Hi. It's Paul Andersen and this is disciplinary core idea ESS1B. It's on the
earth and the solar system. The solar system is not only the sun and the earth but it's
everything that orbits around the sun. So it's going to be all the planets from Mercury
to Neptune. It's going to be the dwarf planets like Pluto. It's going to be the moons around
those planets. It's going to be asteroids. It's going to be everything that orbits around
the sun. Why is everything orbiting around the sun? It's because of the huge amount of
gravity or gravitational force of the sun. And that gravity led to the formation of the
solar system as well. So we think it used to be just a massive disc made up of dust.
And gravity pulled those dust particles together. They became bigger and bigger and bigger.
Eventually formed the sun at the center and the planets around that. And they're still
in orbit around the sun. Now we used to think that the earth was at the center of the solar
system. But a number of scientists, like Galileo, Tycho Brahe and Kepler allowed us to understand
what's really going on. And Kepler's laws explain how the solar system works. He basically
had three laws. The first one is that the orbits of planets around the sun are elliptical.
And the second law is kind of drawn right here. The idea is that in a given period of
time the objects are going to move and sweep out an equal area over time. And so when you're
closer, so a planet is going to kind of move around the sun like this, as it gets closer
to the sun, it's actually going to go faster and it's going to go slower when it's further
away. Another scientist, Sir Isaac Newton used the work of Kepler to come up with a
better model of what's going on in the solar system. And predicting the motions of object
in the sky. And so what are some things that we can use this current model to predict?
We can use it to predict how the planets might move through the sky. And so everything that
you see in the night sky is not necessarily a star. It could be a planet. And these planets
show something called retrograde motion. So they'll move backwards almost in the night
sky. Why is that? It's because we're either passing them or they're passing us. And you
can figure out other things. Like Venus, which is inside of us, we tend to only see it in
the morning and at night and that's because we're only going to see that because it's
on the inside of our orbit. We can understand how eclipses work. This is a lunar eclipse.
And why we go through phases. So why does the moon go through phases in the course of
a month? We can understand all of those using this simple model that was developed by scientists.
Now everything isn't static and doesn't continue like that forever. In fact even the earth,
as it spins, is gradually slowing down over time. The earth is not straight up and down
in relation to the sun. It's slightly tilted. And that tilt changes over time. And so if
we look at, this is measuring from today and thousands of years in the past and in the
future, that angle is actually going to tilt. It's going to wobble. And these ellipses are
going to vary over time. And so all of these variations can lead to changes over time.
And so the ice ages are actually caused by changes in not only the orbit of the earth
but its tilt as well. And you can see those over time. This model allows us to understand
how the seasons work. And so if that axis, if I were to draw it right here, sometimes
the axis is kind of tilted towards the sun. And that would be during the time of summer.
And sometimes it's tilted away, like in winter. And so in our winter in the northern hemisphere,
we're actually closer to the sun the sun than we are during the summer. But since we're
tilted towards the sun in the summer, we're going to get more direct light. And that's
why our summer is going to be winter in the southern hemisphere. And so how do you teach
all of this to our students? Well at the beginning, in the early elementary grades, you want them
observing. And you want them making descriptions and finally making predictions. And so a great
way to start doing this and understanding how the earth moves in the solar system is
just looking at sunset and sunrise. So what time is the sun rising? And what time is it
setting? And so you could keep track of that during the year. And what you would get is
a pattern that looks like this. And so what's happening? Well, during the summer months,
like June and July, it's actually, the sun is setting later during the day and it's rising
earlier. And that might make sense. And so we can see patterns during the year. What
are these little jagged points? Those are going to be daylight savings. And so you could
talk about that as well. As we move into the upper elementary grades we want to start talking
about this model and what all of these motions are actually causing. And so the motions of
the earth around the sun and the moon around us is going to cause night and day. As the
earth spins, if we're facing the sun we're going to have day. And as we're moving away
from it we're going to have night. And that takes about 24 hours. It's going to explain
why we have seasons. So during the summer we're tilted towards the sun. During winter
we're pointed away. And it's also going to explain phases. And so the moon is going to
go through phases during the month. And so to explain that I would have to make a whole
separate video. But you could have your students start collecting data on the phases of the
moon. And then using models like this to kind of walk students through the phases. You also
want to talk about the stars and how they move. The stars will actually orbit during
night time. We can't see that unless we do some time lapse. And the star right in the
middle, the North Star, won't really change. And so the stars aren't moving, it's that
the earth is spinning so the stars seem to change. And you can talk about constellations.
Or simply patterns of stars in the night sky that we're visualizing, even though these
stars might not be close to each other at all. As you move into middle school you want
to talk more about the solar system itself. All the parts of the solar system. Not only
the planets but the dwarf planets, moons, asteroids. As we move into middle school we
want to get more precise into some other phenomena that are caused by these motions. And so this
motion causes tides. And so sometimes the water is going to go out. And sometimes it's
going to come in. And that's due to gravitational forces between the moon and the earth. And
why we have eclipses. So why do we get a lunar eclipse like this? That's where the earth's
shadow is actually cast on the moon. So the light from the sun isn't making it from the
moon. And so the moon would have to be over here. And why we might have a solar eclipse.
When the moon is on this side and is blocking out the light from the sun. And why don't
we have these you know once a month? That's because everything is at a tilt. And so they're
really, really rare. It's also going to understand planetary motions. And so why do sometimes
planets backwards in the night sky and sometimes move forwards? And so we really have to have
models like this to understand it. We also want to talk about seasons in middle school.
Why we go through seasons. And how long does it take for the earth to move around the sun?
It's going to take one year. And that's why we're going to have these seasonal changes.
As we move into high school then we start getting into more specifics of the model.
It would be okay to talk about Isaac Newton's ideas of gravitation. And Kepler's laws of
motion. We can talk about ellipses and the speed of planets throughout that time. We
should also talk about that everything is not static. That we're going to have changes.
Changes in the wobble of the earth. Changes in the eccentricity of these orbits around
the sun. And those can eventually lead to patterns, like the ice ages over time. And
so that's the solar system. And I hope that was helpful.