Building Vocabulary Match each term with its definition by writing the letter of the correct definition in
the right column on the line beside the term in the left column.
E 4. big bang
a force that is causing the expansion of
the universe to accelerate
5. cosmic background radiation
6. dark energy
b. the asteroid-like bodies that formed the
building blocks of planets
7. planetesimal
c. leftover thermal energy from the big
8. dark matter
bang
9. solar nebula
d. matter that does not give off electro-
magnetic radiation
a large cloud of gas and dust, such as
the one that formed our solar system
a theory that the universe formed in a
huge explosion
e.