01/21/22 – Ephemeris – A river in the sky, but not the Milky Way

This is Ephemeris for Friday, January 21st. Today the Sun will be up for 9 hours and 23 minutes, setting at 5:36, and it will rise tomorrow at 8:11. The Moon, halfway from full to last quarter, will rise at 9:31 this evening.

One of the more obscure constellations around is Eridanus, which depicts a river. The river starts near the lower right corner of Orion, near the bright star Rigel and flows to the right then down near the southwestern horizon, then it meanders along the horizon to the south before turning below the horizon. One has to travel to the far south to see the southern terminus of the river, the bright star Achernar. Writers over the ages have seen here the Nile and the Earth circling river Ocean of the flat earth days. Achernar is actually two stars. And the brightest was discovered to be the flattest star known, due to its rapid spin. The dimensions of Achernar A has been determined to be twice as wide across its equator than from pole to pole. It’s 139 light years away.

The astronomical event times given are for the Traverse City/Interlochen area of Michigan (EST, UT – 5 hours). They may be different for your location.

Addendum

An animation of the constellation Eridanus, which is a river that flows from Rigel in Orion to the star Achernar below our southern horizon at latitude 45 degrees north. Create using Stellarium and GIMP.

A model of Achernar by the European Southern Observatory (ESO).