Now that spring is finally here, lets look at some spring constellations. It's been 5 years since I looked at the constellations of spring (The Skies of Spring, May 1996). Then I looked at Leo, Virgo, Coma Berenices and Boötes. This time I'll head south to three very interesting constellations: Hydra, Corvus and Crater.
First lets take care of two other southern constellations. Sextans is a sextant, made of dim stars, which I eliminate from the monthly star chart for lack of space. Antlia the air pump is also another dim constellation. Both are relatively modern constellations which were invented to fill rather barren parts of the sky. Modern astronomers have turned constellations from dot to dot depictions of fanciful objects and beings to areas of sky with defined boundaries. In some cases like Hydra, it took a great deal of gerrymandering to get all the stars of a constellation into a single area.
From the shape of Hydra, its easy to tell its a snake. More specifically, Hydra is a water snake. There are two other snake like constellations. There's Serpens the serpent, whose head is already rising in the east. It's a two part constellation, held in the middle by Ophiuchus the serpent bearer. Then there's Draco, a very Chinese type dragon in the north.
It is my contention that sometimes Hydra and Draco are confused. The symbol for the crossing point of a solar system object's orbit heading north, be it planet, asteroid and comet, and the plane of the earth's orbit is called the ascending node an is denoted by this symbol (W) called the dragon's head. The descending node uses the same symbol upside down, called the dragon's tail. Draco is nowhere near the ecliptic, the plane of earth's orbit in the sky. Hydra however is close to it at two points, its head and tail.
Corvus is a crow. The shape of the constellation, at least how most connect the stars isn't very crow like, the odd box shape is quite distinctive and easy to spot. Crater is a cup. It is a Latin name. It is also used to describe those cup shaped depressions on the moon.
There is a story that relates Hydra, Crater and Corvus which comes from Greek mythology. It seems the god Apollo had a pet crow. Crows are very intelligent birds, and back then, according to the story, they were white.
One day Apollo was thirsty and sent the crow to fetch him some water. Apparently crows were larger and stronger back then. On the way the crow spied an unripe fig, and stopped and waited around for it to ripen. After eating the fig, the crow realized that he was several days tardy. He found a cup, and filled it with water, then snatched up a snake and flew back to Apollo and concocted a story that the snake had kept him from reaching the water all this time. Apollo didn't believe a word of it, and punished the crow and all crows by turning him black.
Let's look at the stars of the constellations themselves. the brightest star in Hydra is Alphard which means the Solitary One. Alphard is 2nd magnitude and all the rest of the stars around it are very dim. The star also has the name Cor Hydrae. According to Burnham's Celestial Handbook it means Dragon's Heart. This goes with my comments earlier about Hydra and Draco.
Hydra's head is a group of 6 stars in a distinctive shape. It's where to start in trying to trace this constellation. The northernmost star of the hear, or of Hydra itself for that matter is the star designated Epsilon (e) Hydrae. It is a quadruple star. The main two stars are almost two close to separate, 3rd and 5th magnitude respectively less than a third of a second of arc apart. There's an 8th magnitude star 3 seconds of arc to the west, and a 12th magnitude star 19 seconds of arc to the south.
The most interesting star in Corvus is at the upper left corner of the box, which has the name Algorab. It also has the designation Delta (d) Corvi It is a very nice double star. The Stars are 3rd and 8th magnitude respectively and are separated by an angle of 24 arc seconds separation. They give a slight color contrast. The brighter star is white while the dimmer one is yellow to orange.
Northeast of this star is the famous M104, the Sombrero Galaxy, a wonderful edge on galaxy.
The large and bright spring constellations of the north aren't the only constellations worth looking at in spring. Hydra, Corvus and Crater lend their stars and stories to the richness of the spring skies.
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