Models organize big ideas for scientists and students; they identify and test questions and are ideal tools for thinking. The Earth/Moon Rotation orrery shows our planetary movement around the sun and demonstrates lunar orbit and moon phases when illuminated with an accompanying light.
The Parts.
Step 1. Put the seasonal labels on the corners in order: Winter, Spring, Summer, Fall. Put the two small pegs into the holes in the base.
Step 2. Put the dowel with the Sun ball into the rounded end of the arm and tightly into the hole in the slotted wheel that you put onto the base in Step 1.
Step 3. At the other end of the arm, put a large wheel on the peg sticking out the end of the arm (put the o ring on the outside to hold it on) and put the smaller wheel with the dowel in it up through the hole next to the large wheel.
Step 4. Loop the rubberband around the slotted wheels on the bottom as shown. Note there is a twist in the rubber band
Step 5. Put the last large wheel on the dowel so it rests on the other large wheel. Carefully place the earth/moon assembly on the top of the dowel and make it secure. Move the Orrery arm counterclockwise to rotate the moon around the earth.
Step 5a Detail.
Step 5b Detail.
Isaac Newton (1642 - 1727) worked out the mathematics of the movement of the planets. His contemporary, Charles Boyle, the Earl of Orrery, commissioned George Graham to build a mechanical model of Newton's ideas in 1700. Orrery's name stuck.
When Eli Whitney went to Yale in 1788, science as a subject was still new. The first Orrery purchased by Yale arrived from Germany broken. Whitney fixed it, a hint of the practical mechanical skills that would make him famous.
Models can help us answer questions. With this model, you can demonstrate the cycles of the Moon, the timing of the tides, the relative positions of the Sun and the Moon during eclipses, and the changing of the seasons. It accurately shows that the Moon is about 1/4 the size of the Earth. But all models have limitations. This Orrery would have to be much more complicated to more accurately demonstrate many other relationships. For example:
Our model's Earth is 1" in diameter.
Our model's Moon is 1/4" in diameter.
Reality: The Moon is 30 Earth diameters away from from the Earth.
So our model should show the moon 30" away from our Earth. It shows it about 3" away.
Reality: The Sun is about 109 times larger than the Earth.
So our model Earth should travel around a 109" diameter sun (about 9 feet wide.)
Our model sun is only 1.5" in diameter.
Reality: 12,000 Earth diameters (12,000 inches in our model!) would accurately show the distance of the Earth to the Sun.
Our model would need an arm with a circular radius of 1000 feet. Ours arm's circular radius is only about 10".
Certainly you can guess why we had to do this.
The model reminds us that Earth travels around the Sun.
But in reality, does it always seem that way?
We all often say, The sun rises in the morning.
But the Sun does not move. The Earth turns.
The Model shows that the Earth turns toward the Sun in the morning.
When we wake up in the morning we see the sun first in the East.
So our Earth is turning on it's axis towards the East.
Looking down on the North Pole, we call that direction counter clockwise.
The Earth also travels around the sun in a counter clockwise direction.
And the Moon travels around the Earth in a counter clockwise direction.
One turn of the Earth around its axis = a day.
One trip of the Moon around the Earth = about a month.
A revolution of the Earth around the Sun = about a year.
Explaining Changes
First, shine the light on the earth.
New Moon
Position the Moon between the Earth and the Sun.
The face of the Moon that we see from the earth is dark. A New Moon.
Waxing Moon
Move the Moon counter clockwise. The sliver of light that we see projected on the Earth
grows larger. Waxing means growing.
Full Moon
Position the Moon so that its whole face is illuminated. That's a Full Moon.
Waning Moon
Move the Moon counter clockwise again. The sliver of light we see grows
smaller. Waning means emptying.
The Moon is close enough to the Earth that its gravity pulls on the planet.
That gravity pulls on the oceans which create the flows we call tides.
That gravity also creates tides on the side of the Earth opposite the Moon.
The Moon moves as the Earth turns each day.
So the times of the tides change each day.
The Earth is tilted on it's axis 221.2 degrees.
Winter
When the Earth is tilted away from the sun, the arc of light that reaches the Northern Hemisphere is short.
The shortest day (The Solstice) is the first day of Winter.
Spring
When the Earth tilts neither to or away from the Earth, the Sun will light half the earth. Days grow longer.
Equal days and nights (the Spring Equinox) begins the season we call Spring.
Summe
When the Earth is tilted toward the sun, the arc of light that reaches the Northern Hemisphere is long.
The longest day (The Solstice) is the first day of Summer.
Fall
When the Earth tilts neither to or away from the Earth, the Sun will light half the earth. Days grow shorter.
Equal days and nights (the Fall Equinox) begins the season we call Fall.
Solar Eclipse
The Moon is 400 times smaller than the Sun.
The Sun is about 400 times farther away from Earth than the Moon is.*
So they appear to us about the same diameter.
Occasionally a Full Moon's path will cross in front of the Sun.
Some people on Earth may see the Moon block the Sun's light briefly.
We call those few minutes a Solar Eclipse.
*This Orrery shows the position of the Moon in the eclipse, but not the proportions
that make it work. Remember the Scale issue.
Lunar Eclipse
The shadow of the Earth crossing the Moon is called a Lunar Eclipse.
This must happen when the Moon is a Full Moon.
It does not happen every Full Moon because the Moon travels on a tilted orbit**
There can be two or more Lunar Eclipses in a year.
**This Orrery can show the position of the Moon in an eclipse, but not the
proportions or tilt that determine the timing.
Answer:
Approximately 28 days pass between a full moon and the next one, but the answer may not be that simple. During a full moon the earth and the moon line up on a radius drawn from the sun through the Earth. During those twenty-eight days the Earth has progressed 15 degrees further alone its orbit around the sun. Therefore, between full moons the Moon has traveled 360 degrees around the earth plus the 15 degrees that the earth has moved. (minus 15 degrees, if the orbit of the moon is opposite the orbit of the Earth) A more correct answer may be 27 days or 29 days dependent on the direction of the orbits.
Answer:
In order for the same side of the moon to face us, the Moon must rotate at the same rate that it orbits the Earth. From full moon to full moon is 29.5 days or 12.3 times in a year. The Earth orbits once in a year, which must be added to the moon’s revolution, so in the end the Moon rotates 13.3 times in a year.
Answer:
Yes, the four sides of the base model the four seasons very well. When viewed from the Earth’s North Pole, the Earth moves in a counter-clockwise direction. Therefore, the sides of the base should be labeled winter, spring, summer and fall in a clock-wise order.
Answer:
Oh, no. The Earth is modeled with a 0.9-inch diameter ball. Venus is just about the same size as the Earth and so it makes sense that it is a 0.9-inch ball as well. Mercury has a diameter that is 40% of Earth, so using the same scale it should have a diameter of .4 x .9 or 0.36-inch. The actual size of the Mercury model in 0.4 inches, which is only slightly larger than it should be. The Moon should be 27% of the Earth and it measures 0.25 inches. 0.27 x 0.9 = 0.24. That dimension is very close to the size it should be. Now, the Sun… The actual Sun is 110 times larger in diameter than the Earth. So if the Earth is 0.9 inches, the Sun should be 99 inches in diameter. Wow! The Sun should be a ball a little over eight feet in diameter (the height of most ceilings). The model is way too small for the Sun.
Answer:
The reported distances of the planets from the Sun are: Earth - 149 million kilometers, Venus – 108, Mercury – 58. The distance from the Earth to the Moon is 0.38 million kilometers. On the model the distance from the Sun to the Earth is 7.5 inches. Students can use proportions to verify the following dimensions for the model. Sun to Mercury should be 3 inches and the Sun to Venus should be 5 ¼ inches. Using this same proportion, the distance from the Earth to the Moon should be only 0.019 inches (less than 1/32nd of an inch). This dimension is not scaled correctly at all.
Answer:
Well, not exactly… The earth actual rotates 360 degrees in 4 minutes less than 24 hours. The reason for this effect is that the Earth is moving one degree each day in its orbit around the Sun. The Earth has to rotate 361 degrees between noon on one day to noon on the next day. The 360-degree rotation is called the sidereal day.
Answer:
You can determine the direction of rotation of the Earth without setting up an experiment. The sun rises in the East. Therefore, the Earth must spin counter-clockwise when viewed from the North Pole. Using your orrery mark a position on the Earth. Mark the direction toward the East. Spin the Earth in both directions and determine which direction shows the Sun in the East when the position moves from what would be the dark half (night) to the light half (day).
Figuring out the direction of orbit for the Moon may be a little more difficult. In the evening set up a stick or series of two sticks that point at the Moon. Record the time. On the next night (or subsequent nights) at the same time of day determine whether the Moon is at the same position or further to the East or West. You should observe that the Moon is further to the East. Accordingly, the Moon will rise later each night. It orbits the Earth in a counter-clockwise sense.
You can determine the direction of Earth’s orbit similarly by observing the movement of the stars from night to night. You should pick a star that is in the Eastern or Western sky. Measure whether the star moves to the East or the West. You should find that the stars move toward the West indicating that the Earth’s orbit in also counter-clockwise. This experiment requires more precise measurement and often many days between readings. Remember the Earth only moves one degree each day in its trip around the Sun.
Do you see a pattern? Most everything rotates or revolves in a counter-clockwise direction in our solar system, but not everything. Venus spins clockwise or retrograde. Can you give an explanation?
Answer:
The moon has day and night just like on Earth. However, each lasts for about 15 days on the moon. A "Moon day" last 29.5 days.
Answer:
The oceans of the Earth are pulled toward the Moon. When the Earth spins each day, the Moon moves around in its orbit too. When combining both effects, a position on the Earth points toward the Moon once every 25 hours instead of every 24. For this reason the tides are approximately one hour later each day. There are usually two sets of tides each day. The second set of tides is a rebounding phenomenon due to the specific shape and size of our oceans.
Answer:
Yes. The orbits of most of the planets including all the inner planets are very circular.
Answer:
The seasons on Earth are caused by the tilt of its axis relative to its orbit. The direction of the tilt stays the same relative to the stars as the earth orbits around the Sun. In this way the North Pole leans toward the Sun in summer and away from the Sun in winter. During summer in the Northern Hemisphere there are more daylight hours and the Sun is more perpendicular (more overhead). The seasons are NOT caused by the Earth moving closer and further away from the Sun. This orrery does not model the tilt of the earth.
Answer:
One degree represents the angle the Earth travels around the Sun in one day.
Answer:
Sunlight falls on half the Earth. The other half is in darkness. The line marking the boundary between the two is a circle perpendicular to the line connect the Earth with the Sun. Because the axis of the Earth’s rotation is tilted some 23 ½ degrees, the North and South Poles are not usually on this boundary circle. In summer the North Pole is in the sunlight side and any place in the Northern Hemisphere will spend more than half a day in the sunlight side. In fact there will be no nighttime at the North Pole at all. While the North is in summer the Southern Hemisphere will be in winter and nighttime will be longer than half a day. The affect of the tilt on the length of sunlight decreases toward the equator until when you are on the equator. At the equator daylight and nighttime are both 12 hours all year long.
Answer:
No. The Sun everywhere on Earth rises in the East and sets in the West. What is different is where the Sun appears in the sky. In the United States the Sun is in the southern half of the sky. In Australia the Sun is in the Northern half.
Answer:
The orbits of both Mercury and Venus are inside the orbit of Earth. As those two planets travel around the Sun, the furthest they can appear away from the Sun is when their position in their orbit is perpendicular to Earth. In this position Venus has a maximum angle of 35 degrees from the Sun and Mercury has a maximum angle of 21 degrees. If the Sun was just on the horizon, the highest Venus could be is 35 degrees up. In reality, to view the Stars and the Planets, the Sun must have set for some period of time – about an hour or so. An hour relates to 15 degrees of the Earth’s rotation. When that 15 degrees is factored in, the result is that Venus is not seen higher than about 20 degrees and mercury not higher than 5 degrees. By the way, you can tell the difference between the stars and the planets, because the planets all track in the same area as the Sun and the Moon (called the ecliptic) and the planets don’t twinkle.
Answer:
Knowing that counter-clockwise is the direction for both Earth’s spin and the Moon’s orbit, you can place the Moon in a position where it is just visible at dusk. The lit side of the Moon will be towards the West.
Answer:
The Moon will between the Earth and the Sun.
Answer:
The Earth will between the Moon and the Sun.
Answer:
In a full moon the Moon will be away from the Sun so the Earth will see the whole sunlit side. This position is same as in an eclipse of the Moon. However, an eclipse does not occur every time there is a full moon. The orbit of the Moon wobbles up and down. An eclipse will only occur when the Moon is directly in line with the Earth.
Answer:
In winter the tilt of the Earth is pointed away from the Sun. The Sun will be lower in the sky and shadows will be longer.
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