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
Platelet structure.
Structure of the water molecule
The Structure of an Old High-Mass Star
Structure of the human immunodeficiency virus (HIV).
Structure of the nucleosome core particle as revealed by X-ray diffraction
Structure of Al2Cl6