While the bright part of the nebula is of about 65 arc seconds in diameter (more accurately, the `cork' is about 42x87", the `wings' 157x87"), this nebula is surrounded by a faint halo covering a region of 290 arc seconds in diameter (Millikan, 1974); this material was probably ejected in the form of stellar winds from the central star when it was still in the Red Giant phase of evolution. Today the central star is of mag 16.6 and a high temperature of some 60,000 K, which will probably cool down as a white dwarf over the coming tens of billions of years.

As usual for planetary nebulae, M76's visual magnitude is much brighter (9.6 according to Don Machholz' personal estimate, 10.1 according to Hynes; the present author thinks this is close to his own perception) than photographically (most sources agree on 12.2 mag photographically). This is due to the fact that most visual light is emitted in one spectral line, the green 5007 Angstrom forbidden line of doubly ionized oxygene, [O III] (see our Planetary Nebulae page).

As is not unusual for planetary nebulae, the distance is poorly known, with estimates between 1,700 and 15,000 light years (the latter value is from Kaufmann's Universe; Kenneth Glyn Jones has the value of 8,200). Accordingly, the true dimensions of the cork is between 0.34x0.72 and 3.1x6.4 light years, while the wings extend up to between 1.3 and 11.3 light years, and the faint halo reaches out to between 2.4 and 21 light years. (Our 3400 light years yield 0.68x1.44, 2.6, and 4.8 light years, while with Kenneth Glyn Jones' distance, the cork is 1.7x3.5, the wings 6.2, and the extensions 11.5 light years).