Once, mankind believed that the Earth is the center of the solar system, and the entire universe as well. Though tempting as it seems, this narcissistic view was perceived due to the observable motions of the visible heavenly bodies in the sky. However, as mankind learns to invent more powerful tools to understand the cosmos, they learn not just the fact that the sun is the center of the solar system, but also the place of the Earth in the universe. In fact, the view of our place in the universe gradually changed as science and technology cemented over time. Today, scientists are able to locate our place in the universe, as well as measure the visible universe (Krishner, 2005). To understand where the Earth lies in the cosmos, this discussion will move outwards, beginning with the place of the Earth in the solar system, until the visible universe.
The Earth is one of the rocky planets, which means that it belongs to the group of planets closer to the sun. To be specific, the Earth lies as the third planet situated between Venus and Mars. The Earth, as well as the other planets in the solar system, revolves around the Sun. The Sun, on the other hand, belongs to a galaxy called the Milky Way Galaxy. The Milky Way Galaxy is a spiral galaxy consisting of several major and minor spiral arms. Our Sun is located in the Orion Arm, one of the outer spiral arms of the Milky Way Galaxy. Orion Arm is a 3000-parsec spiral arm, where the Sun is situated approximately 28,000 light-years away from the center of the Milky Way Galaxy (Robin et al., 2003).
The Milky Way Galaxy has a length of about 30,000 parsecs. Its nearest neighbor galaxy is the Andromeda Galaxy, about a little over 2 million light-years away (Eisenhauer et al., 2003). Like social groups, the Milky Way Galaxy belongs to a small cluster of neighboring galaxies and bodies. The small group called the Local Group includes our Milky Way, the Large and Small Magellanic Clouds, the Andromeda Galaxy, M33 and other neighbor galaxies. Modern day measurements allow astronomers to determine other details, such as the distances and dimensions of galaxies within the Local Group (Powell, 2006). Various other neighboring galaxies also belong to clusters, such as the Local Group. The Local Group has a length of about 3 million parsecs (Mateo, 2006). The nearest cluster to the Local Group is the Virgo Cluster, about 50 million light-years away (Krishner, 2005).
It is also important to note that the Local Group moves with a velocity similar to other neighboring galaxies. To be specific, these galaxies move towards the Virgo Cluster and away from the Local Void; hence, this group of galaxies is named the Local Sheet. Moreover, like galaxies forming clusters, clusters also form a larger cluster. The Local Group belongs to the Virgo Supercluster, a supercluster comprising of galaxy groups and clusters centered on the Virgo Cluster. The Virgo Supercluster has a length of about 30 million parsecs, where the Local Group is situated near the outer edge. Similarly, the Virgo Supercluster belongs to the Laniakea (Choi, 2014), a group of superclusters covering about 160 Million parsecs (Gibney, 2014). Finally, the Observable Universe covers the entire observed galaxies, clusters, groups, filaments and voids.
The length of the Observable Universe is roughly 28 billion parsecs. Note that the center of the Observable Universe is the Earth, due to the limits of observations. The entire data related to the universe are measurements performed on Earth, or near Earth (i.e. man-made satellites and space telescopes), which explains why the Observable Universe is centered on Earth. These measurements include the determination of distances and lengths as suggested by the emissions of infrared, radio, gamma waves and other radiations. There are other techniques to determine these quantities. With the help of powerful telescopes and radio telescopes, astronomers are able to map the Observable Universe (Tully, 1982).
It is also notable that what lies beyond the Observable Universe is unexamined regions due to the fact that the light from these regions has not reached the Earth yet. Needless to say, there is no available information about what lies beyond the Observable Universe.
References
Choi, Charles Q. (3 September 2014). “New Galactic Supercluster Map Shows Milky Way's 'Heavenly' Home.” Space.com. 4 March 2016. Retrieved from http://www.space.com/27016-galaxy-supercluster-laniakea-milky-way-home.html
Eisenhauer, F. et al. (2003). A Geometric Determination of the Distance to the Galactic Center. The Astronomical Journal, 597(2): L121-L124.
Gibney, Elizabeth. (3 September 2014). “Earth's new address: 'Solar System, Milky Way,Laniakea'.” Nature. 4 March 2016. Retrieved from http://www.nature.com/news/earthsnewaddresssolarsystemmilkywaylaniakea1.15819
Krishner, Robert P. (2005). The Extravagant Universe: Exploding Stars, Dark Energy, and the Accelerating Cosmos. 4th Edition. Princeton, NJ: Princeton University Press.
Mateo, Mario L. (2006). Local Group. In Paul Murdin (Ed.), ENCYCLOPEDIA OF ASTRONOMY & ASTROPHYSICS. Hoboken, NJ: Nature Publishing (np).
Powell, Richard. (2006). [Graphic Map of the Virgo Supercluster]. An Atlas of the Universe. Retrieved from http://www.atlasoftheuniverse.com/virgo.html
Robin, A. C. et al. (2003). A Synthetic View on Structure and Evolution of the Milky Way. Astronomy & Astrophysics, 409: 523-540.
Tully, R. Brent. (1982). The Local Supercluster. The Astrophysical Journal, 257: 389-422.
