Answer to Question 1
Shapley began his research on the star system by noticing that, although open star clusters are scattered all along the Milky Way, more than half of all globular clusters lie in or near the constellation Sagittarius. The globular clusters seem to be distributed in a great cloud with a center located in the direction of Sagittarius. Shapley assumed that the orbital motion of these clusters is controlled by the gravitation of the entire star system, and for that reason he concluded that the center of the star system must lie somewhere toward Sagittarius.
Answer to Question 2
Zero Age Main Sequence
Structure of the Early Universe
The X-ray crystal structure of an S1 fragment of myosin II
Glycerophospholipid structure
The chemical structure of the water molecule facilitates life
Age structure for the United States
Manhattan plots resulting from a genome-wide association study of seven common human disease