Training Manual Format
The Seasons Interactive
Brief Summary
This exhibit, a portable free standing table, allows a facilitator to illustrate why we have four seasons. A six-inch moveable Earth globe is mounted so that half the Earth is always half illuminated by a flashlight as the Earth moves around the sun. Also, Earth always retains its 23.5 degree tilt. In addition The Seasons Table can be used to expand the conversation with visitors into other related areas such as eclipses, important geographic lines on the globe such as the Arctic Circle and the Tropic of Cancer, and precession of the equinoxes and the North Star.
It is worth noting that this cart was originally conceived and prototyped by the Monday Morning and Wednesday Afternoon Galaxy Guide teams.
Equipment Required
|The Seasons Table, an exhibit similar |[pic] |[pic] |
|to the Phases of the Moon table, but | | |
|smaller, can be set up and used by one | | |
|person. | | |
| | | |
|Props: | | |
|Graph paper | | |
|Moon on a stick | | |
|Toy top. | | |
| |Facilitating with the Seasons Table |Setting up the Seasons Table. |
Set-Up Procedure
• Roll the cart to a place near light but not flooded with light. You want the globe’s sunny side to be distinctly different from the shaded side.
• Remove the four legs from their holders, place them into their sockets and tighten the knobs. (Note: the knobs have to be tightened up snuggly so that the legs will not fall out when the table is tipped.)
• Twist the propeller-like stays that hold the table on the cart, and gently tip it onto the floor.
• Note that the table is stored so that the month of May is at the top with the globe held by a bungee cord.
• Remove the bungee that holds the globe in place.
• Once the table is upright, rotate it so that December is on the north side towards the Mars diorama. This way, the axis of the Earth points at approximately true north.
• Keep the props handy.
Main Teaching Points
Story #1: Interpreting the physical facts of the model. (A prerequisite to all the stories.)
1. A day equals one complete rotation of the Earth on its axis.
2. A year is represented by the Earth circling the table once.
3. The table surface represents the plane of the earth’s orbit around the sun.
4. The opposite season to fall is spring. The opposite of winter is summer. (Many school age children do not know this.)
5. The tilt of the Earth globe in its holder represents the earth’s axis leaning over. The tilt of the axis is 23½ degrees (as compared to standing straight up.) This degree of tilt never changes.
6. The two equinoxes occur on or about March 21 and September 21. The summer solstice (also called mid-summer’s day) occurs on or about June 21. The winter solstice (aka mid-winters day) occurs on or about Dec 21. These four dates change because we insert a leap year day every fourth year.
Story #2 The causes of the seasons
1. The Earth goes around the sun so that two things always remain constant: The tilt of the axis at 23.5 degrees, and the fact that half the Earth is always in light and half in the dark.
2. The seasons are caused by the shifting of the amount of light that is received by each hemisphere of the Earth as it orbits the sun.
3. The tilt of the axis contributes to the seasons in two ways:
a. Longer summer days allow for the collection of more energy from the sun.
b. The light hitting the surface in summer is concentrated onto a smaller area of the surface than the same amount of energy in the winter, when that fixed amount of energy is distributed over a greater area.
4. The daily high temperatures around the spring equinox day, March 21 are lower than those around September 21 (the fall equinox date) because of thermal inertia, the tendency of the Earth to retain its temperature. The hottest week of the year in Colorado is in July, four weeks after midsummer’s day.
Story #3 Eclipses
1. The small moon prop that resembles a lollipop is nearly true to scale of size of the earth, but not to the distance scale. It should be out at 30 Earth diameters away. This is a surprisingly large distance of six paces.
2. Half of the moon is always illuminated, even if we don’t see that half.
3. Eclipses of the moon happen when the moon passes into the Earth’s shadow. The process takes about three hours to complete. Total lunar eclipses occur about every year and a half, though partial lunar eclipses are three times as common.
4. A solar eclipse happens when the shadow of the moon falls on the earth. (The scale on our model here is not realistic because in reality the moon should be placed over six paces away from earth.) The moon’s shadow in our model covers half a continent, whereas in reality it is only about 1200 miles across, or as big as the letter O in North America on the globe.
Another effect that is hard to show is that the moon’s orbit tilted at five degrees compared to the plane of the earth’s orbit around the sun. This tilt of five degrees explains why eclipses of the sun and moon do not happen every month. With this tilt of the moon’s orbit, five out of six times (on average) the moon’s shadow passes above or below the plane of the earth’s orbit. Likewise, the moon, on the anti-solar end of its orbit, passes below the earth’s shadow so no lunar eclipse occurs. The tilt reduces the necessary alignments for eclipses to happen.
Story #4 The various lines on the globe.
1. At the North Pole, if the Earth had a perfectly smooth horizon the sun would set on the evening of the fall equinox and not rise again till the morning of the spring equinox. Except for a few weeks of twilight before sunrise and after sunset, the North Pole experiences total darkness for half the year.
2. At every point on the Arctic Circle, the sun stays above the horizon for at least one full 24-hour day. At a point a mile south of the Arctic Circle, the sun sets for at least a minute or so, even on the summer solstice.
3. On the tropic of Cancer, a stick stuck straight into the ground (perpendicular to the surface) will cast no shadow on one day of the year, the summer solstice. South of the Tropic, the sun will pass over head two days a year. At the equator, the sun passes overhead at noon on the equinox days.
4. The same physical events occur in the southern hemisphere with the Antarctic Circle and the Tropic of Capricorn, but in the opposite seasons from the northern hemisphere.
Story #5 Precession
1. The Earth spins like a toy top, or a coin that has been set on its edge and spun. This turning motion, called precession, happens at a slower rate than the primary spinning motion.
2. The Earth precesses in one giant circle every 26,000 years which equals about 1 degree every 70 years.
3. The three effects of precession are 1) to change what season that we see the constellations in 2) to change the time of year that the Earth is closest to the sun (perihelion point) or farthest from the sun (aphelion point) and 3) to change which star the earth’s axis points to. The tilt of the earth’s axis does not change, but only the star that lies above the Earth north pole.
|[pic] |Today the star Polaris lies above the earth’s North Pole. In |
| |3000 BC and again in 23,000 AD the star above the earth’s axis|
| |will be Thuban. The Egyptians aligned some of their buildings |
| |with Thuban. By about 15,000 AD, Vega will be a North Star, |
| |but not as good a North Star as Polaris, because it lies |
| |farther from the path of the North Celestial Pole than |
| |Polaris. In 21,000 AD, Deneb will be another not-so-good North|
| |Star. Finally, 26,000 years from today, Polaris will again be |
| |the North Star. |
Educational Strategy
The concepts involved in understanding the two main causes of the seasons look deceptively simple. In fact, the explanation of the seasons probably confuses more adults and children than any other space concept. This exhibit allows the facilitator to tell five “stories,” (that is, five presentations and facilitation of related facts, observations and activities).
These stories range in difficulty from
#1. Interpreting the physical facts of the model.
#2. The causes of the seasons
#3. The causes of lunar and solar eclipses
#4. The physical significance of the lines on the globe, e.g., the Arctic Circle and the Tropic of Cancer.
#5. Precession. This wobble affects three things. (See above Story #5 for details.)
Suggested ways of presenting demo
Try this:
If a visitor is at an early stage of learning about the seasons, (a child or naïve adult) use only Stories #1 & #2.
• Illustrate what a year is, then what a day is and then a day and year combined.
• Illustrate the concept of opposite seasons and the equinoxes and solstices on the calendar.
• Establish what tilt of the earth’s axis means, and illustrate by moving the globe around the circle that it does not change.
• Move the globe to the spring equinox. Have visitors observe that the Earth is always half in the light and half in the dark, and that only on the equinoxes days do both the north and south poles get light at the same time. Otherwise, either the North Pole or the South Pole get sunlight, but not both.
• If the axis of tilt and the illumination of the Earth don’t change, what does? Answer: In summer, the light is not distributed evenly. One hemisphere gets more light than the other and this makes it warmer there.
• Use the graph paper to show that when the rays of the flashlight hit the paper perpendicularly, the light spot is smallest and the energy is most concentrated. As you tilt the graph paper, the light falls on more and more squares. This means that the energy on any square is now less concentrated per square foot than the light of summer which is more concentrated. (be sure to define “concentrated” in kid-friendly tenr, e.g. butter on toast.) Secondary factors aside, the more concentrated the light, the higher the temperature.
If a visitor is at an intermediate stage of learning about the seasons: Review Stories #1 & #2 in brief, then draw out of the visitor the physical meaning of eclipses (Story #3) and/or the lines on the globe (Story #4)
For the advanced visitor, draw out the facts of precession mentioned in Story #5.
Operating Tips
• Here’s a great question to facilitate a discussion: Where would you have to go on Earth to get the maximum number of hours of sunshine in a year. (ANS: Everywhere on Earth is identical in hours of sunlight per year, barring clouds and horizon obstacles such as mountain ranges.)
• It is important to keep from mixing stories together. Do all of one story along with its enabling concepts, before moving onto another story.
• Don’t try to tell all the stories to one set of visitors.
Questions and Answers
Is the model to scale? How far is the Moon from Earth?
The Moon is 240,000 miles from Earth, or about 30 Earth diameters. Demo: Show how far away the Moon would be, and describe where the Sun would be. (Sun is 93 million miles away, about 12,000 Earth diameters! Before you do the demo, measure out the distance of 30 globes so that you know where in Space Odyssey the Moon would be. During the demo, ask a visitor to walk to where he or she thinks the moon would be. They will be surprised when they find out the actual distance.) Explain that at this scale, the Sun would be at the City Park Lake house ( ¾ of a mile away) about three stories in diameters..
What about eclipses?
A LUNAR ECLIPSE happens when the Earth comes between the Moon and the Sun. Demo: Move Moon through orbit until it is on opposite side of Earth from Sun. Ask what phase Moon must be in for lunar eclipse to happen (full moon). A SOLAR ECLIPSE happens when the Moon passes between the Earth and the Sun. On Earth, a solar eclipse can be seen only along a narrow path thousands of miles long on Earth. Demo: Move Moon through orbit until it is on the same side of Earth as Sun. Moving Moon slowly, show area on Earth that would experience solar eclipse. Ask visitors what phase Moon must be in when solar eclipse happens (ANS: New moon).
Why don't eclipses occur every time there is a new Moon?
The plane of the Moon's orbit is tilted at five degrees from the plane of the Earth's orbit around the Sun. This disturbs the critical alignments that make eclipses happen, reducing them to only at most a few a year rather than every month.
Potential Problems
• One of the difficulties of the concepts of seasons it that people (and kids in particular) don’t know the supporting and enabling concepts involved. For example, the opposite season of SPRING is FALL. Even some sixth graders don’t answer this immediately. The Seasons Table is a way to teach verbal concepts, such as opposite seasons, day and year using a visual representations. These enabling concepts must be acquired before any understanding of the causes of season really sinks in..
Background materials (websites, videos, articles, digital collections links)
#1: Interpreting the physical facts of the model.
#2. The causes of the seasons.
#3: The causes of lunar and solar eclipses.
#4. The physical significance of the lines on the globe, e.g., the Arctic Circle and the Tropic of Cancer.
#5. Precession.
Self assessment suggestions
After facilitating the Seasons Table several times, complete the checklist and rubric below by highlighting the box that best describes your performance. Have your team leader observe your demo then complete an identical rubric. Discuss your presentation technique with your team leader along the lines of the rubric.
A. Checklist of pre-requisite skills for facilitating Seasons Table.
| | Knows how to store the table in the main storeroom. |
| |Understands and can explain clearly the enabling teaching points of how the sun appears to move: daily motion, and seasonal motion. Story |
| |#1. |
| |Understands and can explain clearly the main teaching points of each of five stories: |
| |#2: Causes of the seasons |
| |#3. Eclipses |
| |#4 Lines on the Globe |
| |#5 Precession |
| | |
| | |
| | |
| | |
B. Rubric for Galaxy Guides— SEASONS TABLE DATE________ PRESENTER_________
|QUALITY LEVELS ( |OK |COOL |WAY COOL |
|TRAITS( | | | |
|Individualizing visitor |Can run the activity by giving clear |Can respond to visitors on different |When responding to a curious and advanced visitor, |
|experience |step by step instructions to visitors|levels: For children concentrating on the |can use correctly and explain clearly the terms, |
| |of all ages |"arts & crafts" angle, and for interested |"sidereal," "mean solar time" and place the sundial |
| | |adults, the apparent motions of the sun |in a historic context |
|Attitude durability |Remains pleasant and patient |Remains pleasant and patient throughout |Finds ways to self-renew, continues to enjoy |
| |throughout shift, even when repeating|shift, enjoys helping visitors, does not |responding to visitors with enthusiasm while |
| |the same statements over and over |get (visibly or noticeably) tired during |recognizing the uniqueness of each new visitor |
| | |shift | |
|Sparks visitors’ |Directs visitor to digital collection|Asks stimulating questions to engage the |Understands content and explains on appropriate |
|curiosity |or to other staff with more knowledge|visitor at heightened level |level. Opens new subjects for inquiry |
|Drive behind |Asks leading questions |Draws visitor into asking questions |Facilitates an open inquiry; lets visitor take lead |
|conversation | | |in asking questions |
|Clean up |Cleans up all materials used and |Cleans up all materials used and stows them|Cleans up all materials used and stows them properly |
| |stows them properly |properly | |
|Improves demo over time |Discusses demo with peers and |Works with peers on evaluation, implements |Develops written goals and strives to meet these |
| |implements new techniques |new techniques |goals, eg, “Raise Knowledge of exhibit from OK to |
| | | |COOL by Sept.” or “Raise all OK’s to COOL by August” |
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