Earth Science
How do we calculate or determine the distances to stars?
The distance between the stars and the earth is much hence calculating the distance between the two objects might actually become a problem. To be capable of solving the problem of distance between the earth and the stars, the astronomers use parallax method to approximate the distance. The distance obtained is not accurate since the method only approximate the distance between the two body masses. To be capable of achieving an accurate measure, the astronomers would have to travel from the earth to the stars. This might be a difficult task since the stars are far way and millions of kilometers away from the earth’s surface (Inglis, 2003).
Since the earth revolutions around the sun, all the stars in a manner appear to shift location in opposition to the farther stars. In this case, the scientists use a method referred to as the parallax shift, which enables the astronomers in achieving the distance of the star from the varying position of the earth. By being in a position of identifying the distance of shift, the astronomers relate the distance to the diameter of the orbit of the earth. This accurate distance and diameter is vital in obtaining the calculation of the parallax angle, which is assumed to be across the sky. The parallax shift is the essential determiner of how far the star is away from the earth. The smaller the parallax shift is achieved; this indicates that the stars are far away from the earth (Seeds & Backman, 2011).
However, when the parallax shift is large and bigger in distance, it denotes that the stars are close to the earth’s surface. For this reason, it is true to state that the distance of the stars from the stars from the earth can only be approximated. The level of accuracy is in relation to the distance, size and the motion of the earth in relation to the position of the stars. Distance is arguably the hardest measurement in the field of astronomy though those in the field have been able to come up with methods that can estimate it. The measurement for distance of the stars that are beyond 100 light years is through use of Cephid capricious stars whose brightness keeps on changing therefore allowing astronomers to estimate their true brightness. With comparisons of the visible brightness and the real one, astronomers can determine the distance. However, there are methods for approximating the distance for those that are not beyond 100 light years (Shipman, Wilson & Higgins, 2013). One of the methods is the Astronomer’s Triangulation method that starts with utilization of a lengthy baseline that determines the orbit of the Earth’s diameter.
What units do we use?
Astronomers go on to determine the parallax while the surveyors then measure angles at the end of the baselines with both measurements culminating to one conclusion- the shape and size of the triangle and therefore determining the distance to the object. The special units for measurement of this distance are called the parsec (pc) which can be defined as distance to an imaginary star with a 1 arc second parallax. One parsec is 2.06*10^5 or simply 3.26 ly, which makes it easy to calculate the distance by using d=1/p with the parallax being expressed in arc seconds whereas for distance, parses will be used (Inglis, 2003).
What are the limitations? (if any) of the methods
However, this method has a big limitation on its part; it is very hard to measure parallax due to the small angles involved. I context, Centauri which is the star nearest to the sun, has a parallax of only 0.742 arc seconds (Woolfson, 2011). The larger the distance is, the lesser the parallax becomes. The blurring that is brought about by the atmosphere smears images of the stars and makes their diameter to be approximately 1 arc second, which increases the difficulty in measurement of parallax. Although, the use of many averages of their observations, the astronomers are unable to estimate the parallax from earth without an uncertainty larger than 0.002 arc seconds. For this reason, the method is limited in giving the accurate figures (Shipman, Wilson & Higgins, 2013).
References
Inglis, M. (2003). Observer’s guide to stellar evolution: The birth, life and death of stars. London [u.a.: Springer.
Seeds, M. A., & Backman, D. E. (2011). Stars and galaxies. Boston, MA: Brooks/Cole, Cengage Learning.
Shipman, J. T., Wilson, J. D., & Higgins, C. A. (2013). An Introduction to Physical Science. Boston, MA: Brooks/Cole, Cengage Learning.
Woolfson, M. M. (2011). On the origin of planets: By means of natural simple processes. London: Imperial College Press.
