Based on astronomical principles and facts it is possible to conduct a study of the stars and galaxies. In so doing we can use segments of the electromagnetic spectrum to understand the diverse nature of these features. The electromagnetic spectrum is the range of frequencies possible in the electromagnetic radiations. Under it therefore we look at the visible light/radiation, the x-rays, ultra violet radiation, infrared radiation, radio waves and gamma rays among others. In the present world it is notable that the most contents or objects in the universe have substantially lost light becoming dimmer an example being the stars and galaxies. This shift in light may perhaps be as a result of the expansion of the cosmos in that as the universe undergoes expansion most galaxies get more and more separated. However this can be established by analyzing the visible light/radiation and the gamma rays radiation which is the most energetic of photons.The importance of this is that by studying the various galaxies and making an observation in its diversity and place of strength in terms of position in the electromagnetic spectrum a lot can be deduced.A galaxy is a system of stars and gas which exist in variety of sizes and shapes. Stars on the other hand can be defined as a large celestial body which is normally composed of gravitational hot gases that emit electromagnetic radiations as a result of nuclear reactions within them. They are said to be in rapid motion but then their change in position is notable over centuries. There are various types of galaxies including the elliptical, spiral and irregular. This implies that there are large and dwarf galaxies with the dwarf being most common and the large ones being a result of merger of small ones. The merger of different gas clouds is responsible for the different galaxy types (Miller 50).In understanding the variance in light of the galaxies, it is important to note that most galaxies contain central black holes which attract matter into the forming galaxies. However such action forms quasars which with time have grown as distant in that as the black holes acquired more matter from the canters of the galaxies their fuel reduced and so quieting them down. The situation can only be salvaged by interaction of galaxies. The more massive the central burge of a galaxy the more Massive its black hole and hence the nature of an active galaxy nucleus which explains the visible light of the galaxy (Chaisson 20).
From most galaxies it is notable from reports in 2010 that the gamma rays detected were gigantic and produced a flare that lasted 20 days and the degree and direction of the visible light polarization had also noted a great shift. The gamma rays and the visible light emitted always have a great connection with each other.The Other notable galaxy is the Seyfert galaxy which is a spiral galaxy and whose nucleus is bright and compact. Its outer part is not clearly seen but it has a bright nucleus which resembles a star, therefore the nucleus of the seyert looks like a quasar. The Seyfert do not emit strong radio waves but then the nucleus normally radiates so strongly over a wide range with its gamma ray emission notably at I million ev and the intensity of its peaks seen to be at 450 NM emission line. In this case therefore we realize that they are thus less luminous compared to the quasars but then brighter than normal spirals like for instance the milky way. However it is becoming increasingly notable that the brightness of these Seyferts undergoes lots of changes over short periods of time like within days due to the fact that they have black holes at their nucleus in which matter falls.
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There are also galaxies that are referred to as radio galaxies which are so called because they are sources of radio emissions which are known to radiate strongly at radio wavelengths unlike other galaxies. From these radio galaxies the visible light is so strong in that they are said to be more luminous being thousands of times stronger than the Milky Way. These strong radio emissions are notably associated with the elliptical galaxies. This is perhaps a result of the radio jet which can be attributed to the gamma rays emissions which results from the core of the active galaxy nucleus (Clay 37).The other most notable galaxy is the Milky Way galaxy, it is ordinarily spiral. We note that the spiral galaxy called the Milky Way lies 50 million light years towards the Pegasus constellation. It is made up of several young stars. It does not exist in isolation and it is notable that it is formed from merging of smaller stars. The evidence of its formation can be seen in the tearing of satellite galaxies and incorporation of their stars the Milky Way also has the black hole at its centre and this is more evidence to the issue of dwindling visible light and gamma rays emission. It is said that with time the black hole gets to close that is after reaching a particular mass this thus shuts off its growth. This perhaps brings out the fact that most galaxies had a youthful bright quasar like phase but the n dwindles with time. The gamma ray sky also has maintained a constant shift (Sparrow 25).From observations made on the visible light and the gamma rays emission of most of the galaxies it is notable that the elliptical galaxies seem to be continuously expanding in their sizes over time. The mass however is remaining constant but then we realize that with time the galaxies will disappear due to evaporation of matter and that small and brighter objects are getting replaced with large but dimmer objects. This explains the darker nights with the time. The two segments of the electromagnetic spectrum thus shows and explain the dimming of stars and galaxies and the effect it has at large in our cosmos.