# Essay: The Universe

Abstract
The universe is a known place to our young and sensitive eyes. Stars galaxies, planets, comets, asteroids are part of this abundant place that has an end of 13. 8 billion years to us. The age of the universe was known by studying the oldest objects within the universe, which can be studied using binary system or the HR Diagram. Knowing how fast the universe is expanding can be done by knowing how close and far are objects from us and their velocity towards or away from our galaxy. Finally we can know the observable universe by knowing how light and light speed works and travels in space.

Introduction
What is in the universe?
Galaxies, planets, stars, comets, asteroids, and much other chemical composition ‘stuff’ are part of the universe. We are not able to see the entire universe but just the observable part of it. The observable universe is a term referring to the volume of space that we are physically able to detect, it can be defined as what we are potentially able to see, is there more? That is unknown to our eyes. The universe is 13.8 billion years old to us this is until what our eyes can see. The age of the universe was known because of these main reasons, one, by studying the oldest objects within the universe and second, by measuring how fast the universe is expanding, but the one and most important is knowing how light and light speed works and travels in space.

Main body
Studying the oldest objects within the universe
Many countless objects are part of the universe having each a different birthday, one year, ten years and up to a billion years of age. Studying the age of the objects in the universe has some work attached to it. The life cycle of a star is based on its mass (Redd). We can know that if a star is bright it has a bigger mass causing it to have a longer life cycle. Measuring the mass of a star is easier when using a binary system. Binary system is when two (bi) start orbit around each other. By measuring the orbital speed the orbital period and the size of the orbit we can get to know the mass of both the stars. Another easy method to know the mass of the star and therefore the age of it is using the H-R diagram. Depending where the star is in the H-R diagram we can know the mass and therefore its age. Therefore an example can be, if we want to know the age of star ‘A’ and star ‘B’ we first measure the speed, the orbital period between star ‘A’ and star ‘B’, the size of the orbit and we get to know the mass both. The stellar mass is the mass that we have been using and continue to use in order to know determine the age of a star.
Hertzsprung’Russell diagram
One of the most useful and powerful plots in astrophysics is the Hertzsprung-Russell diagram (hereafter called the H-R diagram). It originated in 1911 when the Danish astronomer, Ejnar Hertzsprung, plotted the absolute magnitude of stars against their colour (hence effective temperature). Independently in 1913 the American astronomer Henry Norris Russell used spectral class against absolute magnitude. Their resultant plots showed that the relationship between temperature and luminosity of a star was not random but instead appeared to fall into distinct groups (Australia). This diagram has several different representation one of which is called the observational Hertzsprung- Russell diagram or color-magnitude diagram (CMD). What this diagram does is that when stars are at the same distance it compares the color, using the color index which can state which star is more luminous. Therefore once we are able to know which star is more luminous we can determine it age.

How fast the universe is expanding
For a fact we know that stars die but there are some stars that live longer than other and by discovering how old is one star and them discovering that another star is older we have come to know that they may not be the limit and by looking more in to it we may find older objects. The universe is expanding every day away from us and towards us. Galaxies and stars are moving and we can know if a star is close to us, away from us or if it is moving closer or farther away from us. Knowing the wavelength range by using infrared light can answer us where are the stars standing now and once we know where the stars are know we can know their color and therefore their age. Farther stars and galaxies are moving way faster from us that does closer stars and galaxies, this is due to the young age they have which allows them to move in a faster rate.

Light
The speed of light is what determines our possible visibility of the universe. The speed of light is defines as C= the speed of light= 300,000km/s or 3.0 * 10^8 m/s. A light year is the distance traveled in one year. If you see a star that is 40 light years away, you are seeing it as it was 40 years ago. Thus the deeper you peek into space, the farther you are seeing back in time. Any event that happened beyond a certain point in the past is unknowable to us if the signal from it hasn’t had time to reach us (Observable universe). We can see up to objects that are 13.8 billion light years away from us because 13.8 billion light years is our visible limit. For that reason the universe that old, and there may be more but it has not yet reached our eyes.
Conclusion
Human beings have a limit of the visibility of the universe. The universe to our yes is enormous with all different stars ‘stuff’ that are part of it. Our eyes and our telescopes can only see back to 13.8 billion years. The light has traveled to us in a speed of 13.8 billion light years, and has not yet seen more. We do not have knowledge of how old or what is beyond what we see, this will be known in several billion years more, if they are to come.

Source: Essay UK - https://www.essay.uk.com/essays/science/essay-the-universe/

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Essay UK, Essay: The Universe. Available from: <https://www.essay.uk.com/essays/science/essay-the-universe/> [21-05-19].