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Hydrogen lines present are due to electron recombination as the high temperatures in the gases do not allow neutral hydrogen to remain that way for very long, and the protons marry up with free electrons in what are termed “free-bound” transitions. There are also collisionally excited lines where a free electron may pass close by to an element that has retained most of its electrons but may cause an excitation by transferring energy to the element, resulting in the excited element giving off a photon.

55). 6 light years away) enable astronomers to define the distance of whatever object they care to observe. For the amateur observer, these differences are not so crucial until one comes to observing any object. The fainter the object, the higher its magnitude number and the less chance it has of being seen, depending on the aperture of the observer’s telescope. Obviously, the larger the telescope aperture, the more light it can collect and therefore the fainter the objects that can be seen with it.

Due to the combination of circumstellar dust and peak radiative output in the infrared, most PPN are relatively faint. It is possible, though, that the orientation of the nebulae may play a part in its visibility, as a ‘pole on’ nebulae will appear brighter as the circumstellar dust shells will primarily be lost in an equatorial disk initially and the central star may peep through the thinner polar clouds, resulting in the PPN looking more star-like than those visible as mere infrared objects. The dispersal of these dust shells and the emerging central stars with their high temperatures and ionization potential indicate the PPN is becoming a full-fledged planetary nebula.