Solar Physics Essay -- solar physics

The star we call the Sun has a number of small objects circling around it. Many other stars in our Galaxy have objects orbiting them too and astronomers have recently discovered a few of these other systems already. The largest members of the Sun's family are called planets, and one of these we call home. That planet, Earth, has many unique characteristics that enable life to exist on it. What are the other planets like? We have learned more about our solar system in the past few decades than probably any other field of astronomy. The planets are no longer just objects up in our sky, but places we have been and explored---worlds in their own right. To give an adequate coverage of each of the planets would fill up a whole book (or more)! Since this web site is an introduction to all of astronomy, I will not explore each planet individually. Instead, I will focus on the common characteristics of the planets such as their Distance relative to us, mass, size and etc. Distances Several hundred years ago Copernicus was able to determine approximate distances between the planets through trigonometry. The distances were all found relative to the distance between the Earth and the Sun, the astronomical unit. Kepler refined these measurements to take into account the elliptical orbits. However, they did not know how large an astronomical unit was. To establish an absolute distance scale, the actual distance to one of the planets had to be measured. Distances to Venus and Mars were measured from the parallax effect by observers at different parts of the Earth when the planets were closest to the Earth. Knowing how far apart the observers were from each other and coordinating the observation times, astronomers could determine the ... ... ? Angular velocity = 36 degrees / 4 hours = 9 degree/hour Full time rotation = 360 degrees / 9 degree/hour = 40 hours With the invention of radar, the distance to Venus could be determined very precisely. By timing how long it takes the radar beam travelling at the speed of light to travel the distance to an object and back, the distance to the object can be found from distance = (speed of light) Ãâ€" (total time)/2. The total time is halved to get just the distance from the Earth to the object. Using trigonometry, astronomers now know that the astronomical unit =149,597,892 kilometers. This incredible degree of accuracy is possible because the speed of light is known very precisely and very accurate clocks are used. You cannot use radar to determine the distance to the Sun directly because the Sun has no solid surface to reflect the radar efficiently.