Objectives
- Students will measure using a variety of tools.
- Students will learn about patterns.
- Students will learn vocabulary concerning seasons.
Materials
- Outside space – Locations offering a 360° horizon view are ideal (and rare). You will need to leave markings on the ground for awhile. Find a place where they can be left undisturbed, part of the school parking lot, part of a playing field, an off site location.
- Center stake for reference point
- 50 feet of rope
- 20 to 30 marker stones or small stakes
- A compass
Procedure
Create a viewing circle (see image below).
Anchor a reference stake at the center point of the circle and place the compass on top of it.
Determine due north and place a marker at 50 feet north of the center.
Repeat the process for east, west, and south. (The rope is used as a guide to insure that all markers are equidistant from the center stake.)
Again, using the rope as a guide, place a small marker stone every few feet around the perimeter of the circle.
The center of the circle now becomes the fixed reference point and the westward facingperimeter is where you'll be placing the sunset markers.
The calendar can be started at any time, but the solstice sunsets are the most fun. (The Northern Hemisphere is the reference for the following dates. The summer solstice, which happens on June 21 or 22 each year, has the longest daylight time. It's also the first day of summer. The winter solstice, on December 21 or 22, has the shortest, and officially kicks off winter. The autumn equinox occurs on September 21 or 22; the spring equinox occurs on March 20 or 21.) Think of all the vocabulary you can teach!
Mark the point of sunset with a pole, stake, or other (not easily moved) marker.
Tag the marker with the date of sunset.
Repeat the process every seven days or so. Over the weeks and months note that the sun appears to "walk" faster at some times of the year than others.
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When you've finished (you could do this over the entire school year) you'll have a working astronomical calendar.
Additionally, you can teach students about the importance of these dates in prehistoric and contemporary religions, fitting these topics into social studies and religion curricula.
Non-construction alternatives
- Photo-op: Take a snapshot of the western skyline and tape it to the wall by a western-facing window. With a felt-tip marker, draw an arrow on the photo corresponding to the point of sunset and note the date. Repeat the process.
- Window marks: (This takes two people.) Standing at the same point in the room of a western-facing window, have the other person make a small mark on the glass where the sun sets. Note the date and repeat the process on a weekly basis.
How it works:
The principle behind an astronomical calendar is simple. The apparent rising and setting horizon point of the sun changes with each passing day. The different points correspond to differentdays of the year.
At a minimum, an astronomical calendar only requires a fixed reference point for viewing, and another fixed reference point marking the position of the rising and/or setting sun on the horizon.
In the northern hemisphere, if you were to watch a time-lapse movie of a year's worth of sunsets, you would notice that the sun appears to "walk" back and forth across the western horizon. Thewinter solstice marks the southern limit of the sun's journey, and the summer solstice is the northern boundary. Closer examination would reveal that, with the exception of the two solsticeextremes, every other point on the horizon is crossed twice during the course of the year, once on the southern march and again on the northern return.
At the time of the winter and summer solstices, (around December 22 and June 22) the sun is directly overhead at either the Tropic of Capricorn (winter) or the Tropic of Cancer (summer).
