The constellation Eridanus is located in the southern hemisphere. This heavenly river is far from the smallest object of the horizon. This or that part of it can be observed from every corner of Russia. In its area, Eridanus is sixth among other constellations. It includes many objects that are interesting for observation and study by astronomers around the world.
Short description
In its length, the constellation Eridanus is second only to the famous Hydra. It occupies almost 1138 square degrees. On this huge area there are 187 stars that can be seen in the sky without the use of special equipment.
Among the stars of the constellation Eridanus, objects of various age and size are found. Next to it are the famous Orion and the equally famous Taurus, Kit, Phoenix. The Latin name for the constellation is Eridanus , and in short - Eri .
Observation
As mentioned above, part of the celestial object can be captured from anywhere in Russia and many neighboring states. But the farther south the observation post is, the larger the portion of the constellation Eridanus will be displayed in the photo. Unfortunately, from the territory of Russia it is impossible to see the southernmost and brightest star Achernar. It should be noted that the constellation is best seen in late autumn.
History and Legends
The constellation Eridanus is considered ancient. There is no exact information about the author of the discovery of this object. It was first described by the philosopher of Ancient Greece Eudoxus in the fifth century BC. Under his name it is mentioned for the first time in the Almagest. This is a catalog of the starry sky compiled by astronomer Claudius Ptolemy in the first century AD.
There are several myths about why the constellation is called Eridanus. They are all associated with Phaeton, the son of the sun god Helios. According to ancient Greek records, the Eridanus River can be identified as the Nile, Po or Euphrates. The myth of Phaeton says that he rode on his father’s celestial chariot, but lost control. When the chariot approached the Earth, a great fire began. Then the god Zeus, to stop the catastrophe, struck Phaeton with lightning, and he fell into the river.
According to one version, the Phaeton, struck by a thunderer, died after falling into the Eridan River. The son of Helios after his death became a star in the sky. And the constellation is the very river that became its last refuge. According to another legend, the Phaeton, having lost control of the chariot, left an indelible twisting trace in the sky. It is he who is the constellation Eridanus.
Eridanus Stars
The constellation contains stars of the first magnitude, seven stars with planets, double and triple stars. Many of them are of great scientific interest. For example, 82 Eridanas is a star over six billion years old. It is much older than the Sun, although inferior to it in mass. In 2011, three planets were discovered in orbit 82 of Eridanus.
Theta Eridanus is the star of Akamar. Its name is consonant with the name of the alpha star in the constellation Eridanus. The biggest star of the object is Achernar. Translated, these words mean "end of the river." The fact is that it was impossible to observe Achernar from the territory of Ancient Greece, since it is located south. Therefore, the Greeks considered the star Akamar the end of the heavenly river.
Alpha
Achernar is the brightest and most southern star of Eridanus. In addition, it is in ninth place in brightness among other objects of the night sky. The alpha feature of the constellation Eridanus is its shape. This star rotates very quickly around its axis. Due to this, it has the shape of a flattened spheroid. Its polar diameter is approximately two times less than the equatorial. It is also the hottest and bluest star in the sky. It has an apparent magnitude of 0.445.
Achernar is a supergiant, a star of the first magnitude. It is much larger than the Sun, exceeding its mass eight times. This star is separated by about 140 light years from the solar system. Achernar discovered a satellite, its mass is equal to two solar.
Betta
Betta constellation Eridanus has two names. It was originally called Dalim. This is a word of Arab origin, it is translated as "ostrich". With three other stars (lambda and psi Eridana and tau Orion), it forms a group called the ostrich's nest. However, later this stellar asterism received a different name - Orion's Foot Bench. The star, respectively, also received another name - the Course ("footrest" in Arabic).
In contrast to Achernar, betta is the beginning of a celestial river. This is the second brightest star of Eridan. Its distance to the Earth is almost 90 light years. The course far surpasses the Sun in its physical characteristics. Its diameter is three times larger, and its mass is two and a half.
Gamma
The third planet of Eridanus is the star Zaurak. The name is of Arab origin, in translation it means "boat". This star has a magnitude of 2.95 and is visible in the sky with the naked eye. Zaurak is a red giant, that is, it has a relatively low temperature, but high luminosity (220 times more than solar). The star is located 203 light years from the Sun and exceeds its radius by more than 42 times.
What is epsilon?
This is the fifth letter of the Greek alphabet. At the same time, this is the name of the star in the constellation Eridanus, similar in its characteristics to the Sun. In the ancient documents of the XIV century, you can find the Arabic name Al-Sadir, then for a long time she did not have a generally accepted name. However, in 2015, the International Astronomical Union officially gave the star the name Ran (a sea giantess in Old Norse mythology).
Epsilon of Eridanus is located at a small (by cosmic standards) distance from the Sun - 10.5 light years. A star feature is extremely fast rotation (a complete revolution around its own axis occurs in 11 days). In addition, it has a strong magnetic field. The luminosity of Epsilon Eridanus is 30% lower than that of the sun, and its mass is less than 15%. It has been established that the star has a small cosmic age - about half a billion years.
In 2008, thanks to observations by American astronomers, two asteroid belts were discovered near Eridan Epsilon. They are located at a distance of 3 and 20 astronomical units from the star. And a year after this discovery, a planet was found in the Epsilon system of Eridan. Presumably, it is Jupiter-like, and the orbit along which it rotates around a star is very elongated. In 2015, she was given the name Egir (husband and brother of Ran in Old Norse myths).
Cleopatra's Witch Head and Eye
In the constellation Eridanus, many interesting objects for studying were discovered. One of them is the reflective nebula IC 2118. Its common name is the Head of the Witch. She got such a name thanks to her bizarre shape, in which the outline of a human profile with a hooked nose and a sharp chin is clearly traced.
The light of the bright star Rigel of the constellation Orion is reflected from the fine dust of which the nebula is composed. Its area is 1.940 square degrees. Scientists suggest the initial stages of star formation in the nebula, as indicated by the presence of compact objects in it. The Witch's Head is 900 light years distant from our system.
Cleopatra's eye is the unofficial name for the planetary nebula NGC 1535. It is a white-blue disk with two rings, in the center of which there is a 17th magnitude star. The dimensions of the nebula are relatively small, so the use of powerful equipment is required for observation.
The Eridanus Cloud is a group of 200 galaxies. Most of them are spiral and irregular; a third of the galaxies of the group are lenticular and elliptical.
Multiple Star Systems
There are many multiple star systems in the constellation Eridanus . The most interesting for observation is Omicron-2 Eridan. It has other names: Cade (translated from Arabic - “shell”) or 40 Eridanus. This triple star is located 16.5 light years from the sun.
The brightest component is 40 Eridan A. This star is an orange dwarf age of 5.6 billion years. The apparent magnitude is 4.42, that is, it can be seen in the sky without the use of special equipment. Around this star rotates a pair of 40 Eridanine Sun. It is located at a distance of 400 astronomical units from the main element of the system, making a complete revolution in about 8 thousand years. 40 Eridanus B is a white dwarf, its mass is half that of the sun. 40 Eridan C less than the sun five times. This red dwarf belongs to the group of flashing stars, that is, it is able to increase its luminosity several times.
Huge nothing
The most amazing object of the constellation is rightly considered super-hollow, which is a relict cold spot. This is a huge part of space, devoid of galaxies, stars and matter. Such objects are called voids (from the English word " void " - emptiness).
This space hole is striking in its size. Its length is almost a billion light-years in diameter. This is the largest entrance of all known. Super-hollows in the constellation Eridanus have one more feature. Not even dark matter was found in it. This is an absolute void. Scientists are still not able to open the veil of secrecy of its origin. According to one version, this entry is the place of contact of our Universe with another.