Why do the patterns of the stars in our sky look the same from year to year?

Explanation:

When seen from the Earth, all the stars appear to be pasted on a dome like structure. We call it as Celestial Sphere. Though the stars appear to be at equidistant from Earth, they are not. When joined together we can make/imagine a pattern out of them which we call as constellation/asterism.

Even though the stars move and they move at a very high speed. They appear to be stationary for us as they are very far away from us. So even if they move and change positions the pattern will remain same as the change seen from Earth is negligible.  

.) the observation by semmelweis that more mothers died of childbed fever when their doctors also worked in the morgue