Our earth, space Celestial body, like the galaxy, sun, star, planet, comet, etc. present in a system collectively called universe or cosmos. And the study of these is called cosmology.
Our universe is made from billions of galaxies, and every galaxy has billions of stars. These stars may have their own family like the solar system, which has eight planets, including earth as a member of the family.
It is believed that the universe originated around 15 billion years ago in the form of a dense, hot blob of gas expanding rapidly towards outward. At that time, the universe contained only hydrogen (H) and a small amount of helium(He). At that time, no stars and planets existed. The first stars began to form out of hydrogen when the universe was some 100 million years ago. This is the process of origin of the Sun, about 4.49 billion years ago.
Big Bang Theory
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Scientist Georges Lemaitre (1927) proposed a model for the origin of the universe, which was known as Big Bang theory. This Big Bang theory explains the origin of the universe, with the key idea that the universe is expanding. Previously, the universe was very denser and hotter—all space contained in a single point, which is considered the inception of the universe. Initially, during expansion, the universe freezes, which allowed the creation of subatomic particles, which consist of protons (p), neutrons(n), and electrons(e).
The majority of atoms formed were hydrogen (H), along with helium and traces of lithium. Huge clouds of these elements later fused through gravity to form stars and galaxies. The massive elements were synthesized within stars. Hence, the Big Bang theory doesn’t explain the initial condition of the universe, but instead, it describes the general evolution of the universe.
Einstein's Theory based on relativity. Which also considers the homogeneity and isotropy of space. It was the scientist Edwin Hubble, who discovered that the distances to remote galaxies were correlated with their redshifts. Also, according to Hubble, all the observable areas of the universe are receding from each other.
In the year 1992, the launching of the Cosmic Background Explorer satellite showed that 99.7% of the energy in the universe was released during the first year of its evolution. This confirmed that the Big Bang theory, which proposes that the universe originated from a single explosion of a very minute amount of matter of high density and temperature.
REDSHIFT
It is measured by examining the absorption or emission of lines in its spectrum. These lines are unique for each and every element and always have the same spacing. When an object in space moves towards or away from us, the spectral lines can be found at different wavelengths relative to the place where the object is not moving.
Now, three types of redshift occur in the universe
(a) From the universe's expansion,
(b) From the movement of the galaxy relative to each other
(c) From "gravitational redshift," which happens when the light is shifted due to a large amount of matter present inside of a galaxy.
Redshift helps astronomers to compare the distances of faraway objects. In 2011, scientists had seen the farthest object — a gamma-ray burst called GRB 090429B.
It is also used to measure how the universe is structured on a large scale.
BLUE SHIFT
Blueshift is used to describe an object moving toward another object or toward blue-shifted say "That galaxy is blue-shifted with respect to the Milky Way," which means that the galaxy is moving toward us in space. It also explains the speed which galaxy is taking as it gets closer to us.
Blueshift is also a direct result of a property of an object's motion called the Doppler effect, though there are other processes which can also result in light to become blue shifted. Here's how it works. Let's take that galaxy as an example again. It is emitting radiation in the form of light, x-rays, ultraviolet, infrared, radio, visible light. As it approaches towards an observer in our galaxy, each photon that it emits appears to be produced closer in time to the previous photon. This is possible due to the Doppler effect and the galaxy's proper motion. The result is that the photon peaks appear to be closer together than they are, making the wavelength of light shorter, as determined by the observer.
Blueshift cannot be seen with an eye. It describes how light is affected by an object's motion. Blueshift can be determined by measuring tiny shifts in the wavelengths of light from the object. It is done by an instrument that splits the light into its component wavelengths. Instruments which are used for this purpose are spectrometer or spectrograph. The data they obtain is graphed into the spectrum. When the light information tells us that the object is moving toward us, the graph will be shifted towards the blue end of the electromagnetic spectrum.
With the help of measuring the spectral shift of stars in the Milky Way, astronomers can get not just their movements, but also the movement of the galaxy as a whole. Objects which are moving away from us will redshifted, whereas, objects approaching towards us will be blueshifted.
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