Reasons for the Seasons

Subject: ScienceTopic: Astronomy

ASTRONOMY

Astronomy ~ the study of space including:.

1. stars

2. planets

3. other objects

AND their origins

ROTATION

The spinning around a central point or axis.

Causes ~ day & night

Rotates from West to East

1 Rotation = 1 DayEx: Earth rotates in

24 hr.

REVOLUTIONTo travel in a circular path around another object.

1 Revolution = 1 year

ORBIT ~ the path an object takes as it revolves around something.

Earth orbits the sun in 365 ¼ days

Earth’s orbit nearly a perfect circle – a slight ellipse

EARTH’S TILTED AXIS

Tilted at 23.5° angle from the vertical

Axis tilted toward the sun in northern hemisphere during summer.

a. longer periods of daylight

b. physically farthest from sun

(about 152 million km)

EARTH’S TILTED AXIS

Tilted away from sun in northern hemisphere during winter.

a. shorter periods of daylight

b. physically closest to the sun in winter

(about 147 million km)

EARTH’S SEASONS

The Real Reasons for the Seasons

Seasons: Spring, Summer, Autumn & Winter

Both Earth’s tilted axis AND its revolution around the sun cause the seasons.

Distance from the sun is NOT the reason for the seasons.

How Sunlight Strikes the Earth

1. At equator sunlight strikes earth directly. It is usually around 80-88 degrees all year! Difference in temperature from winter to summer is only 1 degree.

2. Closer to the poles sunlight

strikes earth at an angle

a. near poles sunlight spreads out over

larger area

EQUINOXMeans ~ equal nights

a. length of day & night about equal

Noon sun is directly overhead at equator

Earth’s tilt not toward or away from the sun. Zero tilt.

Vernal Equinox ~ spring begins in N. hemisphere

Autumnal Equinox ~ fall begins in N. hemisphere

SOLSTICENoon sun is overhead at

23.5° N (June) 23.5° S (December)

Summer Solstice – longest day (≈ June 21)

1st day of summer

Sun at it’s highest point

Winter Solstice – shortest day (≈ Dec. 21)

1st day of winter

Sun at it’s lowest point

EQUINOX AND SOLSTICE

Interesting Facts

Utah has the greatest number of day light hours in the summer.

The sun’s rays strike the earth the farthest north and the farthest south during the summer and winter solstices.

If you watched the night sky for several hours, the stars would appear to be moving around the North Star, however the stars aren’t moving.