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
Palade's use of the pulse-chase method to study protein secretion
Evolutionary changes in flower structure
Structure of HIV
The basic structure of an antibody molecule. Two heavy chains are joined by two light chains. The ...
The elements of chromatin structure
Structure of the lac repressor