Constellation Data

Name: ERIDANUS Translation: River Abbreviation: Eri Genitive: Eridani Size: 6 Regions: Equatorial, Southern Located Between: Hydrus, Doradus, Horologium, Fornax, Lepus, Orion RA: 3 hours Decl: -30 degrees Season: Fall Midnight Culmination: November 10 Pages where ERIDANUS is discussed in Chet Raymo's 365 Starry Nights: 217

What is the Genitive form? What is Right Ascension (RA)? Is this constellation ever visible from my latitude? What is Declination? Where should I look for a constellation on a date before or after its midnight culmination? What is Midnight Culmination?

Skylore

The Nile to the Egyptians, the Po to Italians, and the Yellow River to the Chinese.

The ancient astronomer Hipparchos (ca. 150 B.C.) called Eridanus the "River of Orion."

Description

The River Eridanus flows northward (like the Nile) from the bright star Achernar (Arabic for "End of the River") to Kursa (beta-Eridani) near Rigel in Orion. Eridanus is the longest (not largest) constellation, spanning over 50 degrees of declination, and its many faint stars glitter like reflecting light off the surface of its waves.

Legend: In the constellation chart above...
• Star colors represent their spectral types (even for double stars).
• Bright star labels are yellow; significant other stars are labelled in magenta.
• The size of each star indicates its relative magnitude.
• Constellation names are light blue.
• Grid lines represent either 10 degree intervals of declination above or below the equator, or intervals of one hour (=15 degrees) of right ascension (measured along the equator).
• Messier object numbers are pink.
• Galaxies are ovals: blue if spiral, yellow if elliptical, light blue if irregular.
• Globular clusters are gold starbursts.
• Open clusters are dotted white circles.
• Planetary nebula are green diamonds.
• Bright nebula are magenta squares.
• Dark nebula are grey rectangles.
• Green x's are x-ray sources.
• Purple O's with a diagonal slash through them are quasars.

Special Stars

Achernar, alpha-Eridani, is the 10th brightest star, but is not visible from most of the United States. No brighter star than Achernar is closer to the south celestial pole, which lies midway between Achernar and Crux the Southern Cross. Distance: 85 LY. Apparent magnitude: 0.5. Declination: -57 degrees south.

Kursa (beta-Eridani). Distance: 100 LY. Apparent magnitude: 2.8. Declination: -05 degrees south (near Rigel).

Epsilon Eridani is one of two nearby stars that resemble the Sun. Perhaps it also is surrounded by planets! (The other is Tau Ceti in Cetus the Whale.) Distance: 10.7 LY. Apparent magnitude: 3.7. Declination: -10 degrees south.

Table of 25 Brightest Stars.
What is apparent stellar magnitude?

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