Directions: Complete the following sentences with the correct word or words.

1.             1.   The two factors that combine to keep Earth and the moon in their orbits are _________________ and _______________________.
2.             2.   The tendency of a moving object to continue moving in a straight line or a stationary object to remain in place is called ______________________.
3.             3.   The _______________________ system gained support when Galileo observed that Venus goes through phases similar to those of Earth’s moon.
4.             4.   The sun produces energy by______________________________.
5.             5.   The ______________________ is the layer of the sun you see when you look at an photograph of the sun.
6.             6.   The _____________________ is a stream of electrically charged particles that extend outward from the sun’s corona
7.             7.   In a ______________________ system, Earth revolves around the sun
8.             8.   All inner planets are small and have __________________ surfaces.
9.             9.   Aside from Earth, it is believed that _______________ is the only other planet that once had liquid water on its surface.    
10.           10.   The atmospheres of the __________________________ planets cannot escape into space because the planets have very strong gravitational pulls.
11.           11.   The first four outer planets are much larger than ____________________ and are made mainly of hydrogen and helium.
12.           12.   The fact that each planet’s orbit is an ellipse was discovered by __________________.
13.           13.   The asteroid belt is located between ________________ and ____________________.
14.           14.   When a meteoroid enters Earth’s atmosphere, it produces a streak of light called a(n) _________________.
15.         
16.           15.   The orbits of most comets are long, narrow _________________________.
17.           16.   One of the conditions required for life on Earth is ________________ water.
18.           17.   ______________________ is considered a good place to look for life because there may be liquid water under its icy crust.
19.           18.   _____________________ is the scientist who explained that the sun is at the center of the system of planets.
20.           19.   The sun’s __________________ can only become visible during a solar eclipse.
21.           20.   _________________ and Earth are much alike in terms of their size and density.
22.           21.   Saturn’s rings are made up mostly of chunks of ____________ and rock.
23.           22.   ________________ is different from most other planets because it rotates on its side.
24.           23.   _______________________ is the largest and most massive planet.
25.           24.   _______________________ is very similar in size and color to Uranus.
26.           25.   _______________________ is the smallest terrestrial planet.
27.           26.   Earth is thought to be at the center of the solar system in the ____________________ model.
28.           27.   All of the ____________________________ planets have many moons.
29.           28.   The _________________________ planets are small, dense, and have rocky surfaces.
30.           29.   The Great Red Spot is a huge storm on____________________.
31.           30.   A comet or asteroid can break up to form a chunk of rock called a _________________.
32.           31.   Sunspots are darker than the rest of the sun because they are made of gas that is ____________________ in temperature.
33.           32.   A ______________________ is a loop of gas on the sun’s surface.
34.           33.   The sun’s _________________ is the layer of the sun’s atmosphere that looks like a white halo.