Without the Sun: Episode 2-The Earth-Sun Relationship


Uploaded by geoscienceEIU on 17.10.2011

Transcript:
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To understand how weather functions
and the climate functions over time, we
must understand the earth sun relationship.
The earth-sun relationship is vital to this whole process,
without the sun there is no weather fun.
So in order to understand, let's go ahead and look at the earth
and the sun together from a distance.
And draw with me, we have the sun, we have the earth at this
position at one time of year, and then we've got this other
earth, another position of the earth at another time of year.
So we have this eliptical orbit around the sun, it is eliptical
and one point during the year we are closer to the sun than the
other part of the year.
Now contrary to what you might know that the earth is closer to
the sun in winter, this is true.
On the opposite side of this we are further away
from the sun in summer.
Alright so let's talk about the position
that's closest to the sun.
At this point we're dealing with the term called Perhelion.
Perhelion means closer.
Closer to the sun.
And it occurs on January 1.
So the earth is closer to the sun, now you're probably
thinking, "Well it's not hot during this time of year."
Well you're right, but it is warmer in the southern
hemisphere because the southern hemisphere, I'm going to draw
this line to be the equator, the sun is now closer to the
southern hemisphere, the southern hemisphere is closer to
the sun because of the tilt.
The northern hemisphere is cold because we're tilted away from
the sun, the northern hemisphere is away from the sun.
So at this point we have Perihelion,
which occurs on January 1st.
Let's switch onto the opposite side of the year, this distance
is called Aphelion, this point in earth's orbit is called
Aphelion and it occurs on July 1.
Now these dates, these are just averages, these are just
particular points in time, they do fluctuate, sometimes
Perihelion will be on January 3rd, or December 31st, or
December 30th, and likewise with July, July 4th, maybe July 3rd,
maybe June 30th, etc. And so we've got two points in the year
where we are closer to the sun, and we are further from the sun.
Now let me just point out again, this is our winter, the northern
hemisphere's winter, and the tilt is
the reason why it's colder.
Even though we are closer to the sun, the tilt of the earth
causes us to have less radiation at the surface.
And this is our summer.
So at this point this is the earth-sun relationship dealing
with distance from the sun.
Now another point is that sometimes we think that the axis
shifts, well it does, over time it does shift.
But I wanted to bring up another term and it's called Axial
Parallelism, Axial Parallelism.
Axial Parallelism, if you take that, the axis is parallel
throughout the entire year.
So if we were to draw several axis' throughout the year on
this orbit, they would all point in the same direction.
So here is 23.5 degrees tilt, etc.,
that's throughout the year.
So the axis points in the same direction throughout the year,
throughout the year, the earth's axis is like this.
It is not like this, where if I'm the sun we're not dealing
with an axis that's like this that's pointing, the northern
hemisphere is pointed away from the sun all year, if that were
the case it would be cold in the northern hemisphere all year
round, there would be no summer.
So Axial Parallelism gives us, one it's giving us a tilt, two
it's pointed in the same direction which allows a change
in season.
So we have two differing seasons and then we have two similar
seasons, the spring and the fall.
So at this point, we have the Winter Solstice and this is the
Summer Solstice.
So if you look here, the northern hemisphere is now
closer to the sun, it's pointed toward the sun
so it is our summer.
Vice versa here in the southern hemisphere, the southern
hemisphere is closer to the sun so it
is their summer and our winter.
So keep in mind that we're talking about differences and
we're talking about opposites, these are opposites, whatever
happens in the southern hemisphere, is the opposite of
the northern hemisphere.
Alright, now let's bring in our seasons, the reason for the
seasons is the tilt of the earth, the tilt of the earth.
So we get four different times of the year, and those
climatalogical seasons occur at four different times, so this,
we'll go ahead and put this in there, and this
is the Winter Solstice.
Here is the Summer Solstice over here.
And solstice means "to change."
We'll leave these two here and we'll just
talk about the two dates.
Winter Solstice occurs on December, and this is a range,
we're going to do 20-23rd, 20-23rd.
And then if we go to the Summer Solstice, Summer Solstice begins
in June, June 20th-23rd.
Now it's not in particular in one year you're going to have
December 21st is when Winter Solstice occurs.
We'll go with this orbit here, earth's orbit.
Now we'll draw in two more points of the earth's year, and
this is going to be Vernal Equinox, and this is the
Autumnal Equinox.
Let's take this word apart, this equinox, equ-nox, in Latin this
means "Equal nights."
It is the spring equal nights.
Equinox, no matter where you are on the earth, you're going to
have 12 hours of day and 12 hours of night.
It doesn't matter how you slice it, wherever you're at,
Timbuctu, Egypt, or Siberia, you're going to have 12 and 12.
At the North Pole and at the South Pole, both are going to
have 12 hours of day and 12 hours of night.
So that's Vernal Equinox, and then we have Autumnal Equinox,
now I'm going to go ahead and shade in this area because on
this side of the earth this is in darkness and this is shaded
in as well, darkness on the outside because the sun is the
source of light.
And if you notice here, when I shaded these in, you get 12 and
12, 12 and 12.
Here you get 24 hours of darkness.
Here's 24 hours of light, and then you get here it's 24 hours
at the North Pole, 24 hours of daylight and 24 hours of
darkness at the South Pole.
Now let me bring you back to this I'm
getting ahead of myself.
The Autumnal Equinox occurs between September 20th-23rd, and
then the Vernal Equinox occurs between March 20th-23rd.
So we have four points in the year which is referred to as our
climatalogical season.
We have a season that begins in September that begins on
September 20th-23rd and it is the equinox,
the Autumnal Equinox.
Then we shift and go further into the year, the end of the
year, December 20th-23rd, that begins our Winter Solstice, we
continue to travel into the dead of winter and then we get to our
spring, the first day of spring occurs between March 20th-23rd
and then we continue on into summer and then we get our
Summer Solstice is June 20th-23rd.
So these are the four positions around the sun and the four
dates that we get the climatalogical seasons.
So keeping in mind that these, when we go back to school,
that's fall, not necessarily, it's not fall, official fall
begins September 20th-23rd.
So those are the seasons, now I'm going to draw a little
differently so that you can see a chart view or a map view or a
birds eye view of the earth's orbit of the sun.
Here's the sun, go ahead and draw with me, here's the sun,
and then earth's elliptical orbit.
Here's one, two, three, four points in the year that the
earth begins the different seasons.
And I'm going to put a little circle here to indicate the
North Pole, a little circle there that indicates the North
Pole, here's the North Pole, here's the North pole in this
earth, and here's the North Pole here.
And go ahead and let's shade in where the darkness will occur,
so we've got darkness here on this side of the earth, and
we're shading this in.
And then we're shading this in because it's away from the sun,
the light source, you still have the North Pole
indicated by the circle.
And then we have the shading on this side of the earth, still
the North Pole indicated, and then on this side of the earth
here, because it's away from the light source.
So here we have four points we have shaded in, we're looking at
an arial view of the earth and earth's orbit of the sun and
let's go ahead and label the particular points in the year.
So we'll start with this, this is Winter Solstice, because the
North Pole is now in darkness, it is 24 hours of darkness and
that occurs about give or take three months that it experiences
24 hour darkness.
We continue around here and we get the Vernal Equinox, the
equal nights of spring, and that occurs again on March 20-23rd.
And then down here we get the Summer Solstice, and that occurs
on June 20-23rd, and then we end up here in the Autumnal Equinox,
equal nights of fall, and that occurs between
the 20th-23rd of September.
So again we have Winter Solstice December 20th-23rd, we have
Vernal Equinox, again look here see the shading, the shading
it's half and half, half of the North Pole is getting darkness
and the other half is getting light.
That doesn't mean that only this half gets, it's spinning, it's
rotating on the axis.
Rotation occurs 24 hours a day and
so we're constantly rotating.
So everywhere on earth it gets 12 hours
of day and 12 hours of darkness.
Vernal Equinox March 20th-23rd, Summer Solstice is June
20th-23rd, and again when I say through, I'm referring to that
it's a range, equinox or solstice is one particular day.
So, and then we continue around, and I'm going to bring back this
Summer Solstice the daylight, the North Pole is in the
daylight, and that the North Pole gets 24 hours of daylight
for two to three months of the summer because the North Pole is
then pointed toward the sun at this time of year.
And then we continue on our way, the Autumnal Equinox is on
September 20th or 21st, 22nd, 23rd, and then we begin again
with Winter Solstice.
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