(Though published online, this Activity follows the format used in the printed Teacher's Guides for this and other PTK Modules.)

Here are some links to pictures of real implementations of the "Horizon Calendar Activity!"  

Central High School, Muncie, Indiana
Gates Intermediate School, Scituate, MA
Willard Middle School

Teacher Background:

For thousands of years, cultures across our planet have used the position where the Sun rises above or sets below the horizon as an indicator of the right time to plant or harvest, to engage in religious observances, or to hit the trail for seasonal migrations. In this Activity, students will observe and record where on their local horizon, the Sun sets over an extended period of time (although any one observation will take very little time). Their record becomes a kind of "horizon calendar" and serves as direct evidence of the underlying reason for the seasons--the changing relationship of Sun and Earth caused by the tilt of the Earth's axis in relation to its annual orbit around the Sun.

Objectives:

Students will observe and record the position of the setting Sun on their local horizon once a week, over a period of several months. Students will present explanations for the observed movement of the Sun, and will revise these based on research including LIVE FROM THE SUN materials and animation available at the LFSUN website and in the video programs.

Materials:

marker for each observation, such as small colored dot

Vocabulary:

equinox, solstice, axis, tilt

Engage:

Ask students to explain day and night (Earth's rotation on its polar axis) and the reason for the changing seasons (Earth's tilt from the plane of its orbit around the Sun.) Explain that even graduates from the nation's most prestigious universities are often unable to provide accurate explanations (see Expand below). One common misconception is that it's colder in the winter because the Earth is then farther from the Sun. Ironically, because of the slight eccentricity of its orbit (which is not a perfect circle around our local star), Earth is actually closer to the Sun during winter in the northern hemisphere.

Ask students whether the sun always rises and sets at the same location on the horizon. In which direction does the Sun set? (A pre-test would undoubtedly have them saying west, but by the end of this Activity you'll likely find a more subtle and accurate response! (i.e. southwest, northwest, it depends!) How might a change in this location offer evidence of tilt of the Earth's axis in relation to its orbit?

Explain/Explore:

Creating a complete horizon calendar would take a full year, but this activity is still interesting and informative even if it's done for just a few months. There'll be noticeable changes--just not as extreme as those from the fall to the spring equinox.

Ask students to find a location at home where they have a clear view of the western horizon. (Be sensitive to local concerns about safety, and also repeat--at every opportunity--warnings about damaging eyesight by looking directly at the Sun!) The observation point should be an easily identified place with several clear landmarks. They should make a drawing of the horizon, carefully noting--just as did ancient sky-watchers--the most prominent natural features: hills, trees, etc., but now adding contemporary markers such as church spires, radio antennas, skyscrapers! Suggest they record horizon features approximately 3-4 fist-widths, with arm outstretched, both to the left and right of where the Sun sets in the evening of their first observation. Students should record the exact location of the setting sun on their drawing once each week. Always be sure to make the observations from the same spot! Have students also record the time of sunset, and weather conditions. Have students bring their drawings into class periodically (once a month or marking period) to check their work and to discuss the changes that are occurring.

Using a magnetic compass, students should determine the directions--northwest, west, southwest--and mark these on their drawings. (Note the compass will be pointing to magnetic north, not true north, but it's okay to accept that as a uniform inconsistency, since it's not of consequence for this Activity, at least.) After some weeks or months, discuss results in class. Does the Sun set further towards the south, or the north, or in more or less the same place, as their observations proceeded?

Expand/Adapt/Connect:

Students can make a "mini-movie" of their results by creating a flip book made from several small horizon drawings to animate the changing position of sunset over time. Older students can photograph their local horizon: a panorama camera can provide a photographic horizon for the entire class. If technology permits, scan the images (only one per student is needed for the entire period of observations: it's the Sun, not the horizon, which changes position), and--as a computer technology project--use a photo editing program to create a time-lapse representation of the changing position. Simple GIF animations or Quicktime movies of the Sun's apparent movement can be created using programs such as NIH Image.

Screen "A Private Universe", which shows Harvard students having a hard time grappling with the reasons for the seasons. (Order from, Annenberg-CPB Project, 800-965-7373, $39.95)

Create a calendar using the information collected in this activity.

Similar activities can be found in "Project STAR: The Universe in Your Hands", (Harvard-Smithsonian Center for Astrophysics, Kendall Hunt Publishing) and in the "Project ASTRO" Resource Notebook, Astronomical Society of the Pacific.

If you have questions about implementing these Activities, the DISCUSS-SUN online forum has answers! No, they aren't already written down as an FAQ, but as you'll see from the introductions posted by several participants, there's a wealth of experience out there! This community will be happy to share tips no matter how "connected" your class, nor what grade level you teach.

LFSUN will post student results online (pictures of sunset horizons, timelapses, flip books, etc.), as the LIVE FROM THE SUN site "rises" and new ideas "dawn". Jump in: we think, you'll have a ball!

Suggested URLs:

http://hea-www.harvard.edu/ECT/the_book/Chap2/Chapter2.html#oots
Information about Earth's orbit; includes simple classroom activities.