So if distance is about the same, what causes the seasons to change?

Let’s talk about light, dark, and us…

Celestial sphere

Incoming solar radiation

Insolation

All sunlight is the same—it

comes from the same sun to

the same Earth.

But all sunlight does not “hit the Earth” the same way!

Angle of Insolation

Some light strikes with a low angle

Angle of Insolation

Some light strikes with a great angle

Angle of Insolation

Which is the smaller angle of insolation?

Which will make the ground more hot?

Which will make a SHORTER shadow?

In the diagram at left, an observer in New York State “sees” the sun at

three different noon-times during

the course of a year (X, Y, and Z).

When is the sun at the observer’s zenith?

Never!

ZENITH

Which sun has the greatest angle of insolation? Z

The animation indicates a shadow growing to the east, because

(1) the sun is rising in the east.

(2) the Earth rotates the same way.

(3) the sun is setting to the west.

(4) the Mayan calendar ends this year!

How fast does the sun move along its X, Y, or Z path?

15 o/hr

ZENITH

Which sun gives the observer the longest shadow?

X

In the diagram at left, an observer in New York State “sees” the sun at

three different noon-times during

the course of a year (X, Y, and Z).

Which light waves are more concentrated?

Which light waves are more diffuse?

Which has more energy?They are both equal!One is more diffuse and one more concentrated!

Which diagram best shows the noon Sun providing an observer with the greatest amount of insolation?

WHY?

angle of insolation

energy from the sun!

So, why does it change?

Angles of insolation vary for 3 reasons:

1. The season (Angle of insolation is greater in summer)

2. The latitude of the light (The lower the latitude the greater the angle)

3. The time of day (Angle of insolation is greater at noon)

SEASONS

LATITUDE

TIME OF DAY

In New York State, summer is warmer than

winter because in summer New York has

(1) fewer hours of daylight and receives low angle insolation

(2) fewer hours of daylight and receives high angle insolation

(3) more hours of daylight and receives low-angle insolation(4) more hours of daylight and receives high angle insolation

Which graph best represents the general relationship between latitude and average

surface temperature?