 88 keys in a piano and there are 88 constellations in the sky. The 88 piano keys make music. The 88 constellations make a zoo. The tally: one insect, two crustaceans, five fishes (with a pair among them), five reptiles, nine birds, three women, twelve men (with twins among them), five canines (inclusive of a hunting duo), fourteen other mammals, five mythical-magical creatures, and thirty inanimate objects that include three boat parts, ten scientific instruments, one musical instrument, two crowns, a flat-topped mountain, somebody’s hair, and a river.
To supplement your nighttime viewing, here is some under-publicized information that a well-informed star gazer should know:
From a species point of view, the following constellations are in the record-book of celestial creatures:
|Tallest:||Camelopardalis, the Giraffe|
|Heaviest:||Hydra, the Whale|
|Smallest / Lightest:||Musca, the Fly|
|Most Poisonous:||Scorpius, the Scorpion|
|Fastest:||Pegasus, the Winged Horse|
|Prettiest:||Pavo, the Peacock|
|Ugliest:||Medusa’s snake-ensnarled bloody severed head as displayed by Perseus|
From a connect-the-dots point of view, the constellation Orion has the rare combination of large size, bright stars, and an outline that resembles the hunter he is purported to be. His neck, shoulders, waist (belt), knees, sword, and shield are all clearly defined. Unfortunately, he hasn’t much of a head—there is a big empty space above his neck. There is some controversy about whether Orion is left-handed or right-handed. Early drawings and woodcuts from the 15th, 16th, and 17th centuries show the back of Orion’s head, his rear end, and the rest of his loin-cloth-drapped body as he faces away from you. The star pattern requires that he wield his wooden battle-club with his left hand, which makes Orion the world’s largest and most famous lefty. Illustrated globes of the celestial sphere from the same period (an excellent collection may be found at the Musée National des Techniques, Paris) also depict Orion from the rear, even though the constellations are intended to be viewed from the “other side” of the sky, and thus should be drawn in reverse. More recent sketches of Orion (probably drawn by righties) show him facing you as he wields his club in his right hand.
Orion’s sword is commonly illustrated over a short string of stars that hangs from his belt and dangles between his legs. I have never hunted with a sword and club, but of all the places on my anatomy that I might carry a sword, it seems to me that between-the-legs would be low on my list. Such is the cost of connecting the dots.
The stars in Pegasus, the flying horse, are not quite as bright those in Orion, but they are just as majestic. Clearly visible are four stars of a “Great Square” that form the horse’s body. Front legs drape below it. Extending forward is a slightly bent line of stars that resembles the curve of a horse’s neck and head. You must rely on your imagination for its wings. It is not commonly discussed that Pegasus is only a half a horse. You must invoke your imagination if you wish to picture Pegasus’ rear end, because the constellation Andromeda occupies the region that would otherwise complete the horse. By coincidence of configuration, the interior of the Great Square of Pegasus is remarkably devoid of visible stars—the square is as impressive for its near-square geometry as it is for its emptiness. And unbeknownst to our empty bellied winged steed, Pegasus flies through the sky upside down as viewed by residents of the northern hemisphere.
The award for most exotic star names must go to the otherwise undistinguished constellation Libra, the Scales. Its two brightest stars are officially named Zubenelgenubi and Zubeneschamali.
The most boring constellation in the sky is no doubt Triangulum Australis, the Southern Triangle. A detailed photograph of its three brightest stars shows—you guessed it—a triangle. Since nearly any three stars in the sky form a triangle, Triangulum gets the award for the most unimaginative constellation name. To be fair to Triangulum, there are several dimmer stars in and around the triangle. But since the constellation is simply the “Southern Triangle”, these stars do not participate in the designated pattern.
The greatest stretch of the imagination occurs with Apus, in the southern hemisphere. It is a constellation with three prominent stars near the south celestial pole that is supposed to be a fully plumed bird-of-paradise.
Some stars grow in the mind. The most famous of these is Polaris, the North Star. In an informal poll I once asked passers-by, “What is the brightest star in the nighttime sky?” Three fourths of them unwittingly proclaimed, “The North Star!” Let it be known that the North Star is not even in the celestial top forty. In addition, its reputation puts it at the point in the sky that is directly over the Earth’s North Pole. In the real sky, however, Polaris is nearly one degree from the north celestial pole—about twice the width of the full moon. I do not wish to upset anybody, but in 12,000 years, due to the wobbling of Earth’s axis, Polaris will be over 45 degrees from the celestial pole. Perhaps our north star should be renamed Somewhere-near-the-pole-aris. In spite of all this, residents of the northern hemisphere should not complain. Currently, the region of sky that surrounds the south celestial pole is practically blank. The nearest star with a brightness similar to that of Polaris is over twelve degrees away.
For the record, the brightest star of the nighttime sky is Sirius (Alpha Canis Majoris) in Canis Major, the Big Dog. It is nearly thirty times brighter than the North Star and commonly depicted as the Big Dog’s eyeball. Indeed, Sirius is affectionately known as the “Dog Star”. Sirius is quite recognizable as it lurks below and to the left of Orion. Sirius is also visible from nearly the entire inhabited Earth during one season or another, but it is best viewed in December and January when it rises at sunset and sets at sunrise. A corny joke between star gazing astronomers occurs when, after hearing an unbelievable story, one asks the other, “You can’t be serious!” The response is likely to be, “No, I am not Sirius, I am Zubenelgenubi!” At the end of July, Sirius rises just before the morning Sun, as though the Sun were walking its dog into the summer sky. This annual celestial ritual thus heralds the onset of the hot-and-steamy “dog days” of August.
The appearance of Sirius just before sunrise was historically well-timed with the annual rise of the Nile River through Egypt, and thus became a harbinger of a renewed agricultural cycle. So important was (and is) the rising Nile to life in Egypt that the five thousand year old Egyptian calendar uses the appearance of Sirius just before sunrise as the first day of the year.
Sirius is actually a double star. The dimmer of the pair, now called “Sirius B” is an extremely dim degenerate white dwarf. Its existence was not telescopically confirmed until 1862, when Alvan G. Clarke, an ace observational astronomer, revealed its presence buried within the glare of “Sirius A”.
The nearest star to Earth, as conclusively established by extensive astronomical research, is the Sun. It is often quoted that the nearest star to the Sun is Alpha Centauri, the brightest star in the southern constellation Centaurus and the third brightest star in the night sky. Alpha Centauri is, however, a double star system, not a single star, and that neither star in the pair is the closest star to the Sun. That privilege goes to the dim star Proxima Centauri, which is near enough to the Alpha Centauri pair to complete an orbiting triple star system. All three stars compose the front hoof of the Centaur as he straddles the Southern Cross. At one hundred times dimmer than the detection limit of the naked eye, Proxima Centuri makes a rather demure nearest neighbor.
The constellation with the greatest hype is Crux Australis, the Southern Cross. There are songs written about it, and it appears on the national flags of Australia, New Zealand, Western Samoa, and Papau New Guinea. What they do not tell you is that the constellation is small, (it is the smallest of all 88—your fist at arms length would eclipse it entirely), and its four brightest stars outline the corners of a crooked square, or a kite. In geometric terms it is nearly a “rhombus”, (although “Southern Cross” conveys more romance than “Southern Rhombus.”) There is not even a star in its middle that could represent the center of a cross. The Southern Cross is best used as a signpost to find other, more interesting celestial objects. For example, the Southern Cross is thirty degrees north of the star-starved south celestial pole, and ten degrees south west of the titanic naked-eye globular cluster Omega Centauri. The Galactic equator, (also known as the “Milky Way”), also passes directly through its middle.
Two relatively recent additions to the celestial menagerie are the southern constellations Telescopium and Microscopium, the Telescope and the Microscope. Unlike Triangulum Australis, which is simply boring, each of these two constellations are boring and undistinguished. The brightest stars in Telescopium and Microscopium are over one hundred times dimmer than Sirius. These constellations date not from the ancients but from Abbé Nicolas Louis de La Caille of the middle 18th century. With decidedly less imagination that the ancients, La Caille identified fourteen new groups of stars from the poorly-charted southern celestial sphere. He honorably named them for the principal instruments (hardware) of the arts and sciences. As noble as all this sounds, La Caille had no excuse, and thus is never to be forgiven, for naming two of the least distinguished constellations in the heavens after two of the most important scientific instruments of our times.
A constellation that was simply too big for its neighborhood was the sprawling southern hemisphere constellation Argo Navis, or Argo the Ship. Its length spanned nearly one fifth of the entire sky. Mythology holds that this is the same ship made famous by Jason and his fifty Argonauts, who set sail from Iolchis in Thessaly to Aea in Colchis to search for the golden fleece. The disproportionate size of Argo Navis led our friend Abbé Nicolas Louis de La Caille to cut up the constellation into four smaller patterns while preserving the boat theme. Thus was born Carina the Keel, Puppis the Stern, Pyxis the Compass, and Vela the Sail.
Enduring favorites for the three quarters of the world population that live in Earth’s northern hemisphere are the Big and Little Dippers. They are officially “asterisms” which simply means that they are interesting subsets of otherwise uninteresting constellations. The Big Dipper’s seven stars form a convincing kitchen saucepan in the sky: three stars form the slightly curved handle, four stars form the pot. Incidentally, the two stars of the saucepan’s front edge are reputed to point towards Polaris, but they miss their target by nearly three degrees. Hanging off Polaris is the Little Dipper. Its handle is curved the other way when compared with the Big Dipper. It looks very much like a cauldron ladle with Polaris at the handle’s tip.
The Big and Little Dippers are actually parts of the constellations Ursa Major and Ursa Minor, the Big and Little Bear. They are reported to be rather chubby bears (as bears are wont to be) with long bushy tails that form the handles of the saucepan and ladle. But these long tails are actually part of cosmic tales because tails of terrestrial bears are only nubby stubs.
Keeping with the kitchen theme, we go to an asterism in the constellation Sagittarius. Sagittarius is a centaur-archer who is part man and part horse (the front end is the half man). In spite of this legendary description, the brightest stars bear a remarkable resemblance to a stove-top tea kettle. It is short and stout—complete with a handle and a spout. This asterism is especially revered in England because the band of light from our Milky Way galaxy appears to pass through the tea kettle’s spout. In England, they always take a spot of milk in their tea. In China, however, milk was never a popular beverage. The Chinese know the Milky Way as “Yin-hur”, or Silver River. Aside from its kitchen-accessory status, Sagittarius is deservedly famous because it contains the center of the Milky Way galaxy—located about three degrees west of the spout.
The most misidentified asterism in the sky is the Pleiades. This little bunch of seven stars has a vague resemblance to a dipper. Since it is little (your thumb held at arm’s distance would cover all visible stars) many people mistakenly call it the Little Dipper. The Pleiades is above and to the right of Orion’s missing head. In Greek legend the seven stars of the Pleiades represent the seven daughters of Atlas: Alcyone, Maja, Merope, Taygete, Asterope, Electra, and Celeno. While a simple telescope shows dozens of stars, the naked eye sees only six. Celeno is missing. To reconcile this numerical error the 4th century Alexandrian-Greek commentator Theon the Younger surmised that Celeno, which is the dimmest of the group, must have been struck by lightning.
To experienced star gazers, the constellation with the most convincing resemblance to a letter of the alphabet is Cassiopeia, queen of Ethiopia. She owes her celestial existence to five bright stars in the sky that form a “W” which, according to some legends, is her throne. The “W” is somewhat lopsided, like a chair that is ready to collapse—it is rumored that she gained weight in her later years. Cassiopeia is near enough to the “pole” star Polaris that for most of the Northern Hemisphere she never sets. At various times of the night and at various times of the year she can be found above, below, and to each side of Polaris. The “W” will sometimes be a “Σ” (the upper case Greek letter sigma), sometimes an “M”, and sometimes a “∃”. This merry-go-round behavior is not a fitting fate for a queen, but Cassiopeia once said she was more beautiful than the Nereids (the Water Nymphs). The Gods did not take kindly to this boasting and (among other things) condemned her to swing eternally around the pole.
As we will detail in the next Chapter, the constellations with the greatest irrational following are the twelve of the zodiac: Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Sagittarius, Capricorn, Aquarius, and Pisces. One is often led to believe that the zodiacal constellations are prominent in the nighttime sky. But astrologers do not tell you that Aries, Cancer, Virgo, Libra, Capricorn, Aquarius, and Pisces, are underwhelming constellations that are barely recognizable as coherent patterns in the nighttime sky. Astrologers do not tell you that the constellations are not the same size so that the Sun does not move across them at equal one-month intervals. Astrologers do not tell you that the correspondence of the zodiac with calendar months is shifted backwards by an entire constellation due to Earth’s ongoing precession on its axis. Astrologers do not tell you how much money they make from gullible people.
The fact remains: all you ever see in a clear night sky is a few thousand dots of light. If you would like to see a real menagerie, and you cannot hallucinate like the ancients, then visit your nearest zoo. You will see real (tailless) bears, real (wingless) horses, real scorpions, and no centaurs. These animals will look exactly as nature intended. And the zoo-keeper will not tell you about your financial life, home life, or love life.
Copyright © 2017 Neil deGrasse Tyson. All rights reserved.