ساينس الصف الثالث الاعدادي – الفصل الدراسي الاول ساينس تالتة اعدادي – ترم اول In This part we will study : The galaxy They are groups of stars that rotate together in cosmic space by the effect of gravity The Milky Way the old (large) stars are located in the center. The recent small stars are located in spiral arms of the galaxy. The sun is a star of millions of stars that rotate around the center of milky way galaxy. The solar system It is the sun and eight planets revolving around it. Measuring the distances through the universe: The distance between stars are very large, so it measured by unite called “light year” A light-year The distances in the universe are so vast so that they are measured by the light-years. The light-year is the distance that light travels in a year. – Since the speed of light equals 300000 km per second, The Big Bang Since about 15000 million years, the universe was very small and very hot. Through the Big Bang, the process of expansion and changing started and it continues to this day. Within minutes of the explosion, the atomic particles merged together producing helium and 5 after about 12000 million years of the Big Bang Earliest life forms began to appear on earth 15000 million years after the Big Bang The universe as it now So, we can define the Big Bang as follows: Big Bang: – it is a massive explosion happened, since 15000 million years, resulted in it all forms of matter, energy and time. Or. – it is the expansion of the universe and merging of atomic particles forming helium and hydrogen gases. لمتابعة مستر احمد الباشا وكل ما يخص الساينس : جروب الفيس بوك http://bit.ly/2Of1mcN صفحة الفيس بوك http://bit.ly/2Gq5xMo بالتوفيق مستر احمد الباشا