Space ScienceSpace Science

Chapter 2Chapter 2

Earth, Moon, and SunEarth, Moon, and Sun

Earth’s rotation causes day and Earth’s rotation causes day and night.night.

Earth rotates once every ____ hours.Earth rotates once every ____ hours.

Earth rotates on a tilted axis and orbits the SunEarth rotates on a tilted axis and orbits the Sun..

Earth’s rotation in sunlight causes day and night.

The changing angles of sunlight on Earth cause seasons.

Space CyclesSpace Cycles

SeasonsSeasons

SeasonsSeasons

A regular change in temperature that A regular change in temperature that repeats itself every yearrepeats itself every year

Axis of rotationAxis of rotation - - imaginary line imaginary line around which around which Earth spins, Earth spins, causing day and causing day and night, and that is night, and that is drawn from the drawn from the north geographic north geographic pole through pole through Earth to the south Earth to the south geographic polegeographic pole

http://vortex.plymouth.edu/sun/axis.gif

RotationRotation - - spinning of Earth spinning of Earth on its axis, which on its axis, which causes day and causes day and night; it takes 24 night; it takes 24 hours for Earth hours for Earth to complete one to complete one

rotationrotationhttp://vortex.plymouth.edu/sun/rot8_an.gif

RevolutionRevolution - the motion of Earth around - the motion of Earth around the Sun, which takes about 365 1/4 the Sun, which takes about 365 1/4

days, or one year, to complete days, or one year, to complete

http://www.usoe.k12.ut.us

Orbit Orbit - curved (elliptical) path followed - curved (elliptical) path followed by Earth as it moves around the Sunby Earth as it moves around the Sun

http://www.vt-2004.org/mt-2003/mt-mercury-orbit.jpg

equinoxequinoxIn an orbit, a position and time in which sunlight shines equally on the Northern Hemisphere and the Southern Hemisphere; a time of year when daylight and darkness are nearly equal for most of Earth.

solsticesolsticeIn an orbit, a position and time during which one hemisphere gets its maximum area of sunlight, while the other hemisphere gets its minimum amount; the time of year when days are either longest or shortest, and the angle of sunlight reaches its maximum or minimum.

The Earth’s TiltThe Earth’s Tilt

The Earth's axis is tilted by 23.45° The Earth's axis is tilted by 23.45°

http://www.crh.noaa.gov/fsd/astro/season.htm

As the Earth moves around the As the Earth moves around the Sun, this axis stays always Sun, this axis stays always

pointing in the same direction.pointing in the same direction.

This means that, during part of This means that, during part of the year, the northern part of the year, the northern part of

the Earth will lean more the Earth will lean more directly to the sun, and during directly to the sun, and during

other parts of the year the other parts of the year the southern part of the Earth will.southern part of the Earth will.

When the northern hemisphere is When the northern hemisphere is leaning away from the sun, the rays leaning away from the sun, the rays

coming from it hit this part of the coming from it hit this part of the Earth at a smaller angle than on Earth at a smaller angle than on

other parts of the world.other parts of the world.

The energy that hits the Earth by the Sun changes The energy that hits the Earth by the Sun changes over of the year.  over of the year. 

The The angleangle the Sun is above the horizon the Sun is above the horizon determines how much heat and light strike each determines how much heat and light strike each

square meter of ground. square meter of ground.

http://inkido.indiana.edu/a100/celestialsphere5.html

In the winter the Sun's energy is weakened In the winter the Sun's energy is weakened because the Sun's ray strike the ground rather because the Sun's ray strike the ground rather indirectly as compared to the summer months indirectly as compared to the summer months when the Sun's rays strike the ground more when the Sun's rays strike the ground more

directly. directly.

http://inkido.indiana.edu/a100/celestialsphere5.html

This means that the ground receives This means that the ground receives more energy (more heat) per square more energy (more heat) per square

meter in the summer than in the meter in the summer than in the winter.  winter. 

More energy is received by the ground More energy is received by the ground during the summer (high during the summer (high

temperatures) and less energy during temperatures) and less energy during the winter (lower temperatures).the winter (lower temperatures).

http://inkido.indiana.edu/a100/celestialsphere5.html

So, seasons are caused the So, seasons are caused the tilt of the Earth’s axistilt of the Earth’s axis

Big

Science

Idea

Remember:Remember:

The seasons are the result of this The seasons are the result of this tilt of the Earth's axis. tilt of the Earth's axis.

If the tilt of the Earth's axis was 0° If the tilt of the Earth's axis was 0° there would be no difference in there would be no difference in how the rays from the sun hit its how the rays from the sun hit its different regions, and there would different regions, and there would be no seasons.be no seasons.

The Earth's seasons are not The Earth's seasons are not caused by the differences in the caused by the differences in the

distance from the Sun throughout distance from the Sun throughout the year.the year.

The seasons are the result of The seasons are the result of the tilt of the Earth's axis.the tilt of the Earth's axis.

I know this is a repeat, but it is important that you understand this idea. Many

Americans, including Harvard graduates, do not know what causes seasons!

http://www.nmm.ac.uk/uploads/gif/seasons-full.gif