The above link explains what a light year is. Great site for everyone. I have tutored some earth science, not my forte.
“California Education Code Section 51225.3 (a)(1)(C) specifies, in order to receive a high school diploma, a student must successfully complete at least two courses in science, including biological and physical sciences.
“A course is one year long or two semesters. While the law is not explicit, one course generally focuses on the biological sciences and the other course focuses on physical sciences. Physical sciences may include physics, chemistry, or earth science. Two years of integrated science would also fulfill this graduation requirement, as long as biological and physical sciences are included.”