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Is it spring? To answer this question, step outside; what evidence of spring do you see, hear, or feel?
Ask an astrophysicist when spring begins and she will likely consult the solar calendar. According to that, spring arrived last week at 1:14 AM EST on Tuesday, March 20, 2012. That moment marked the vernal equinox, the point at which the sun crossed the celestial equator. By this definition, spring cannot be early or late. It is a fixed moment in time.
Ask a meteorologist and she will likely respond that spring was early this year. As evidence, she might cite the record-breaking warm temperatures across the Midwest, East Coast, and Canada.
What makes it spring? It is both a moment in time, and a series of natural events. To understand spring you must understand the Earth’s trip around the sun, phenology, and animal migration. This week, you will explore each. You will examine the synchronous pieces that combine to create spring. You will also investigate why an early spring may not be something to celebrate.
The vernal equinox marks the moment each year at which the earth experiences equal amounts of light and dark, day and night. The vernal equinox is commonly known as the first day of spring. Visit the Adler Planetarium interactive to learn more about the relationship between the sun and earth, and how the earth’s movement creates seasons. (At presstime, there was one error at the beginning of the interactive. Did you catch it? Hint: How many planets are there?) Complete the three activities to test your knowledge of the seasons. Try working without the hemisphere hint.
Once you understand the orbit of the earth and how this affects seasons, try a more difficult exercise. The first page offers a graphic that introduces key terms. Continue to the interactive for an independent exploration of the earth’s orbit. Activate lines on the map to show the equator and the four cities by clicking their boxes in the chart. Use the arrows to change the month and see how the position of earth alters. Choose one city to track. Click through each month, pausing to examine what is altered and how. How does the temperature change as the year progresses?
How does the amount of daylight change? What month is warmest? What month has the longest amount of daylight? How is this city different than the other cities? When does spring arrive in each of the four cities?
Technically speaking, the beginning of spring is a specific date and time set by the solar calendar. However, the signs of spring vary from year to year. Phenology is “the study of recurring biological phenomena and their relationship to weather.” Examples of this are the first leaf on a tree or flower bloom, and seasonal animal migration. Phenologists track these annual events and use them as indicators of spring’s arrival. Watch this video from Wisconsin Public Television to learn more about phenology.
The pattern of these springtime firsts indicates spring is becoming earlier. View a state-by-state map that illustrates how early spring has arrived. What do the colored box and grey box on each state’s calendar represent? How is spring’s arrival being measured? How has springtime changed in your state? In what regions of the United States has spring’s arrival changed most drastically? In what region has spring’s arrival changed the least?
One other common indicator of spring is the seasonal migration endured by some species of animal, fish, insects, and birds. For an introduction to animal migration, view this episode of D4K, hosted by Idaho Public Television. Watch the first 8:47. Then, read the facts of animal migration. What are three reasons animals migrate? How does the solar calendar effect animal migration? What role do the sun and stars play in some migrations? Would an early spring affect those signals? How?
For a closer look at four different species’ migrations, view the first chapter of Earth Navigators from the PBS series, Nature. This show follows the migrations of Hooper swans, wildebeest, Monarch butterfly, and salmon. As you view, consider: For what reason does each species migrate? What type of migration is each? What cues tell each species that it is time to migrate? How would these migrations be affected by earlier spring temperatures? What do you find most amazing about these migrations? What questions do you have?
What’s not to Like?
Why are earlier springs important? Why not just take a book outside and enjoy a beautiful, if early, spring day? What do you predict are some side-effects of an early spring? How are plants, animals, and migration affected? How do seasonal activities rely on each other? How is one event affected by changes to another?
Heidi Cullen, a climatologist, shares her thoughts on early springs in her op-ed, Spring Gets Ahead of Itself. Be sure to read the full version. (The link to it is at the bottom of the page.) Summarize Cullen’s main points. What questions or responses does her piece provoke?
For a deeper view of how early springs will affect animals, especially their migrations, read the National Wildlife Federation article, Perilous Journeys. How are migratory animals affected by global warming? How do human activities affect animal migration? How have some species adapted to these changes? What do scientists and nature enthusiasts fear will happen if animals are unable to adapt?