April 09, 2008


Continuing with some of the faint, minor Southern constellations, today I will talk about one of the faintest of Ptolemy's original 48 constellations, representing the mythical cup of Apollo, the constellation Crater. Found due South in the Spring at about 40 degrees above the horizon, the cup shape of this constellation opens up toward the Northwest. In mythology, Crater is linked in a story with Corvus the crow, a bird sent by the Greek god Apollo to fetch water. The crow didn't stay on task and returned with the bowl and the snake (Hydra), hoping to blame the snake for the delay, but Apollo didn't buy it. Now the cup of water is forever out of reach of the crow and all three (snake, bird and cup) are stuck in the heavens.

Alpha Crateris is Alkes, which comes from the Arabic for wine cup and is related to the English word "alcohol" (according to Kaler). There are no other bright stars in the region, and Alkes is 4th magnitude, so this is a hard one to find, about 30 degrees South of the hindquarters of Leo. It is an orange giant in a post-Hydrogen-burning phase of its lifetime, and its motion and composition implies that it was once in the galactic bulge. The actual brightest star in the constellation by a little bit is Delta Crateris, which has no proper name. It is similar to Alkes in properties, including an unusual proper motion which places it in the halo population of the galaxy or perhaps the thick disk of older stars that surrounds the thin disk where all of the gas and dust resides in the galaxy.

Beta Crateris is the only other named star here, Al Sharas, which translates to the rib, perhaps the rib of Hydra the snake since the star is in the part of the constellation bordering Hydra. One of the few deep sky objects attainable with a 10" or larger telescope would be NGC 3981, a nice nearly edge-on spiral on the Eastern border with Corvus, about 80 million light years distant. Another nice spiral imaged with the Hubble Space Telescope here is NGC 3511, and it is about half as far away as NGC 3981. Not much else of note is tucked into this nondescript corner of the sky, at least nothing that we can see with an amateur class telescope.

Posted by Observer at April 9, 2008 08:47 PM

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