The constellation Eridanus is located in the southern hemisphere. This heavenly river is far from the smallest object in the sky. This or that part of it can be observed from every corner of Russia. In terms of area, Eridanus ranks sixth among other constellations. It includes many objects of interest to observe and study by astronomers around the world.
Short description
In terms of its length, the constellation Eridanus is second only to the famous Hydra. It occupies almost 1138 square degrees. There are 187 stars in this huge area, which can be seen in the sky without the use of special equipment.
Among the stars of the constellation Eridanus there are objects of different age and size. Next to it are the famous Orion and no less famous Taurus, Whale, Phoenix. The Latin name of the constellation is Eridanus, and abbreviated as Eri.
Observation
As mentioned above, a part of a celestial object can be captured from anywhere in Russia and many neighboring states. But the further south the observation point is, the larger the area of the constellation Eridanus will be displayed in the photo. Unfortunately, from the territory of Russia it is impossible to see the mostsouthern and brightest star Achernar. It should be noted that the constellation is best seen at the end of 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 ancient Greek philosopher Eudoxus as early as the fifth century BC. Under its own name, it is mentioned for the first time in the Almagest. This is a catalog of the starry sky compiled by the astronomer Claudius Ptolemy in the first century AD.
There are several myths about why the constellation is called Eridanus. All of them are associated with Phaeton, the son of the sun god Helios. The Eridanus River can be identified in ancient Greek records as the Nile, Po, or Euphrates rivers. The myth of Phaeton says that he rode his father's celestial chariot, but lost control. When the chariot approached the Earth, a huge fire started. Then the god Zeus, in order to stop the catastrophe, struck Phaeton with lightning, and he fell into the river.
According to one of the versions Phaeton, struck by the Thunderer, died after falling into the Eridanus River. The son of Helios, after his death, became a star in the sky. And the constellation is the very river that became his last refuge. According to another legend, Phaeton, having lost control of the chariot, left an indelible winding trace in the sky. It is he who is the constellation Eridanus.
Stars of Eridani
In the constellation there are stars of the first magnitude, seven stars with planets, double and triple stars. Many of them are of great scientific interest. For example, 82 Eridaniis a star over six billion years old. It is much older than the Sun, although inferior to it in mass. Three planets were discovered orbiting 82 Eridani in 2011.
Theta Eridani is the star Akamar. Its name is consonant with the name of the star alpha in the constellation Eridanus. The object's largest star 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, as it is located to the south. Therefore, the Greeks considered the star Akamar to be the end of the celestial river.
Alpha
Achernar is the brightest and southernmost star in Eridani. In addition, it is in ninth place in terms of brightness among other objects in the night sky. A feature of the alpha constellation Eridanus is its shape. This star rotates very quickly around its axis. Due to this, it has the shape of an oblate spheroid. Its polar diameter is about half that of the equatorial one. 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 by eight times. This star is separated from the solar system by about 140 light years. Achernar discovered a satellite, its mass is equal to two solar.
Betta
Betta constellation Eridanus has two names. It was originally called Dalim. This word is of Arabic origin, it is translated as "ostrich". With three other stars (lambda and psi Eridani and tau Orion) it forms a group called the ostrich.nest. However, later this star asterism was given a different name - Orion's footstool. The star, respectively, also received a different name - Course ("footrest" in Arabic).
In contrast to Achernar, the betta is the beginning of the heavenly river. It is the second brightest star in Eridani. Its distance from Earth is almost 90 light years. Course is much superior to the Sun in its physical characteristics. Its diameter is three times larger, its mass is two and a half.
Gamma
The third planet of Eridani is the star Zaurak. The name is of Arabic 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 a high luminosity (220 times greater than the sun). 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 given to a star in the constellation Eridanus, similar in its characteristics to the Sun. In ancient documents of the XIV century, one can find the Arabic name of Al-Sadira, then for a long time she did not have a generally accepted name. However, in 2015, the International Astronomical Union officially named the star Ran (sea giantess in Old Norse mythology).
Epsilon Eridani is located at a small (by cosmic standards) distance from the Sun - 10.5 lightyears. A feature of the star is an 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 Eridani is 30% less than that of the Sun, and its mass is 15% less. It has been established that the star has a small age on a cosmic scale - about half a billion years.
In 2008, thanks to the observations of American astronomers, two asteroid belts were discovered near Epsilon Eridani. They are 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 Eridani system. Presumably, it is Jupiter-like, and the orbit in which it revolves around the star is highly elongated. In 2015, she was given the name Aegir (husband and brother of Ran in Old Norse myths).
Witch's Head and Cleopatra's Eye
In the constellation Eridanus, many interesting objects have been discovered for study. One of them is reflection nebula IC 2118. Its common name is Witch's Head. She received this name due to her bizarre shape, in which the outline of a human profile with a hooked nose and a sharp chin can be clearly traced.
The light of the bright star Rigel in the constellation Orion reflects off the fine dust that makes up the nebula. 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 removed fromour system is 900 light years away.
Cleopatra's Eye is the informal name for the planetary nebula NGC 1535. It is a blue-white disc with two rings, centered on a magnitude 17 star. The dimensions of the nebula are relatively small, so the use of powerful equipment is required for observation.
The Eridani Cloud is a group of 200 galaxies. Most of them are spiral and irregular, a third of the group's galaxies are lenticular and elliptical.
Multiple star systems
There are many multiple star systems in the constellation Eridanus. The most interesting to observe is Omicron-2 Eridani. She has other names: Cade (translated from Arabic - "shell") or 40 Eridani. This triple star lies 16.5 light-years from the Sun.
The brightest component is 40 Eridani A. This star is an orange dwarf 5.6 billion years old. The apparent stellar magnitude is 4.42, that is, it can be seen in the sky without the use of special equipment. A pair of 40 Eridani BC revolves around this star. 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 Eridani B is a white dwarf with half the mass of the Sun. 40 Eridani C is five times less than the sun. This red dwarf belongs to the group of flare stars, that is, it is able to increase its luminosity several times.
Big Nothing
The most amazing object of the constellationrightly considered super-emptiness, which is a relic 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 void of all known. The super-void in the constellation Eridanus has another peculiarity. Not even dark matter has been found in it. This is absolute emptiness. Scientists are still not able to lift the veil of the mystery of its origin. According to one version, this void is the place where our Universe meets another.
