NGC 7139 - Planetary Nebula
About the planetary nebula "NGC 7139" there is almost no information available. The PN is located about 4.300 lightyears away from Earth
in the constellation Cepheus and was discovered by F.W. Herschel in 1787 despite its rather low brightness of 13.3mag.
With an extension of 75 arcseconds it appears twice as big as the planet Jupiter. If we convert the apparent size, we get a true diameter of 1.6
lightyears, which is a quite normal value for a PN. In the center a central star can be seen, whose brightness is given by GAIA with 18.9mag.
The parallax, on the other hand, has a very high error and can not be used to narrow down the distance of the PN.
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At a magnification of 200x using a UHC filter the 20 inch telescope shows a pale disk with low surface brightness. The disk is featureless and
nearly homogeneous - only a darker center is visible.
A central star is not visible even at 270x, but a very faint star with 15.5mag at the edge of the planetary nebula.
