The Watery Part of the Sky

The Watery Part of the Sky
SKY MAP: The Celestial Sea constellations as of 10 p.m. local time, as seen from mid-northern latitudes this time of year. Eridanus is mostly below the horizon. The constellations move up in the sky during the night, so most of Eridanus becomes visible low on the horizon by midnight.

We're now two weeks into the new autumn season and for those of us who live in the Northern Hemisphere, the days keep getting shorter and cooler, as the winter approaches.  During the mid-to-late evening hours, aside from the pumpkin-colored Mars blazing in the east, there are very few bright stars in the region that is spread across the southern skies. 

Little can be seen here when the sky is hazy or flooded with moonlight.  But on clear moonless evenings you will find some interesting constellations in this part of the sky, though their figures are all rather dim. 

This whole area can be called the "Watery" part of the sky.  It isn't really watery, of course.  It is watery in the sense that it is vague and dim, like a dark pool.  These watery constellations -- Capricornus, the Sea-Goat; Aquarius, the Water Bearer; Pisces, the Fishes; Piscis Austrinus, the Southern Fish; Cetus, the Whale; and finally Eridanus, the River -- may have commemorated a great flood of long ago.

Indeed, the first three constellations belong in the zodiac, and all members of this group have been associated with the rainy season of ancient Mideast lands.  There is also a mythological connection between these star pictures and an ancient great flood in the Tigris-Euphrates basin, which has sometimes been linked to the Deluge in Genesis. It's difficult to say for sure, because the original significance of many starry figures was lost when the Greeks recast the display with characters of their own legends.    

In Latin, Capricornus literally means, "horned goat."  You might have heard of the famous little island of Capri in Italy: its name means that it is the island of goats.  But in the old star atlases Capricornus is depicted by the figure of a Sea-Goat, combining the forequarters and head of a goat and the tail of a fish.  Indeed, it appears that in creating Capricornus, the imaginations of the ancient stargazers were working on overtime. This kind of weird creature might seem totally unintelligible to us today if we did not know the ancient myth that attempts to explain its origin.

The folklore behind Capricornus is rather amusing. Supposedly, there were some sea nymphs and goddesses having a wild picnic-party in a field one day when the mischievous god, Pan, saw them and joined in the fun. About this same time, however, a huge, ferocious monster called Typhon suddenly appeared.  To escape him, each god changed himself into an animal and fled.  However, in Pan's alarm (hence the word "panic") he jumped into a nearby river before completing his transformation into a goat. As a result, his lower extremities assumed the form of a fish!  Zeus, who just happened to be passing by, saw Pan's feat and was so amused that he decreed the perpetuation of this grotesque figure in our night sky.

It should also be emphasized to newcomers of astronomy that the currently accepted name of this constellation is Capricornus, and not Capricorn.  Principally astrologers (and some older astronomy books) use the latter for labeling the zodiacal sign of that name. But quite frankly, Capricornus is such a faint constellation, if it were not a zodiacal sign most people would not even know its name.

The fourth magnitude star, Algiedi is really a pair of stars (called Alpha 1 and Alpha 2) so widely separated that they can be easily distinguished without any optical aid.  Astronomers have discovered that each star has a small companion of its own, so when you look at Algedi you're actually seeing the combined light of four stars.  Interestingly, the two bright stars are not physically connected.  Alpha 2 is about 100 light years away, while Alpha 1 is about five times more distant.  Below Algiedi is the third-magnitude star Dabih, also a pair, though binoculars are needed to see the seventh-magnitude companion of the brighter star.  Below Dabih is a charming little trio of tiny stars: Rho, Pi and Omicron, which make for a pretty sight in binoculars. 

H.A. Rey (1898-1977) managed to turn the dim stars of Capricornus into a fairly convincing looking goat.  Although mythology tells us that Capricornus is a Sea-Goat, to most people it looks more like a roughly triangular figure, which may suggest an inverted cocked hat, or maybe a bird flying toward you.  

Or, perhaps keeping in the spirit of the watery nature of this part of the sky, some might even try to envision the south end of bikini!

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Joe Rao serves as an instructor and guest lecturer at New York's Hayden Planetarium. He writes about astronomy for The New York Times and other publications, and he is also an on-camera meteorologist for News 12 Westchester, New York.

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1 AU, or astronomical unit, is the distance from the Sun to Earth, or about 93 million miles.

Magnitude is the standard by which astronomers measure the apparent brightness of objects that appear in the sky. The lower the number, the brighter the object. The brightest stars in the sky are categorized as zero or first magnitude. Negative magnitudes are reserved for the most brilliant objects: the brightest star is Sirius (-1.4); the full Moon is -12.7; the Sun is -26.7. The faintest stars visible under dark skies are around +6.

Degrees measure apparent sizes of objects or distances in the sky, as seen from our vantage point. The Moon is one-half degree in width. The width of your fist held at arm's length is about 10 degrees. The distance from the horizon to the overhead point (called the zenith) is equal to 90 degrees.

Declination is the angular distance measured in degrees, of a celestial body north or south of the celestial equator. If, for an example, a certain star is said to have a declination of +20 degrees, it is located 20 degrees north of the celestial equator. Declination is to a celestial globe as latitude is to a terrestrial globe.

Arc seconds are sometimes used to define the measurement of a sky object's angular diameter. One degree is equal to 60 arc minutes. One arc minute is equal to 60 arc seconds. The Moon appears (on average), one half-degree across, or 30 arc minutes, or 1800 arc seconds. If the disk of Mars is 20 arc seconds across, we can also say that it is 1/90 the apparent width of the Moon (since 1800 divided by 20 equals 90).

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Joe Rao
Skywatching Columnist

Joe Rao is's skywatching columnist, as well as a veteran meteorologist and eclipse chaser who also serves as an instructor and guest lecturer at New York's Hayden Planetarium. He writes about astronomy for Natural History magazine, the Farmers' Almanac and other publications. Joe is an 8-time Emmy-nominated meteorologist who served the Putnam Valley region of New York for over 21 years. You can find him on Twitter and YouTube tracking lunar and solar eclipses, meteor showers and more. To find out Joe's latest project, visit him on Twitter.