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NGC
7139 is a planetary nebula located in the constellation of Cepheus.
It was
discovered by Hershel in 1787, but only in 1918 it was understood it is a
planetary nebula.
Its diameter is 77” and its visual magnitude 13, while the
central star has magnitude 18.72.
This nebula has a good emission in both Ha
and OIII wavelenght and its structure is somewhat reminiscent of the more
famous nebula M27: indeed it is characterized by the presence of two bright condensations
while, on the perpendicular axis, two faint
lobes are visible.