Constellation of the Month: Eridanus (the River)

 

Eridanus is a large constellation in the southern evening December sky, starting at its northeastern end with its "beta" star Cursa near the star Rigel of the prominent constellation Orion and winding around, ending up much further south with the first-magnitude "alpha" star Achernar.  In spite of its size, Eridanus is rather devoid of bright stars besides Achernar, the rest being of third magnitude or dimmer.  Achernar, some 7 times the mass of our sun, is about 140 light-years away. Although technically it should be visible just above the southern horizon here in Gainesville when it crosses the meridian, in reality I cannot see it from this latitude because of trees and buildings almost inevitably blocking my view.  But growing up in south Florida...Hollywood to be exact...I was about 4 degrees further south and could see Achernar back then.  I don't recall having ever experienced a clear enough night when city lights or the moon didn't render Eridanus difficult to observe, but its occupation of a relatively large swath of the celestial sky qualifies it as my constellation of the month for December. The above drawing should make it clear why it represents a river...