1.  As a comet gets closer to the sun, the size of its tail _______________________.

3.  Impact Craters form from meteoroid fragments. The diameter of the crater depends on the size and speed of the meteoroid.

4.  Much evidence of craters is missing due to erosion, which DOESN’T destroy the crater evidence on the moon.

5.  The dinosaurs became extinct around 65 million years ago.  In fact, 65% of all species on Earth became extinct at that time.

6.  The theory is that an asteroid or comet hit Earth, forcing dust into the atmosphere and blocking the sun for years

7.  This may have changed the climate causing plants to not grow and resulting in the starvation of these species.

8.  After the Big Bang, clouds of hydrogen and helium began forming, which were the beginnings of galaxies.

10.  Galaxies are made of billions of stars and are about 10 billion years old.

11.  Some galaxies, such as the Milky Way are spiral galaxies, resembling pinwheels with huge spiral arms. This galaxy is disk shaped and rotates counter clockwise, taking about 230 million years for one revolution.

13.  Stars begin as nebula (huge masses of dust and gas (hydrogen)) that condense in space.

14.  As stars are compressed by gravity the temperature rises and nuclear fusion begins. Nuclear fusion occurs when hydrogen changes into helium, releasing energy, some as starlight

15.  If these stars explode, they become supernova.

16.  If these stars collapse inward, they become black holes.

17.  Star Life Cycle Star Life Cycle

18.  An average star, it rotates on an axis and is about 5 billion years old. It also will be around for another 5 billion years.  Main sequence star- 90% of all stars included in this group

19.  Sunspots are dark spots on the Sun’s surface that represent cooler gases.

20.  These sunspots cycle, hitting a maximum every 11 years and may affect Earth’s climate when less energy is reaching our planet.