Our Corner of the Universe
100 mil ly
5 mil ly
Our Neighborhood
Earth’s rotation, orbit and the
seasons

Only 50% of the
Earth’s surface can
be “lit” by the sun

Because the Earth’s
axis is tilted the area
covered by this 50%
varies throughout the
year
Most important variables
 Earth’s
orbit is 365.25 days long
 Earth’s
axis of rotation tilts 23.5° from the
perpendicular

These two variables account for the seasonal
changes in weather patterns that we observe
in a given year
We have four seasons: why?
The Earth’s axis of
rotation is tilted at
23.5° from the
perpendicular
Earth-Sun Relations
Latitude
 Affects
the amount of insolation received
at the Earth’s surface
 The subsolar point (at right angles to the
plane of the ecliptic) receives most
insolation

Insolation decreases north and south of this
point
 The
subsolar point migrates from 23.5°N
in the summer to 23.5°S in the winter
Subsolar point
The latitudinal zones
Perihelion vs Aphelion
MILANKOVITCH CYCLES
-
ACCOUNTS
FOR
PERIODIC
GLACIATION
OF EARTH
MILANKOVITCH CYCLES
MILANKOVITCH CYCLES
THE NEXT
ICE AGE?
WHEN