The “Ghost of Jupiter”
A little further along the constellation Hydra, you’ll find a dying sun gently blowing its outer layers into interstellar space. The great William Herschel, who discovered this nebula known as NGC 3242, noted its resemblance in size and shape to the planet Jupiter. But if you look at it carefully, you’ll find it takes on many other shapes and patterns, including that of a logo well known to American TV viewers…
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Like many such nebulae, NGC 3242 looks in passing like the disk of a planet. Upon his discovery of this nebula in 1785, Herschel wrote, “Beautiful, brilliant, planetary disk ill defined, but uniformly bright, the light of the colour Jupiter… 1′ in diameter”.
A century later, the diligent amateur Admiral William Smyth wrote, “From its size, equable light, and colour, this fine object resembles Jupiter.”
But it may have been Robert Burnham who first referred to this nebula as the “Ghost of Jupiter”. Though to many, the greenish hue of the nebula, caused by raving-hot oxygen atoms set aglow by the dying star, makes the nebula look more like Uranus than Jupiter. See for yourself… it’s a lovely sight and well worth close inspection on a warm April night.
The “Ghost of Jupiter” deserves at least as much attention as the more famous Ring Nebula in the constellation Lyra. Like the Ring Nebula, NGC 3242 is also a planetary nebula, the last hurrah of a star that’s run out of fuel and approaches the end of its life as a white dwarf.
But at a relatively bright magnitude 7.3, NGC 3242 is at least 2 magnitudes brighter than the Ring Nebula, and not much harder to find. Look for it about 2 degrees southwest of the star μ (mu) Hydrae (see map below).
The “Ghost of Jupiter”, just south of μ (mu) Hydrae
NGC 3242 is plenty bright enough to see in 7×50 binoculars. In a telescope, it appears star-like at below 30x, but starts to take on shape and color at 100x and above. Use as much magnification as your telescope and sky allows. And try a UHC or OIII filter to bring out the contrast, especially if you live in the city.
Good sky and high magnification bring out the sublime features of this object. The oval outer shell defines the overall shape. But look closer. Inside the outer shell, you may see a curved, slightly closed inner shell, making NGC 3242 look a little like an eye. Or some say, like the logo for CBS (the Columbia Broadcasting System in the U.S.). Which is why you sometimes hear it called “The CBS Nebula”.
The nebula lies about 1,600 light years away, and spans 0.5 light years. The central star of the nebula shines at a dim magnitude 12.5. Its central core glows at 90,000 Kelvin; it will soon settle down as a slowly-cooling white dwarf.
