Earth in Space

The Solar System

• Consists of:– Sun– 8 planets• Pluto is now considered a Dwarf

– About 90 satellites of the planets, a large number of small bodies (comets and asteroids), and interplanetary medium (the material that fills the solar system).

Planets

• Can you name the 8 planets?

–TURN & TALK• Come up with a way to remember the 8 planets with

your group, be creative!

Orbits

• The orbits of the planets are ellipses with the Sun at the focus.– However, Mercury and Pluto orbit very similar to

the shape of a circle due to their location to the Sun.

Orbits

• Every planet in our solar system except for Venus and Uranus rotates counter-clockwise as seen from above the North Pole– This is the same direction in which all the planets orbit the

sun. • Fun Theories!!

– Uranus was likely hit by a very large planetoid early in its history, causing it to rotate "on its side," 90 degrees away from its orbital motion.

– Venus rotates backwards compared to the other planets, also likely due to an early asteroid hit which disturbed its original rotation.

What is in the Solar System?

• Planets- big bodies orbiting the Sun.• Satellites- another word for moons, which are

variously sized objects that orbit a planet.• Asteroids- small dense objects orbiting the

Sun.• Comets- small, icy objects with highly unusual

orbits.

What is the origin of the Universe?• The Big Bang Theory– About 15 billion years ago a tremendous

explosion started the expansion of the universe.– At the point of this event all of the matter and

energy of space was contained at one point.

Where Are We?

• The Solar System is located in the Milky Way galaxy, a barred spiral galaxy with a diameter of about 100,000 light-years containing about 200 billion stars.

• Our Sun resides in one of the Milky Way's outer spiral arms, known as the Orion Arm or Local Spur.

Fun Facts About the Universe

• It was hot when it was young, and will be cold when it grows older…Similar to food!

• The Universe is 13.7 billion years old.• The Earth is not flat…but the Universe is! • The Universe has no center. In fact, everything is in a hurry to move away from the center of the Universe!

Earth

Gravity

• The force of gravity pulls every object toward every other object.– Depends on its size and its mass

• Earth is so big that its gravity is strong enough to hold onto the gases we need for life.

Earthly Days

• Earth rotates, or spins like a top, one complete turn every 24 hours.– As Earth rotates, it turns towards the east.

• When we are facing the Sun, it is daytime. When we are not facing the Sun, it is night.

• Planets rotate on an imaginary line called an axis.– The two ends are called the North Pole and the

South Pole.

Earth

• Without the pull of the Sun’s gravity, Earth would fly off into space.

• The Sun’s gravity pulls the Earth into its orbit, which is in the shape of an ellipse.

• Earth’s axis is tilted about 23.5 degrees, which gives us summer and winter.

• During the winter, the Sun appears low in the sky and the arc is shorter, making for shorter, cooler days.

• In the summer, the Sun climbs higher in the sky and its arc is longer, causing longer, warmer days.

Fairbanks, Alaska on the Summer Solstice.Sunrise: 2:58 AMSunset: 12:48 AMLength of Day: 22 Hours and 10 Minutes

The Moon

About the Moon

• The only natural satellite of Earth.• The second brightest object, after the Sun.• Has no atmosphere• Is the only object in space to be visited by

humans.

Craters

• Often called “impact craters”• Remains of collisions between an asteroid,

comet, or meteorite and the Moon.• Hit the moon at a wide range of speed, but

average about 12 miles per second.• There are millions of craters on the Moon.• There is no erosion (wind or water) on the

Moon to wear the craters away.

Moon

• First visited by the Soviets in 1959.• The only body in space that samples have

been returned to Earth.

Gravitational Forces

• The forces between the Earth and the Moon have interesting effects.– The most obvious is the tides.

Spring and Neap Tides

• Spring– When the Moon is full or new• Gravitational pull if Moon and Sun are combined

– High tides are very high, low tides are very low.• Neap– When the Moon is in any of the “quarter” phases.• Sun and Moon work at right angles

– Small difference between tides and weak.

Far Side of the Moon Near Side of the Moon

Tidal forces from Earth have slowed down the moon's rotation so that the same side is always

facing the Earth, a phenomenon called tidal locking. The other face, most of which is never visible from

the Earth is therefore called the "far side of the Moon".

Moon

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