Name: Date: LAB: What Events Mark the Beginning of Each Season? The relationship between the Sun and Earth have been used since antiquity to measure time. The day is measured by the passage of the Sun twice in succession across the meridian of the observer. Each day is divided into two main periods. The 12 hours before the Sun reaches the meridian are called ante meridiem (A.M.), meaning before noon. The 12 hours after the Sun passes the meridian are called post meridiem (P.M.), meaning after noon. The year is measure by the time it takes for the Earth to make one trip around the Sun. On Earth, the year spans the time it takes for the vertical ray of the Sun to move from the Tropic of Cancer to the Tropic of Capricorn and back to the Tropic of Cancer. The year is divided into four seasons. During each season, the vertical ray moves 23 ½º of latitude. In this investigation, you will analyze the migration of the Sun s vertical ray and other events that mark the first day of each season. Materials: globe, light source, sun-earth planetarium Procedure: 1. Figure 1 is a diagram of the Earth in Space. Label the axis and all the parallels in this figure. Use your notes and Reference Tables if needed.
2. Figure 2 shows the positions of the Earth on its orbit around the Sun on each of the first days of the seasons. At each position, label the name of the day, the approximate date, and the parallel where the vertical ray strikes at noon that day. 23 1 / 2 Name: Date: Vertical Ray: SUN Name: Date: Vertical Ray: Name: Date: Vertical Ray: Name: Date: Vertical Ray: 3. On the planetarium and using the model Earth and Sun, study the relationship between the Earth and Sun on each of the seasonal days by revolving the Earth around the Sun (or by simple orienting the North Pole of the Earth in relation to the Sun) and observing where on Earth a vertical ray of light from the Sun strikes. Note the direction that sunrise and sunset occurs for an observer on Earth. Also note where the Sun would be in the sky and the duration of daylight for an observer at various latitudes on Earth. 4. Summarize your findings in the table on the next page. You will find figures 1 and 2 helpful. Keep in mind that the altitude of the noon Sun changes 23 1 / 2 each season. For example, if the noon Sun were at 60º on the vernal equinox, it would be at 83 1 / 2 on the summer solstice when the sun reaches its highest point for the year (60º + 23 1 / 2 = 83 1 / 2 ). On the winter solstice, this angle would equal 60º - 23 1 / 2, or 36 1 / 2.
Event Date Summer Solstice Autumnal Equinox Winter Solstice Vernal Equinox Tilt of Axis (relative to Sun) Latitude of Vertical Ray Length of Day (hours of daylight) Equator North Pole South Pole Boonville Sunrise and Sunset Altitude of Noon Sun (degrees) Equator Boonville Equator Tropic of Cancer Tropic of Capricorn Boonville What Does Your Investigation Reveal? 1. Describe the three basic causes of the seasons: 2. Why is the location of the Sun s vertical ray a determining factor in seasons? 3. At what rate (in degrees) does the vertical ray migrate each season? each year? each day?
4. Using the information from the previous question, if the Sun is at a latitude of 23 1 / 2 South on the Winter Solstice, where is the vertical ray located today? Show your calculations here: 5. How do seasonal changes affect weather and climate in the mid latitudes? 6. Describe the effects of the changing seasons in the equatorial latitudes. 7. What are the seasonal patterns of weather and climate in the polar regions? 8. If the Earth s axis were inclined at 35º from vertical, how would the range of temperatures in the middle latitudes be influenced?
Analyzing Celestial Observations Use the information from the lab activity to answer the following questions. For each question, state the relationship that exists between the following sets of variables at the start of each season (summer solstice, winter solstice, equinoxes). Answer the following for a location in Boonville: 1. Time of Year and Solar Altitude at Mid-day 2. Time of Year and Points of Sunrise and Sunset 3. Time of Year and Hours of Sunlight 4. Solar Altitude at Mid-day and Point of Sunrise and Sunset 5. Hours of Sunlight and Points of Sunrise and Sunset
6. Solar Altitude at Mid-day and Hours of Sunlight For Further Thought 1. Is there ever a time when the noon Sun is north of an observer in Boonville? 2. An observer in Boonville notices that she is casting a shadow that extends from her feet toward the southeast. What time of year must it be? What time of day must it be? Use the celestial sphere model to help you. 3. Is there ever a time when the Sun appears to rise exactly east and set exactly west for an observer in Boonville? If so when? BONUS: The altitude of the mid-day Sun for an observer in Boonville on November 22 is 29º. Where on Earth must a person be standing at that exact moment for the altitude of the Sun to be 90º? (Assume the latitude of Boonville is 43º) Show your work in the space below.
Reading Comprehension Read the portion of the article on Seasons below and answer the following questions based on the reading. Use complete sentences. Earth's tilt creates seasons By Jack Williams, USATODAY.com 12/20/2005 http://www.usatoday.com/weather/tg/wseason/wseason.htm The reason for changes in Earth's seasons is the Earth's tilt, not its distance from the sun. In the Northern Hemisphere summer, the land north of the equator is tilted towards the sun, allowing more of the sun s energy to heat the Northern Hemisphere. Conversely, during the Northern Hemisphere winter, the land north of the equator is tilted away from the sun, which lowers the amount of the sun s energy warming the Northern Hemisphere. The Earth is actually closer to the sun during the Northern Hemisphere winter, but since the hemisphere is tilted away from the sun, it still feels like winter. In fact, the Earth's average temperature is actually higher in July, when it's the farthest from the sun. "Averaged over the globe, sunlight falling on Earth in July (aphelion) is indeed about 7% less intense than it is in January (perihelion)," says Roy Spencer of the Global Hydrology and Climate Center in Huntsville, Alabama. Still, "the average temperature of Earth at aphelion is about 4 degrees F (2.3 degrees C) higher than it is at perihelion." Why is the Earth warmer when we're farther from the sun? It's because there's more land in the Northern Hemisphere and more water in the south. During July the land-crowded northern half of our planet is tilted toward the sun. Land warms faster than the water. "Earth's temperature (averaged over the entire globe) is slightly higher in July because the sun is shining down on all that land, which heats up rather easily," says Spencer. 1. What is the reason for the seasons? 2. How much less intense is the Sun in July due to its distance? 3. Why does the amount of land affect temperatures