Solar System

8th Grade(adapted by Mrs. Hubbard)

What causes Day / Night?

Earth’s rotation (spin)• Earth rotates on its axis (imaginary line

through the north and south poles).• It takes about 24 hours to make one

complete rotation.• At any one time, half the Earth is

illuminated by the Sun.

Flat Earth vs. Spherical Earth

SUN

SUN

Flat Earth

Sphere

If Earth were flat, at noon all the sun’s energy would hit the surface at the same angle.

Since Earth is a sphere, the Sun’s energy hits the surface at different angles…causing differential heating

Direct vs. Indirect Sunlight

Because of Earth’s spherical shape, the light that reaches from the Sun hits at angles. These angles of light are known as either: Direct or Indirect sunlight.

Indirect = more spread = less intense energy

Direct = concentrated = more intense energy

If Earth had NO Inclination (tilt)If Earth had NO tilt, then there would be no seasons throughout the year & each day would be an equinox (12 hours of light & 12 hours of night)

Earth’s Inclination (tilt)Earth IS tilted (inclined) which helps cause the seasons and different amounts of day and night throughout the year.

23.5º inclinationATMOSPHERE

Earth’s RevolutionEarth revolves (orbits) around the Sun once every 365 ¼ days = 1 year. Every 4th year a day is added…LEAP YEAR.

Elliptical orbit (oval)

Winter

Spring

Summer

Autumn

What Causes SeasonsCombination of Earth’s tilt (differential heating of surface) & revolution (orbit) around the Sun causes seasons.

NOT DISTANCE FROM SUN!!

Northern hemisphere tilted toward the Sun = more Direct Sunlight = Summer

Northern hemisphere tilted away from Sun = Indirect Sunlight = Winter

How does the moon stay with Earth?

Earth’s gravity pull is greater than the Moon’s and has trapped it for billions of years!!

• Earth pulls on the moon more than the moon pulls on Earth. (Earth is more massive = greater gravity).

Moon is ¼ the size of Earth.

What if…– If moon was not moving, Earth’s

gravity would pull it in!

If Earth did not have gravity, the moon would fly out into space! (Law of Inertia)

EARTH

MOON

What is the Law of Inertia?• This is Newton’s 1st Law of Motion. • Law of Inertia states:

1. An object in motion will stay in that same motion (direction & speed) until change is caused by an outside force.

2. If an object is at rest, it will remain at rest until an outside force acts upon it…puts it in motion.

Centrifugal Motion• Since the Earth’s gravity is present,

and the moon is in motion (tries to go straight, but can’t), it starts a circular path around Earth (orbit / revolution).

• This revolution around Earth causes an outward pull (Centrifugal Motion) which counters the inward pull of gravity.

Cont…• This constant inward pull from

gravity, along with the constant outward pull by the moon’s centrifugal motion eventually reached a point of equilibrium some 4.5 billion years ago…ever since, the moon has been our closest neighbor!

Our Moon• Earth’s moon is its only natural

satellite• It is about ¼ the size of Earth.• It’s average distance from Earth is

about 230,000 miles (if you were traveling 60 mph in a car from Earth to the Moon, it would take about 5 months!!)

• The moon does NOT generate its own light…the Sun’s light reflects off of it.

Moon’s Motion• Rotation – The Moon spins on its axis

once every 27.3 days (1 day = 27.3 Earth days)

• Revolution – The Moon goes around the Earth every 27.3 days (1 year = 27.3 Earth days)

• Full Moon to Full Moon = 29.5 days…?

Why we get Phases of the Moon.

• From space, half the moon is always illuminated by the Sun. –The moon is a sphere, so the light

coming from the Sun can only illuminate half of it at one time.

• From Earth, we see shadows (phases) because of the angles between the positions of the Sun, Moon, and Earth.

Moon Phases Diagram

SUN

What we see from Earth

View from space

Eclipses of the Moon• The Moon revolves (orbits)

Earth once every 27.3 days. Its path around Earth is not on a straight, even plane.

• Once in a while, the moon will pass directly in front or behind the Earth!–Solar Eclipse–Lunar Eclipse

Moon’s orbitalpath is slanted.

Solar Eclipse• When the moon passes directly in

between the Earth & Sun. The moon casts a shadow on parts of Earth.

Sun notto scale

Lunar Eclipse• When the moon passes directly

behind the Earth and the Earth is blocking the Sun’s light from reflecting off the moon.

Pictures • Solar Eclipse:

• Lunar Eclipse

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Moon & Tides• The Moon does pull Earth some with

its own gravity. Its pull is less than Earth’s so it does NOT affect the solid surface…but it does affect Earth’s oceans.

What are tides?• Tides are the rise & fall of sea

level near a coastline. Since Earth rotates so fast we experience four tides everywhere per day! –2 High Tides–2 Low Tides

Spring & Neap tides • Neap Tide

• Spring Tide

Occur during the 1st & 3rd quarter moons

Occur during the New and Full moons

Difference b/w high & low tides are small.

Difference b/w high & low tides are greater.

Moon & Earth’s Rotation• The dynamics between the Earth’s

waters and the Moon’s gravity pull slows Earth’s rotation.

Seasons on Earth• Earth revolves (orbits) the Sun avg. speed of 70,000mph.

• 1 orbit takes about 365 ¼ days.• Earth’s orbit is not a circle, it is

elliptical (oval).– Elliptical orbit causes Earth’s distance from

Sun to vary.• Aphelion• Perihelion

Tilt of Earthcauses seasons!!!Not distance from Sun.

Direct vs. Indirect Sunlight

Sunlight’s path through ourAtmosphere

• Because Earth is curved and tilted, this causes sunlight to pass through varying amounts of Earth’s atmosphere.

Causes of Seasons on Earth (recap)• Earth is tilted on its axis at 23.5 degrees. As Earth

revolves around the Sun, different parts of Earth receive varying sunlight intensity.– Direct sunlight – Sunlight/heat is more concentrated on an

area of land – more intense – warmer climate.– Indirect sunlight – Sunlight/heat is more spread out, has to

distribute energy to more land – less intense – cooler climate

• Earth is curved (sphere)– This causes sunlight/energy to pass through different

thicknesses of atmosphere• The more atmosphere light has to pass through, the less intense it

is = cooler weather (climate)• The less atmosphere light has to pass through, the more intense it

is, = warmer weather (climate)