8th Sun-Earth System
Notes 1
A. Star - A huge ball of gas (mostly Hydrogen and helium) held together by gravity.
 The central core of a star is extremely hot and produces energy.
 Some of this energy is released as visible light, which makes the star glow.
B. The Sun -the star around which our earth orbit
 a yellow star of average temperature and size in comparison to other stars
 The Sun's diameter is 864,938 miles (1391980 km) – about 109 times bigger than the Earth.
C. How does the Earth Move?
Earth moves through space in two major ways:
1. Rotation –

Earth’s axis is an imaginary line that goes through the center
of the Earth from the North Pole to the South Pole.

The axis is NOT straight up and down; it is tilted at an angle of 23.5 degrees – the axis ALWAYS points
in the same direction in relation to the sun

The spinning of the Earth on its axis is called
rotation.

Rotation of the earth results in daytime and night

Earth completes one rotation in 24 hours (1 day)
2. Revolution

Revolution is the movement of one object around
another
o One complete revolution of the earth around
the sun takes one year
o Earth follows an orbit - a path a body travels
around another body – as it revolves around the sun

Earth circles the sun in an ellipse – an elongated circle - or elliptical orbit.
D. Lines of latitude and longitude

lines of latitude – imaginary parallel lines running east to west on the globe
o equator - zero degree line of latitude
a) divides the earth into 2 hemispheres – northern and southern

lines of longitude – imaginary parallel lines running north to south on the globe
o prime meridian – zero degree line of longitude
i. runs through Greenwich England
ii. places east of the line are in the Eastern Hemisphere
iii. places west of the line are in the Western Hemisphere
E. What causes seasons?

Seasons are caused by the tilt of the Earth’s axis as Earth revolves around the sun.

The north end of the axis is pointed away from the sun in one part of the year (winter) and pointed toward
the sun in another part of the year (summer)
Seasons in the northern
hemisphere

Why does the northern hemisphere experience summer in June, July and August?
o This is when the northern hemisphere receives the most direct sunlight
o At the same time, the southern hemisphere is tilted away from the sun so it receives mostly indirect light
so this hemisphere experiences winter
Indirect sunlight
Most direct sunlight
Indirect sunlight
Solstices and Equinoxes:
Date
Northern hemisphere
Southern hemisphere
Vernal (spring) equinox
March 21
Both hemispheres experience equal
amounts of sunlight
June 21
Autumnal equinox
Summer solstice:
Winter solstice:
Longest day of the year
Shortest day of the year
N.H. tilted as much towards the sun as
possible
Southern H tilted away from the sun as much as
possible
Autumnal equinox
Sept 22
Both hemispheres experience equal
amounts of sunlight
Vernal equinox
Winter solstice
Summer solstice
N.Pole receives 6 months of darkness
S. pole receives 6 months of day
Dec 21
Copy Notes:
Why do planets stay in orbit around the sun?
Because objects exert a gravitational force on every other object – this force (f) attracts objects toward one another.
1. gravitational force – the amount of pull gravity exerts on an object; on or near the surface of the earth the
gravitational force is equal to your weight (your mass x 9.8 m/s2)
Newton’s Law of Universal Gravitation – - the larger the masses of two objects and the closer together the objects are, the
greater the force of gravity between the objects
The strength of Gravitational F depends on two factors:
1. mass of the objects (mass is the amount of matter in an object)
2. distance between the objects – F of gravity (g) decreases rapidly as distance increases
Question – what would happen if the distance
between the earth and moon decreased? Answer:
The F of gravity between them would increase.
The sun is way more massive than the earth – by a
million times! So, why doesn’t the Earth crash into
the sun? Answer – because of Inertia: the
tendency of an object to resist a change in motion
– the greater an object’s mass the greater its
inertia.
Newton’s 1st Law of motion – an object at rest will stay at rest and object in motion will stay in motion.
Example – a car suddenly stops and you keep moving forward – this is why we wear seatbelts. Your body resists the change
in speed; however it will eventually stop, why? Air resistance and gravity on Earth
Newton concluded that 2 factors hold planets in orbit: inertia and gravity combine to keep earth in orbit around the sun.
- As long as nothing interrupts the earth’s speed and direction it will continue to orbit the sun.
Last Glossary Words:
2.
3.
4.
5.
6.
7.
Heat – the transfer of energy from a hotter object to a cooler one.
Convection – transfer of heat to other places by the movement of liquids or gases
Conduction – direct transfer of heat from one substance to another substance that it is touching
Radiation – EM energy coming directly from the sun
Photon – a single unit of EM radiation; a particle of light
Scattering – when photons of visible light (a form of EM radiation) bounce off particles of dust and gas
molecules in the sky; this causes the sky to be blue during the day
8. Electromagnetic waves (EM) – vibrating electric and magnetic fields that move through space at the speed of
light
9. EM radiation – same as EM waves
10. Gamma rays – highest frequency (thus highest energy) EM radiation; very dangerous to living things
11. Ultraviolet (UV) rays – high energy EM radiation that can damage or kill living cells; causes sunburn
12. Infrared radiation – EM radiation that we feel as heat
Heating the troposphere
Radiation, Conduction and Convection work together to heat the troposphere
Radiation – EM energy directly from the sun warms earth’s surface
Conduction - Conduction helps warm the lowest part of the
atmosphere when cooler air molecules bump into warmer surface
molecules – heat is transferred from the warmer molecules to the
cooler molecules.
Convection - warmer air molecules near the surface of the earth
(that were heated by conduction) move faster than cooler air
molecules above them; warm air rises because it is less dense and
the cooler air sinks towards the surface
Convection of air molecules results in warm air constantly moving
up and cooler air constantly sinking and then being warmed and the
cycle continues.
Most of the heating of the atmosphere is caused by convection
TO DO: Add to your glossary:
13. Temperate zone –zone of the earth between 23.5 degrees latitude and 66.5 degrees latitude, north and
south of the equator
14. Tropical zone – zone of the earth between 23.5 degrees north and 23.5 degrees south of the equator
15. Polar zone – zone of the earth that extends from 66.5 degrees to 90 degrees north and 66.5 degrees to 90
degrees south of the equator
16. Gulf stream – a current of water that brings warm water and warm air from the Gulf of Mexico along the east
coast of the United States to Ireland and southern England – as a result these areas have a mild, wet climate
despite their relatively high latitudes.
17. Altitude/elevation – distance above sea level C
18. Climate – average, year-after-year conditions of temperature, precipitation, winds and clouds in an area.
TO DO: Copy ALL into your notebook - stamped
Climate – average, year-after-year conditions of temperature, precipitation, winds and clouds in an area.
2 main factors are used to describe a region’s climate:
1. Precipitation
2. Temperature
What affects temperature?



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Latitude – general trend that temperatures decrease as latitude increases
Altitude - temperature’s decrease as altitude increases within a temperature zone.
Distance from large bodies of water –land temperatures tend to be less extreme near oceans
Ocean currents – current can bring warm or cool water/air to coastal landmasses resulting in warmer or
cooler temperatures than expected at those latitudes
Temperature
Zone
Latitude
Sun rays angle
temperature
Tropics
23.50 N to 23.50 S
Nearly direct all year long
Warm to hot all year
Temperate
23.50 N to 66.50N
23.50 S to 66.50S
Nearly direct in summer to a low
angle in winter
Warm to hot and cool to
cold depending on the
latitude within the zone
polar
66.50 N to 900N
66.50 S to 900S
Nearly parallel in the summer/almost
Cool to cold all year
non-existent in the winter
Ocean currents – as an example, warm ocean currents moving from the tropics toward the poles bring warm air with it.
Gulf Stream – warm water originating from the warm Gulf of Mexico crosses the North Atlantic bringing mild, humid air to
Ireland and Southern England.
AIR PRESSURE IN EARTH’S ATMOSPHERE:
Composition of the atmosphere from highest to lowest abundance:
Nitrogen
78% of atmospheric gases
oxygen
21% of atmospheric gases; most organisms require oxygen
for cellular respiration
.04% of atmospheric gases; plants MUST have carbon
dioxide to make their own food via photosynthesis
Only very small amounts present
Carbon dioxide
Argon and other
trace gases
Other:
Water vapor
particles
Water in gas form; amount varies from place to place;
condenses to form clouds
tiny solid and liquid particles such as dust, smoke, salt and
other possible pollutants
Air Pressure
Pressure – the force pushing on an area or surface.
Air pressure – the result of the weight of a column of air pushing down on an
area:




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the column of air extends upward through the entire atmosphere
the atmosphere is heavy
Air molecules push in all directions which is why you are not crushed
by the column of air above you.
Amount of air pressure in an area changes frequently
Denser air (more air molecules in a given space) exerts more pressure
than less dense air.
Altitude and Air Pressure
Altitude – the distance above sea level
Air density – the mass of the air divided by the amount of space it is taking up (aka its volume)

Air pressure decreases as altitude increases; as the density of air decrease so does air pressure decrease.

As you increase your altitude, the density of air (# of molecules in a given area) decreases and the distance
between air molecules increases (see diagram).
READ ONLY: Think of air pressure as a column of books – the book on the bottom has the weight of all the other books
pressing on it and the book at the top has the least pressure; in a column of air, the air at the bottom has all of the weight
of the air above it so this is why air pressure is greatest at sea level (remember that the gravitational force of the Earth is
pulling on air molecules just like it is pulling on a book, but the strength of the force is much less since air molecules have
very little mass).
How Earth’s Atmosphere is Heated:
Nearly all E in the atmosphere comes from the sun
E travels to the Earth as Electromagnetic (EM) Radiation from the sun
Only 3 forms of EM radiation pass through Earth’s Atmosphere:
1. Visible light
2. Infrared radiation
Light humans can see
3. UV light
High energy radiation
We feel it as heat
Causes sunburn and cancer
Electromagnetic Radiation has 3 synonyms that all refer to the energy emitted by the sun:
1. Electromagnetic waves
2. Light energy or just light
3. Photons - a single unit of EM radiation; a particle of light
The ozone layer in the stratosphere absorbs the highest energy EM radiation – x-rays and gamma rays - that would kill living
things if it reached earth’s surface

inertia – an object’s resistance to changing its speed or direction until an outside force acts on the object

troposphere - lowest portion of Earth's atmosphere; holds approximately 80% of the atmosphere’s mass
and where Earth’s weather occurs

stratosphere – layer of the atmosphere extending from the top of the troposphere to 50 km above
earth’s surface

Ozone layer – a layer of ozone gas found in the stratosphere; occurs about 8 to 30 miles (12 to 48 km)
above the earth; ozone layer converts some solar EM radiation into infrared radiation (heat) and blocks
most of the UV radiation from entering the troposphere.

ozone - an oxygen molecule that contains 3 oxygen atoms instead of the usual 2 atoms (the type we
breathe)

Greenhouse effect – a natural process by which atmospheric gases hold heat in the air

Greenhouse gases – gases (water vapor, carbon dioxide and methane )that absorb EM radiation and emit
it back into the atmosphere as heat