1. 17.1 Atmosphere Characteristics

2. Ozone A molecule of oxygen containing three oxygen atoms.

3. Troposphere The lowermost layer of the atmosphere; It is generally characterized by a decrease in temperature with height.

4. Stratosphere The layer of the atmosphere immediately above the troposphere, characterized by increasing temperatures with height, due to the concentration of ozone.

5. Mesosphere The layer of the atmosphere immediately above the stratosphere and characterized by decreasing temperatures with height.

6. Thermosphere The region of the atmosphere immediately above the mesosphere and characterized by increasing temperatures due to absorption of very short wave solar energy by oxygen.

7. Summer Solstice The solstice that occurs on June 21 or 22 in the Northern Hemisphere and on December 21 or 22 in the Southern Hemisphere.

8. Winter Solstice The solstice that occurs on December 21 or 22 in the Northern Hemisphere and on June 21 or 22 in the Southern Hemisphere.

9. Autumnal Equinox The equinox that occurs on September 22 or 23 in the Northern Hemisphere and on March 21 or 22 in the Southern Hemisphere.

10. Spring Equinox The equinox that occurs on March 21 or 22 in the Northern Hemisphere.

11. Key Concept How does weather differ from climate? Weather is constantly changing, and it refers to the state of the atmosphere at any given time and place. Climate, however, is based on observations of weather that have been collected over many years. Climate helps describe a place or region.

12. Key Concept Why do seasonal changes occur? Seasonal changes occur because Earth’s position relative to the sun continually changes as it travels along its orbit.