NGC 3242 - Jupiter's Ghost
NGC 3242 is a planetary nebula in the constellation Hydra, which was discovered by F.W. Herschel in 1787. Its declination is -19°, so it rises only
about 20° above the horizon in spring in Germany. With a brightness of +7.7mag and an apparent magnitude of 40x35", it can be seen even in a
small telescope. It was named "Jupiter's ghost" because it appears almost as large as the gas giant in the sky, but looks much paler.
The distance was not known exactly for a long time, but is now given as around 4,400 light-years using data from GAIA. Its true diameter is ~2
light-years. The nebular envelope consists of an inner and an outer region, which is adjoined by a huge halo up to 20' in diameter. The inner ring
was formed around 1,500 years ago - so it is therefore quite young. The gas in the shell has a temperature of around 11,000 Kelvin. In addition to
the inner ring, two fliers (lobes) can be seen in which the gas flows outwards very quickly.
The central star has a brightness of around 11 mag and is therefore visible even in a smaller telescope. It is a white dwarf with a temperature of
T_eff = 89,000 Kelvin, making it many times hotter than our sun and therefore 3,500 times brighter than it. Its stellar winds can reach speeds of
up to 2,400 km/s.
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Despite its low altitude, NGC 3242 offers a great view in my 20" f/3 telescope. The PN is quite bright and shines in a pale turquoise-green.
At a high magnification of V=380x many of the details described above can be seen. The inner ring is clearly visible and two bulges (lobes) can
be seen at the long ends. In addition, three brighter, small knots are also visible there. The outer halo is fainter and two pale arcs can be seen to
the right and left on the long side, but these do not reach around the entire PN.
The central star is easy to see even at a magnification of 120x.
A great object! :)
