Orion is a well-known constellation. He has bright stars, and he straddles the celestial equator, which puts him in prominent viewing position for both northern and southern hemisphere star gazers. He also has some bright, well-known neighbors: Gemini the Twins; Taurus the Bull; Canis Major the Big Dog; Canis Minor the Little Dog. Today, let’s look at some of his lesser-known neighbors.
I’m calling them lesser-known, because they just don’t seem to get as much attention when teaching constellations to children. They may be dimmer and harder to pick out, or they are more modern, and therefore lack the rich history of the others. On my list of lesser-known neighbors of Orion, I am including: Lepus the Hare; Eridanus the River; Monoceros the Unicorn; Fornax the Furnace.
Lepus I would rank more in the middling range of notoriety. Despite its faintness of stars, Lepus is an ancient constellation, long identified as a rabbit. Orion is supposed to have loved hunting rabbit, so here is one at his feet; although in ancient times it was also seen to be Orion’s chair. However, Lepus tends to be outshined by brighter neighbors, like Orion and the dogs.
Eridanus the River is the second-longest constellation (the longest is Hydra the Water Snake in the spring sky, below Leo) and has been seen as a river since ancient times, sometimes representing the Euphrates or the Nile. The River’s source is right west of Orion’s foot star Rigel, and from there it flows southward until it reaches its mouth near the south celestial pole. The mouth star is Achernar, a very bright star that few Northern Hemispherians get to see. For my location in mid-northern latitudes, it is faint, and winding, and chopped off by the horizon, so, Southern Hemispherians, please forgive me if it is not a lesser-known neighbor of Orion in your view.
A bit removed from Orion, being on the other side of Eridanus, is Fornax the Furnace. This is not an ancient Greek constellation, but was invented by Nicolas-Louis de Lacaille, an 18th-century French astronomer who named around a dozen constellations, usually after tools like the furnace, the chisel, the clock, or the microscope. Fornax was forged from a faint set of stars in a bend of Eridanus. He originally called it Fornax Chemica to honor the famous French chemist, Antoine Lavoisier.
And finally, on the other side of Orion, is Monoceros the Unicorn. It is a faint constellation formed in the 17th century by German astronomer Jakob Bartsch. Monoceros is a Latinized Greek word that means “one-horned.” If you like the idea of a Winter Triangle (a winter equivalent to the Summer Triangle) made up of Betelgeuse in Orion, Sirius in Canis Major, and Procyon in Canis Minor, then Monoceros is in the middle of the Winter Triangle (see image below). One thing Monoceros has going for it is that it lies along the winter Milky Way, so telescope viewers can find some interesting deep-sky objects in it.
What do you think? In your experience, are these constellations lesser-known?