Earth-Moon-Sun Notes
1. For the first meeting, we try to explain the way Earth's rotation
causes Sun to move in sky, leading to night and day, and the fact that
the time of day is different in different places on Earth.
- First spend 30 minutes with a globe to represent Earth, an overhead
projector representing the Sun, and a little figurine you can put
on the Earth to represent people. Explain that a globe is a small-scale
model of the Earth. Explain that in our pretend game for the day they
are huge (bigger than Earth) and out in space. They can pretend they
have spacesuits for air. But space is dark (turn off lights). Only
light around here comes from Sun (turn on slide projector). If you look
at Sun you get blinded, so don't. But when sunlight hits Earth, you can
see the Earth. Moreover, people on Earth can now see stuff around them
because sunlight illuminates it. But not all people on Earth. Note that
only half of Earth illuminated. People on that half can see around them;
if they look up (use figurine) they see the Sun. On other side of Earth,
it's dark and Sun is not in sky. Let them tell you this is day/night.
Now ask them how this situation changes. Get to Earth rotating slowly.
Takes a whole day and night to go around - 24 hours. Show them Durham and
go through a day and a night in Durham, showing where the Sun seems to be.
Explain that Sun looks like it moves in sky - rises, sets, etc. - just as
when on carousel things *off* the carousel seem to be spinning. Earth as
a merry-go-round (you can tell them we move at 800 mph as it spins if
you think it will not take you on a huge tangent). Finally, show how
different places on Earth have a different time of day at any given time.
If there are kids in the class who have flown far enough to notice (ask
teacher about this in advance - it may be her opportunity to let some
foreign student who never talks shine) let them talk about jetlag and
explain how this works.
- Following these (rather dense) 30 minutes they will do a follow-up
activity with you and the teacher helping out and monitoring. This
is likely to be a good group activity but how they do it is up to the
teacher. We will hand out papers with several configurations of
a Sun, an Earth (each a circle), with four points marked on Earth.
One of these will be red and will represent Durham. Sun will always
be on left (say) but Earth will be rotated, so time in Durham is
different. Their first goal will be to color (in yellow?) side
of Earth illuminated by Sun. Then they try to figure out if it is
day or night in Durham. Then to guess what time it is in Durham.
Finally, they can go back and try to figure out what time it is
at the other points marked on Earth in each of the configurations.
This should help nail the concepts. It will also come in handy
later when we use the same trick to understand Moon phases.
Name ______
Day and Night
In each of these pictures, we see the Sun on the left and the Earth on the right. We are looking down at the Earth from above the North pole. We have marked four places on Earth as 1,2,3,4 to make it easier for us to see what happens as Earth rotates.
- At 12 noon, you should be able to see the Sun by looking directly overhead.
a) Label the Earth and the Sun.
b) It is daytime on about half of the Earth, where the sunlight can reach. Color this half of the Earth yellow.
c) Draw a small stick figure at one of the four numbered points so that this person can see the Sun by looking straight up.
d) At which of the numbered points is it noon in the picture?
______
1
2 4
3
- As the Earth turns, our stick figure is carried with it. It stays at the same spot at position #2. This picture shows what happens about two hours after the first picture.
a) Label the Earth and the Sun.
b) It is daytime on about half of the Earth, where the sunlight can reach. Color this half of the Earth yellow.
c) Draw the stick figure from question 1 where he would be now.
d) Can he see the Sun?
e) Is it straight up overhead?
______
1
4
2
3
3
- The Earth continues to turn, carrying the little man with it. It says on position #2
a) Label the Earth and the Sun.
b) It is daytime on about half of the Earth, where the sunlight can reach. Color this half of the Earth yellow.
c) Draw a stick figure where our person would be now.
d) Can he see the Sun?
e) What time do you think it is where the figure is now?
f) How many hours have passed since question 1?
______
3
4 2
1
- The Earth continues to turn. What happens now?
a) Label the Earth and the Sun.
b) It is daytime on about half of the Earth, where the sunlight can reach. Color this half of the Earth yellow.
c) Draw a stick figure where our person would be now.
d) Can he see the Sun? Is it overhead?
e) What time do you think it is where the figure is now?
f) How many hours have passed since question 1?
______
2
3 1
4
- Now look at this picture. Not all the points are numbered.
a) Add in the missing numbers and our person.
b) What time is it where the person is?
c) How much time has passed since question 1?
______
1
4
- Go back to the pictures.
a) In which picture is it noon at point number 3?
b) In that picture, what is the time at point number 2?
c) Can you write next to each numbered point in each picture what time it would be at that point?
Seasons
This week we will be talking about the seasons and the Earth’s motion around the Sun.
· We start with a reminder of the stuff we talked about last time – day and night and the Earth’s rotation. Use a bare bulb as the Sun. Set it up in the middle of the room so that you are able to walk around it to demonstrate the Earth orbiting later on. An ideal setup would have the kids sitting close to each other in one area of the class – some teachers are better set up for this than others, so we will need to improvise here. Use your little toy to show positions on Earth, go through where it is day and where night. Remember to turn Earth West to East (which looks counterclockwise when you look down at the North pole)! Mention our story about living on a merry-go-round called Earth, moving at 1000 mph around equator, so that everything off Earth seems to be rotating.
· While on this subject, we may as well bring latitude into the story. Ask them where on Earth you can ever see the Sun directly overhead. In our current model the answer is the Equator. To see this dramatically, put your figure at the North pole and have them find out that he now sees the Sun on his horizon, and its motion for him is completely horizontal. Show them how at intermediate latitudes he sees the Sun move in the sky in a circle tilted by his latitude. It is not necessary to go into the mathematics of the angles here, the point it that the farther from the equator you go, the flatter the Sun’s motion in the sky and the lower it stays.
· Note that nights are cooler than days (makes sense, no Sun). Ask them, holding Earth vertically (no tilt on the axis) whether light or dark is longer. There will be differing answers here, including I am sure some referring to seasonal change. Try to get them to admit that as your model stands now, everyone on Earth should see 12 hours of light and 12 of dark, except maybe at the poles where you get perpetual twilight.
· They will likely have told you already that this is not the way things are, so see if they can tell you why they think this is. You are likely to get a correct answer here, but do not assume they all get it because one does. Start by tilting the Earth (by about 45 degrees) so the Northern hemisphere faces them. Point out how most of what they see is the Northern hemisphere. Show how as you turn the Earth about a tilted axis, there are some points (down to latitude 45) that they can see at all times; some points (latitudes near the equator) they can see for part of the time; some parts of Earth they do not see (south of latitude –45). Note that as Earth turns, points in the North are visible for more than ½ the time and points in the South for less.
· Now make the connection to the Sun and the tilt of the Earth’s axis relative to its orbit. Start with the Northern hemisphere pointed towards the Sun; exaggerate the tilt as above. Show them that days are longer than 12 hours in the North, shorter in the South. Make a connection to more sun means warmer. This is summer in the Northern hemisphere, winter in the South. Show them how north of the arctic circle the Sun does not set, just as they could see points near the pole at all times. South of the Antarctic circle the Sun never rises.
· What happens to change the seasons? Try tilting the Earth in another direction. Now South faces Sun, so this would be winter for us, and summer in the South. Is this what happens? It could be but it isn’t. In fact, Earth’s axis points in same direction at all times. What does change is where Earth is relative to Sun. Our merry-go-round ride is even more interesting. Go 180 degrees on orbit, to get to point where it is winter in north, summer in south. Get them to guess what month this is. Tell them of Christmas in the summer in the southern hemisphere. Now go 90 degrees around, show them the (spring) equinox when day and night are equal in length. Ask them when this happens. In fact, the spring equinox is this Friday, March 21. The Earth passes this point on its orbit about 7 pm Thursday night. So days and nights will be about equal everywhere on Earth.
Go around an entire orbit once more, get them to figure what month it is, what season in north and south. Show them arctic and Antarctic circles, if you wish show them tropics, places where Sun gets overhead some day in the year. More importantly, show them how Sun gets higher overhead in summer but tilts farther south in winter (for us – farther north in southern hemisphere).
Phases of the Moon Activity
The idea today is to reinforce the previous discussions of day/night and seasons, and use the ideas we have showed them so far to introduce the phases of the Moon. We will want to arrange the classroom so that the Sun (our naked bulb) can be in the center today.
· Start by reviewing the stuff from previous weeks: remembering how the positions of Sun and Earth determine day and night is useful both for the analogy to how the Moon shines and to understand why we see it at different times. Give them a few minutes to ask questions about past material; stop this before the questions degenerate to complete irrelevance…
· Now start talking about the Moon. Ask them – what does the Moon look like? Summarize the discussion by pointing out it seems to change shape.
· Next question: What is the Moon made of? Ignore the cheese joke and get to rock. So how does a chunk of rock change shape? Summarize – Moon does not change shape but it looks as if it does. Today we’ll figure out how this works.
· Actually, how does a chunk of rock shine so brightly that we can see it? Let them get to the fact that the Sun shines on the Moon, making it look bright in the sky.
· The point: the Moon is a ball of rock, which shines because Sun lights it up. The directions from Sun and Earth to Moon make it seem to change shape in the sky. Remind them how, when Sun shines on Earth, it is light (daytime) on half of Earth, and dark on the other half. So it is on the Moon, Sun can only make one-half shine, the other is dark.