PASS Vol 12

Stonehenge

Solar Motion Demonstrator

Materials

• Solar Motion Frame and Horizon Disk cutout sheets (photocopy masters on

page 32 and 33)

• Photocopy paper or heavy card stock sufficient for providing each student

with one Solar Motion Frame and one Horizon Disk (using blue paper for

the frame and green for the disk makes an attractive product)

• One long (1 inch) brass paper fastener (the type with spreadable flat prongs)

for each student

• Manila file folders (one for every student)

• Rubber cement or glue stick (can be shared by 2 or more students)

• Scissors for every student. (If you will be cutting these out for the students,

you may want to use a hobby knife or retractable-blade paper cutter which

can cut more accurately)

• Optional: spray rubber cement instead of gluestick (available from art supply

stores)

• Optional: newspapers if you are using spray glue, or will be cutting with a

hobby knife

Before Class

It takes more time to read these instructions than to make a Solar Motion

Demonstrator, so don’t let the number of steps put you off.

If you want to save time and the gluing in this section, you can buy very low

cost classroom kits, attractively printed on heavy color stock, with one finished

device and all materials for 24 students, from:

The Science Source

P. O. Box 727

Waldoboro ME 04572

Phone: 207-832-6344

As you can see from the templates on pages 32 and 33, two pieces are needed

for each device: the Solar Motion Frame and the Horizon Disk. These pieces

must be mounted on a stiff backing. This can be achieved by gluing the Solar

Motion Frame to a double thickness of manila file folder material, and by gluing

the Horizon Disk to a single thickness of manila file folder.

As an alternative, you can copy the templates onto heavy card stock. The Solar

Motion Frame then needs to be glued to only a single thickness of manila file

folder, and the Horizon Disk does not need to be mounted at all.

1. Make enough copies of the Solar Motion Frame page and the Horizon Disk

page so that each student will have one frame and one disk. If possible use

blue paper. To make an even more attractive model, copy the frames on blue

paper (to represent the sky) and the disks on green paper (to represent the

Earth).

Note

The Solar Motion Demonstrator

was designed by Professor

Joseph L. Snider of Oberlin

College. The design and

directions for use are copy-

righted by Professor Snider.

You may reproduce them as

needed for your own class-

room or planetarium (but not

for commercial purposes).

From paper, glue, and a

brass fastener you can

build a remarkably

powerful device which

accurately models the

apparent motion of the

Sun, any time of year, from

any place in the northern

hemisphere of Earth. It’s a

simple, direct way to learn

the pattern of the

changing solar rising and

setting points—just what

the builders of Stonehenge,

according to Gerald

Hawkins, wanted to mark.

You can go far beyond

Stonehenge, however, and

see how the Sun moves as

seen from the Equator, the

North Pole, or your own

hometown.

You can do the next three steps yourself to save time in class, or let your

students do this themselves.

Spray-on rubber cement adhesive, available from art supply stores, is the

fastest way to apply glue, but use this in a well-ventilated room, with lots

of newspaper under your work to catch the excess spray. Brush-on rubber

cement is cheaper but also requires a well-ventilated room. Glue sticks are

an inexpensive, non-toxic, alternative.

2. Glue the Horizon Disks to a single thickness of manila file folder stock.

3. Glue the Solar Motion Frames to a stiffer backing material, made by gluing

two pieces of manila file folder material together.

4. Using scissors or a paper cutter, separate the Solar Motion Frames and the

Horizon Disks, so that you can pass out one of each piece to each student.

The final trimming and assembly should be done by the students.

Solar Motion Demonstrator

Stonehenge

Solar Motion Demonstrator Frame Piece:

Master for Duplication

Solar Motion Demonstrator Horizon Piece:

Master for Duplication

Stonehenge

Solar Motion Demonstrator: In Class

Part 1: Making the Solar Motion Demonstrator

1. You are going to make a remarkable device that accurately models the motion

of the Sun as seen from any place in the Northern Hemisphere, at any time

of the year.

Give each student a Solar Motion Frame piece and a Horizon Disk piece.

Hand out scissors and glue.

Go through each of the steps below, allowing time for each student to

finish before moving to the next step.

2. With scissors cut out the Solar Motion Frame along its circular outline.

3. Carefully cut out the portions of the Frame marked “Remove” using scissors,

a hobby knife, or paper cutter blade.

4. Crease the frame along a straight line passing through the hinge fold line

(Folds 1 & 3: dividing the Frame vertically), by resting it against the sharp

edge of a table or counter top. Line the Frame up with the edge of the counter

top and rub it with the back of your scissors or other hard object until an

indented groove is visible. Turn the Frame over and make an indented groove

on the other side as well.

5. Repeat this creasing process for the short fold line (Fold 2) below the “Glue”

section of the Frame.

6. Fold the Frame along the creased lines (Fold 1) so that the month half of the

Frame swings all the way around to touch the latitude half of it. Repeat,

pivoting the month piece in the opposite direction.

7. Fold the flap marked “Glue” (Fold 2) away from you and down as far as it

will go, as seen from the printed side of the Frame. Bring it back to its original,

flat, position.

8. Fold both the flap marked “Glue” and the quarter-circle below it with no

printing on it (Fold 3) away from you as far as they will go, until the backside

of the blank quarter-circle hits the backside of the Frame. Bring them back

to their original, flat, position.

9. Use scissors to cut out the Horizon Disk along its circular outline.

10. Cut a small slot in the side of the Horizon Disk at the position of North.

This slot should not be any wider than the cardboard is thick, and should be

approximately 3 mm (1/8 inch) long.

11. Apply rubber cement or glue to the portion of the Frame labelled “Glue.” Press

the northeast quadrant of the disk against the glued portion of the Frame. Position

the disk so that its north-south line lines up with the frame’s hinges, and the

mark for West is positioned over the 90-degree mark on the Frame. Make sure

that the outer edges of the disk and Frame are accurately aligned. The correct

alignment of Frame and disk is essential to the working of the device.

12. When the glue is dry pivot the disk on its hinge away from you through 90

degrees, and then slip the slot over the latitude scale. Make sure that the plane

of the disk is perpendicular to the plane of the Frame.

Step 11

Step

Steps

5 & 7

Steps

4 & 6

13. Slip a paper fastener over the piece marked “MONTH,” so that the

head of the fastener is on the inner edge of the piece. Bend the head

so that its plane is perpendicular to the plane of the piece. Bend one

of the paper fastener’s prongs around the edge of the piece so that its

end lies flat against the front of the piece. Bend the other prong around

and over the first one, so that its end lies flat on top of the first prong,

behind the piece. The paper fastener should fit snugly around the

piece, and also be easily moved to cover the appropriate date on the

“MONTH” piece.

Your “Solar Motion Demonstrator” is finished!

Part 2: Using Your Solar Motion Demonstrator

How the Solar Motion Demonstrator models the Sun and the Earth:

• The “Horizon Disk” represents a piece of the surface of the Earth. You can

imagine a tiny observer (represented by the black dot in the center), able to

look out at the horizon in any direction, including North, East, South, and

West.

• The round head of the brass paper fastener represents the Sun.

• The swinging “Month” arm of the Frame has two functions. Setting the Sun

marker at the desired month adjusts for the time of the year. Swinging it

from one side to the other (preferably East to West) moves the Sun in its

apparent daily path over the Earth.

• The “Latitude” part of the Frame is used to adjust the Horizon Disk to set

the imaginary observer at any latitude from the Equator (0°) to the North

Pole (90°).

To use the Solar Motion Demonstrator, pivot the Horizon Disk along the

North-South axis so that the right hand side of the disk moves away from you

through 90 degrees. Line up the slot in the Horizon Disk with the edge of the

Frame where it is labeled “Latitude.” Slip the slot in the Horizon Disk over the

Frame and align it with the latitude of your location (or one you may be

interested in). The Horizon Disk must be perpendicular to the latitude part of

the Frame. Next, slide the “Sun” along the outer rim of the Frame to the

appropriate month.

The edge of the Horizon Disk represents the visible horizon for some

imaginary person standing at the black dot in the center of the disk. To see the

path the Sun makes across the sky for that particular latitude and time of year,

swing the month portion of the Frame completely from the “East” to the “West”

as marked on the Horizon Disk.

Compare the location of the sunrise and sunset at different times of the year.

How does the length of day change with the seasons? At what latitude must you

be so the Sun does not set on the longest day of the year (the summer solstice)?

What would the Sun’s motion look like if you lived at the North Pole?

You can answer these and many other questions with your Solar Motion

Demonstrator.

Solar Motion Demonstrator

Stonehenge

Part 3: Activities

1. Where Will the Sun Set?

Hold the device in one hand so that the Horizon Disk is horizontal. Imagine

that you are very small and standing at the black dot at the center of the

Horizon Disk. It would look like a large open field with a clear horizon all

around you. The geographical directions of North, East, South, and West are

marked around the horizon. With your other hand, smoothly pivot the piece

which carries the paper fastener “Sun.” As the head of the paper fastener rises

above the plane of the Horizon Disk, it represents sunrise and the beginning of

daytime in the imaginary world of the Horizon Disk.

When the head of the paper fastener dips below the plane of the Horizon

Disk, it represents sunset and the beginning of nighttime. The perimeter of the

Horizon Disk is marked in 10-degree increments. You can read the direction

to the point on the horizon where the Sun sets directly from the Horizon Disk.

For example, if you are at 40 degrees north latitude, and it is late June, the

Sun will set about 30 degrees to the north of west. Use your device to check

this example. If you can, take the device outdoors at sunset. Align the Horizon

Disk so that “N” on the disk points toward true North. Keep the Horizon Disk

horizontal and raise it to eye level. Sight along the line joining the central black

dot and the paper fastener head when it is located at the sunset position. This

line should point to the place on the horizon where the Sun will set.

Compare the position of sunset where you live with sunset at Stonehenge (51

degrees north latitude). On a given day, does the Sun set further to the North?

South? Is there any day at which the Sun sets at the same place for Stonehenge

and for you? (Hint: there are two days of the year when the answer is yes.)

2. How High is High Noon?

As you swing the “Sun” around, it gets higher in the sky above the horizon.

This is its “angular height” above the horizon. If you imagine yourself to be at

the location of the black dot, facing the Sun, the angular height of the Sun is

the angle between your line of sight to a point on the horizon directly beneath

the Sun and your line of sight to the Sun. The Sun reaches its greatest angular

height at a time halfway between the times of sunrise and sunset; this time is

not noon on your clock—it depends on where you are located in your time

zone, whether or not you are on daylight savings time, and on details of the

Earth’s motion around the Sun.

By using your Solar Motion model, you can get a sense of how large this

maximum angular height is for various times of the year.

3. Where will the Sun Rise?

Answer this question in the same way that you found where the Sun sets. Try

using the device some day at sunrise, sighting across it to check that the Sun

actually rises where the device predicts that it will. On any particular day, the

Sun will rise just as many degrees north or south of East as it sets north or south

of West.

Solar Motion Demonstrator

4. Is Daytime as Long as Nighttime?

Pivot the piece carrying the “Sun” at a constant rate over its entire range. This

corresponds to one rotation of the Earth, which takes 24 hours. Notice that the

Sun lies above the horizon for part of this motion (daytime) and below it for

the remainder (nighttime). You can determine the relative lengths of day and

night in this way.

5. When are Day and Night Equally Long?

Use the device to show that on two particular days of the year, the Sun rises

due East and sets due West for any latitude. Find the two months in which these

days occur. These days are called the “spring equinox” and the “fall equinox”

and are the only two days of the year when days and nights are of equal

duration. The word “equinox” comes from the words meaning “equal night.”

Answer:

The two equinox days occur in March and September.

6. When Will the Noon Sun be the Highest or Lowest in the Sky?

Use the Solar Motion device to find the month in which the largest angular

height at noon occurs. In which month does the smallest angular height at noon

occur? Also, in which month does the longest day of the year occur? In which

month is the shortest day of the year?

Answers:

Largest angular height at noon and longest day of the year is in June, at the

summer solstice. Smallest angular height at noon and shortest day of the year

is in December, the winter solstice.

The word “solstice” comes from the words meaning “Sun stands still.” Most

of the year the rising and setting positions of the Sun are changing, moving

further towards the north or south depending on the seasons. On the solstices,

the rising and setting positions stop their motions north and south, and then

head back in the opposite direction.

7. Why Does the Earth Have Seasons?

Move the paper fastener “Sun” up to its June position. Pivot the “Sun” and

observe the relative lengths of day and night and the maximum angular height

of the “Sun.” Do the same with the “Sun” moved down to its December

position. This demonstrates the two most important factors responsible for the

seasons: the period of time over which the Sun’s rays strike the ground (the

length of day), and the angle at which they strike the ground.

8. Can You Always See a Sunset?

Actually, there are places on Earth where the Sun doesn’t set. Explore the

range of latitudes and times of year for which the paper fastener “Sun” remains

above the Horizon Disk as you pivot it through an entire rotation. This

corresponds to a 24-hour day, with the Sun still above the horizon at midnight.

The phrase “land of the midnight Sun” is often used to describe the places where

Stonehenge

this occurs. For an observer anywhere north of the “Arctic Circle” (about

° latitude) the Sun will not set on at least one day of the year.

9. When and Where Will the Sun Pass Directly Overhead?

A point in the sky directly over your head is called the zenith. To find out

when and where the Sun passes through the zenith, move the “Sun” to a

position late in June and pivot it through its daily motion to see if it passes

directly overhead (assuming that you are at the location of the black dot at the

center of the Horizon Disk). Change the latitude setting of the Horizon Disk

until you find a latitude at which the Sun passes through the zenith for an

observer at that latitude. Explore the range of latitudes and times of year for

which the Sun passes through the zenith.

Answer:

For an observer north of the “Tropic of Cancer” (at about 23

degrees north

latitude) the Sun will never pass through the zenith. People who live along the

Tropic of Cancer can see the Sun at the zenith only in June at the summer

solstice. For lower latitudes than this, the Sun will pass through the zenith on

only two days of the year. Can you tell approximately which days these are?

South of the equator, the behavior is similar, but the order of months on the

Solar Motion Demonstrator would have to be reversed for southern latitudes.

Observers along the Tropic of Capricorn (at 23

degrees South) see the Sun

at the zenith only in December on their summer solstice. People South of the

Tropic of Capricorn never see the Sun at the zenith.

10. What Path Does the Sun Take at the Equator?

Set the Horizon Disk to a latitude of 0°. Imagine that you are an observer

positioned at the black dot at the center of the Horizon Disk. Vary the time

of year and see how the path of the Sun across the sky changes.

What can you say about how the rising Sun appears to move in relation

to the horizon? Notice that the setting Sun moves in the same way. At

what times of year does the Sun pass through the zenith?

Answer:

March and September (the equinoxes).

11. What is the Motion of the Sun for an Observer at the North Pole?

Set the Horizon Disk to a latitude of 90°. Again, imagine that you are

positioned at the black dot at the center of the Horizon Disk. Vary the time

of year and see how the path of the Sun across the sky changes.

What can you say now about the motion of the Sun in relation to the

horizon? Do you see that there will be six months of light and six months

of darkness at the North Pole?

12. Would Stonehenge Work if it Were Moved to Your Home Town?

Set the Horizon Disk for the latitude of Stonehenge, 51° north latitude. Write

down the rising and setting positions of the Sun for the summer and winter

solstices. Now set the Horizon Disk for the latitude where you live. Again record

the rising and setting positions of the Sun for the summer and winter solstices.

Unless you live close to the same latitude as Stonehenge, you will find that

the rising and setting positions are different. To make a Stonehenge in your

hometown, you would have to redesign Stonehenge, changing its symmetry, to

make it function as a solstice marker in the way Hawkins suggests.

Ideas for Further Activities

You will be able to think of other ways in which you can use the “Solar

Motion” device to increase your understanding of how the Sun appears to move

in relation to the earth. Here are three.

1. Imagine yourself standing at the black dot at the center of the Horizon Disk.

Try holding the “MONTH” piece fixed in space with your right hand, as

you turn the rest of the device through its complete range of motion. As you

do this, think of the Sun as being fixed in space, while the Earth’s rotation

turns you around with respect to the Sun. This is more nearly the situation

in real life.

2. Try using the device as a compass. Set the “Solar Motion” model to your

latitude and the time of year. Go outside and hold the device so that the

Horizon Disk is horizontal. Pivot the “MONTH” piece and at the same time

turn the compass piece (keeping its plane horizontal) so that the “N-S” line

points in various directions. Your objective is to make the shadow of the

“MONTH” piece be as thin a line as possible, while at the same time the

shadow of the paper fastener “Sun” falls on the black dot at the center of the

Horizon Disk. When you have achieved this, the Horizon Disk will show

you the correct geographic directions.

3. Try constructing a giant Solar Motion Model. You can use a photocopier to

enlarge the Frame and the Horizon Disk. You might want to mount these on

stiffer cardboard, artists’ “foamcore” material, or plywood. You may need to

make stronger hinges out of cloth, or use metal hinges from a hardware store.

Solar Motion Demonstrator