Hydra represented a water snake to the ancient Greeks. Like a snake, this constellation is long, narrow, and squiggly. Hydra is the largest constellation in the sky, its form stretching about 75° across the southern sky as seen from mid-northern latitudes. The celestial snake’s “head” lies just east of the bright star Procyon, and its body extends to the east-southeast, ending just south of Spica.
Hydra holds a diverse array of telescopic targets. The constellation contains several beautiful double stars, as well as a fairly bright planetary nebula, a globular star cluster, a bright open star cluster, and a fine barred spiral galaxy. Because Hydra is so large, and because it is mainly elongated E-W instead of N-S, some of these objects are well-placed now, while some will be easier to observe next month. Therefore, I will cover the western part of Hydra this month and the eastern part in May.
The brightest deep-sky object in Hydra is M48, an open star cluster. This cluster is about 12° southwest of the stellar pentagon that is Hydra’s head. M48 is faintly visible to the unaided eye under dark skies, but you will get much better views with optical aid. A binocular will readily show the cluster, perhaps resolving a few stars. You will get the best view of M48 with a telescope at low magnification. If you have trouble finding the cluster with a telescope in this star-poor area, try locating it with a binocular first.
NGC 3242, the Ghost of Jupiter Nebula, is a nice planetary nebula about 2° south of Mu Hydrae. This planetary is bright enough to be visible with a binocular, but it is small enough that it will just look like a dim star at such low magnification. A telescope will show a round disc that is much like Jupiter in shape and size, hence the name. NGC 3242 is bright enough that you should be able to use as much magnification as the seeing conditions will allow. Any atmospheric turbulence will hinder high magnification views. If the atmosphere is steady, however, you may be able to see structure within the nebula, such as the central star and a dark ring surrounding the star.
One of the reddest stars in the sky is just a few degrees east of the Ghost of Jupiter. This star, V Hydrae, is too dim to be seen with the unaided eye, but it is easily visible with a telescope. Like other carbon stars, V Hya is a variable star. Most of the time this star is between magnitudes 7 and 9, but about every 17 years, it drops to around magnitude 12. To find V Hya, go 4° south of Nu Hya to the star 6 Hya. 6 Hya is somewhat faint, but it is visible to the unaided eye from moderately dark locations. V Hya is about 1° south-southwest of 6 Hya. Besides being very red, V Hya is a wide double star with a dim white companion. Low magnification will easily split the double.
For those who don’t have access to a telescope, Hydra is also home to a brighter carbon star called U Hydrae. This star varies from approximately magnitude 4.5–6 over a period of about 15 months, so it is dimly visible to the unaided eye throughout its brightness cycle. However, binoculars will give a better view of the color of this star, which is not quite as vivid as V Hya. U Hya is located about 4.5° northeast of Mu Hya, and about 4° northwest of Nu Hya.