The Ghosts of Cassiopeia (IC 63 & IC 59)
If you are a Northern hemisphere dweller, who is lucky enough to have clear skies on an autumn or winter night, then you can undoubtedly recognize one the most famous constellations of the Northern sky: the W-shaped Cassiopeia constellation.
Usually, but not always, when we meet a star named “Alpha” + a constellation name, for instance, “Alpha Cassiopeiae”, it means that this star is the brightest in that constellation. Hence, “Beta” is the second brightest, “Gamma” is the third brightest, and so on… In the Cassiopeia constellation, the middle star Gamma Cassiopeiae – whose magnitude varies from +2.15 (today) and +3.4 (1940) – is a variable star that can appear fainter or brighter than Beta Cassiopeiae (+2.3 magnitude), or even Alpha Cassiopeia (+2.25 magnitude). It means that Gamma Cassiopeiae at times becomes the brightest star in the constellation for a certain time.
This star is a particular variable star. It does not have a regular cycle. Gamma Cassiopeiae has a very high rotation rate (around 1.6 million km per hour), which gives it a flattened shape at the equator. Gamma Cassiopeiae even gave its name to a whole class of variable stars.
The star ejects strong wind streams in the space around it. These winds form a “decretion disk” all around the star that could explain the variations of Gamma Cassiopeia’s brightness. This disk appears as a blur around the star in this picture. This picture was taken with a ZWO ASI 183 MM -Pro Mono Cooled camera, mounted on a Skywatcher ED 80 telescope, equipped with a Black Diamond lens. We used the Baader 1,25″ H-Alpha filter and RGB Filters. The total exposure time was 15 hours.
Overall, Gamma Cassiopeiae is about 65 000 times brighter than the Sun.
Now if you look slightly around Gamma Cassiopeia (exactly at 0h 59m 34.8s right ascension and 60° 49′ 7″ declination, or 00h 56m 46.8s right ascension and +61° 04′ 07″ declination) you will meet IC 63 and IC 59, two faint ghost-shaped nebulae, also known as the Ghosts of Cassiopeia.
While you can meet IC 59 on the northern side of Gamma Cassiopeiae, you will find IC 63 to the northeastern side of the star. Both nebulae are about 610 light-years apart. The distance between the nebulae and the star is about 3 light-years only. Because IC 63 is slightly closer to Gamma Cassiopeiae, it appears brighter, as we can see in both pictures shown in this article.
The Ghosts of Cassiopeia are emission nebulae. Their spectra show H-alpha emission lines, which indicate the presence of hydrogen in the cloud. You can see it in red in this image, mostly in the inner parts of the nebula. The title picture of the Cassiopeiae was taken using a ZWO Kamera ASI 1600 MM-Cool V3 Mono camera, mounted on a Celestron RASA.
The brightest part of this nebula is due to the ultraviolet radiation emanating from the neighbor star, which is reflected by the dust particles. UV light keeps bombarding the gas electrons, giving them more energy which they release later as H-alpha radiation when they recombine with hydrogen atoms. Hence, we see this red color in the nebula. Although Gamma Cassiopeiae is giving the nebula its beautiful colors, it is also slowly dissipating it due to proximity and to the very strong UV emission. But the ghosts are not expected to disappear soon from our sights, as they are part of a much larger nebula surrounding the star. This large nebula measures approximately 2 degrees, which is equivalent to four full Moons. Even if our bare eyes cannot see these friendly ghosts, telescopes can show us the unseen wonders of the sky.