Eridanus, the River
is south of Orion and Taurus in the evening skies of December and flows further south well below our horizon. Its brightest star, Achernar, is ninth on the list of bright stars, but it is a star we cannot see, unless from Hawaii, Florida or south Texas. Only one other star in the constellation ranks brighter than third magnitude. That is Cursa, at magnitude 2.9, just three degrees to the northwest of Rigel in Orion. From this point in the heavens the river wends a long and twisted way to its terminus at Achernar. It is indeed the longest pattern in the sky, and its boundaries enclose the largest area of any of the constellations.
Phaethon lived with his mother Clymene, who told him that he was of divine birth and that his father was Apollo, god of the Sun. At school, however, Phaethon was taunted by his fellows, who demanded proof of his claims. He went to his mother, who said that if he needed to know more he must ask for his father's acknowledgement. So he travelled to the east until he came to the palace of the Sun, aloft on columns glittering with gold and precious gems. Approaching his father, the youth was welcomed, and he asked, “Give me some proof by which I may be known as yours.” Apollo replied, “My son, I confirm what your mother has told you. As further proof, ask what you will and the gift shall be yours.” Phaethon immediately asked to be allowed to drive the chariot of the Sun one day. But Apollo demurred, saying, “I have spoken rashly, for your request is not safe for you, nor for any of the gods but myself—not even for Jupiter. Yet the oath is sworn and must be kept, if you must have it so.” Phaethon was adamant, as daring but unwise youngsters are, and he was led to the stables where the diamond-studded golden chariot was ready for the dawn. Apollo admonished the youth to hold tight the reins and to steer a straight and middle course, avoiding both the southern and the northern zones. Led by the morning star, the stars withdrew.
The snorting steeds began their journey, but sensed that they were being driven by an inexperienced charioteer. They veered to the right, and the Great and Little Bears felt a scorching pain and would have plunged into the sea had they been able. The boy looked to his left and saw the reaching claws of the Scorpion: his courage failed him and he dropped the reins. The horses dashed headlong, now high, now low almost to the mountaintops, the trees and fields withering and ablaze. The deserts remain dry forever more.
Earth called on Jupiter, ruler of the gods, to deliver all from the awful scene. And Jupiter, recognizing the peril, launched a lightning bolt against the charioteer, striking him from his seat and sending him into the Eridanus, like a shooting star which marks the heavens with its brightness as it falls. Afterward, to console Apollo for the loss of his son, Jupiter placed the river in the sky.
Other associations for this river in the sky have been put forth, including a representation of the Nile, mentioned by Eratosthenes, the Greek astronomer and mathematician of the third century bc. The Tigris and Euphrates are also linked to this constellation, and even the River Jordan, the Po in Italy, the Rhine in Germany, the Rhône in France, and the Ebro in Spain. Might it not as well represent the Rio Grande, flowing south as far as any major river in the continental United States?
Except for the Alpha Centauri and Sirius systems Epsilon Eridani is the star closest to us at about eleven light years distance. As early as 1973 it was found that this star has a companion with a mass less than 0.05 that of the Sun. Separated from Epsilon Eridani by about the same distance as Saturn is from the Sun, this object may be a large planet or one of the smallest stars known.
In 1998 astronomers reported a ring of dust around Epsilon Eridani that is “strikingly similar” to the inner comet zone in the solar system and shows an “intriguing” bright region that may be particles trapped around a young planet. The research team included astronomers from the Joint Astronomy Center in Hawaii, UCLA and the Royal Observatory in Edinburgh, Scotland.
The submillimeter
image shows the emission from dust particles orbiting around Epsilon
Eridani. The dust lies mainly in a ring around the star, with
a radius of 60 Astronomical Units. The star itself was not seen,
because its small, hot surface radiates very little at submillimeter
wavelengths. On the outskirts of the Solar System, there are vast numbers of comets beyond the orbit of Pluto (40 AU) making up the “Kuiper Belt.”
Epsilon Eridani is much younger than the Sun, only about 0.5-1 billion years old while the Sun is 4.5 billion years old. It is likely that tiny dust particles around Epsilon Eridani will gradually accumulate into comets like those in the Solar System's Kuiper Belt.
The one prominent bright peak in the ring around Epsilon Eridani, seen to the lower left of the star, could be dust particles trapped in an orbit close to a planet, or (less likely) the remnants of a major comet collision. No one yet knows if Epsilon Eridani has planets, but the new image gives a clue that there may be.