The river Eridanus is a large and faint constellation, which extends from Orion almost to the southern celestial pole. With the exception of the 0.5m bright Achernar (α Eridani, “end of the river”), it contains hardly any noticeable stars and seems very inconspicuous from North America and Central Europe.

The 3.7m bright ε Eridani is 10.5 light-years away, so it belongs to the immediate solar neighborhood. Only two more stars that are visible to the naked eye are closer to us than ε Eridani – α Centauri and Sirius. The majority of nearby stars are only visible in binoculars or a telescope. ε Eridani is a young and pretty sun-like star. Mass and diameter are about 85 percent of our Sun, the luminosity is only about one third of the solar luminosity. So far, one planet with 1.5 Jupiter masses was detected around the only 500 million to one billion years old star, and it seems to have a cloud of dust and rock similar to the solar Kuiper Belt, inside which is a space that is large enough for a complete planetary system.

ο² Eridani is also known as Keid and only 16.5 light-years away. The 4.4m bright star has an only 9.6m dim companion in a distance of 83 arcsec, which can be seen only in larger binoculars because of the difference in brightness. The companion star is the easiest observable white dwarf star. Its mass is about half the solar mass, while the diameter of 17,000 miles (27,300 km) is about twice as large as that of the Earth. It needs 8,000 years to orbit the primary star once, and is about 400 AU away from the brighter star (1 AU is the distance between Sun and Earth – about 93.2 million miles or 150 million kilometers). The dwarf star is also surrounded by a 11.2m bright, and only 0.2 solar masses heavy red dwarf star, which remains, however, invisible if you don‘t have a large telescope.

The Witch Head Nebula NGC 1909 is a dim and very large nebula. In 10 × 50 binoculars it may be barely visible under optimal conditions as a 10 × 50 arcmin large glimmer of light – Its total size is at least 1 × 3°. It is probably a reflection nebula illuminated by the bright star Rigel, but it could also be a supernova remnant. It is located 2.5° away from Rigel (β Orionis) and Cursa (β Eridani). You can give it a try if you have really dark skies.

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