2. Earth-based and space-based astronomy reveal the structure, scale, and

changes in stars, galaxies, and the universe over time. As a basis for

understanding this concept:

a. Students know the solar system is located in an outer edge of the disc-shaped

Milky Way galaxy, which spans 100,000 light years.

b. Students know galaxies are made of billions of stars and comprise most of

the visible mass of the universe.

c. Students know the evidence indicating that all elements with an atomic

number greater than that of lithium have been formed by nuclear fusion in

stars.

d. Students know that stars differ in their life cycles and that visual, radio, and

X-ray telescopes may be used to collect data that reveal those differences.