I have just started the space unit in school and have 3 questions. I hope someone can answer and explain. I would appreciate!![]()
1) "If you look into the night sky, you will see a cloudlike band of stars that stretches across the sky. Because of its milky appearance, this part of the sky is called the "Milky Way". The "Milky Way" is the disk of the "Milky Way Galaxy".
I don't get this part! Are "Milky Way" and "Milky Way Galaxy" the same thing or are they different? What is a "disk" and what does it mean by "The 'Milky Way' is the disk of the 'Milky Way Galaxy'."?
For example, in the following picture, which part is the disk?
2) As you observe the night sky, why do stars apear to move westward across the sky?
I would say earth's rotation causes stars to appear moving westward around a central point (Polaris). And earth's revolution causes them to shift slightly to the west each night, over a period of a year. Am I right?
3) "The earth is 4.6 billion years old. How many revolutions around the center of galaxy has it travelled? The sun is located in one of the spiral arms and completes one revolution in about 200 million years."
For the sun, I can calculate that it has completed 460000000/200000000=23 revolutions around the center of the galaxy? When the sun completes one revolution around the center of the galaxy, does the earth completes one revolution around this center, too?