The Solar system is made up of:

• The sun:
• The sun is a sphere of hot, burning gas that provides heat and light to the planets.
• The planets:
• Orbit (go round) the sun; they are made of rock and gasses.
• The orbits of the planets are ellipses (slightly oval).
• The orbit of Pluto is highly elliptical; sometimes it is closer to the sun than Neptune.
• Many of the planets have moons:
• These are rocky spheres that orbit the planets.
• The planets in order out from the sun are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto.
• The planets all orbit the sun in more or less the same plane – the ecliptic.

• The further away from the sun a planet is the less heat and light it receives from the sun:
• Therefore the further from the sun the colder the planet is.
• Between objects there is nothing – no air:
• We call this a vacuum.
• The vacuum of space makes manned exploration difficult (see below).

Gravity

The attractive force of gravity affects everything in the universe:

• Gravity is a pulling force all objects exert on each other:
• Gravity is a very weak force.
• The more massive an object, the bigger the pull of gravity:
• Only very massive objects have a gravity that we can feel.
• The further objects are apart the lower the force of gravity between them.
• Because the planets and moons have different masses the force of gravity on them is different:
• An object’s mass is a property of an object and doesn’t change.
• An object’s weight is the forge of gravity acting on its mass.
• On the moon you would weigh ¹/₆ of your earth weight.


• Astronauts in the space shuttle seem to be weightless even though they are close to the earth:
• The gravity of the earth is pulling them towards the earth
• However they are travelling very fast in a circular orbit.
• Imagine an experiment with a big cannon.
• The faster the shell is fired the longer it takes to fall to earth.

• Imagine now a very, very powerful cannon
• Eventually if the shell is going fast enough, as it falls to earth the earth curves away from it.; It will never hit the ground.
• Anyone in it will appear weightless since they are falling freely too.
• This is the effect that causes to astronauts to seem weightless.

Times and Units

The orbit of the earth and its tilt gives us days, months, seasons and years:

• The Earth turns on its axis once every 24 hours giving us a day.
• The earth orbits the sun once every 365¼ days giving us a year.
• The earth is tilted on its axis; that causes the seasons because one hemisphere gets more energy from the sun.

• The moon orbits the Earth every 28 days giving us a lunar month.

• The 28-day orbit of the moon round the earth causes the phases of the moon:
• When you stand on the earth and look at the moon the sun appears to illuminate different areas of the surface.

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• The new moon is when the moon is just appearing at position B.
• The full moon is at position E.
• The old moon is at position H.
• As a matter of interest, you don’t need to learn this, but the moon in positions D and F is called gibbous!

Sizes of objects:

• The planets range in size:
• From Pluto at 3,000 kilometres across.
• To Jupiter at 140,000 kilometres.
• The sun is a small to middle sized star:
• The diameter of the Sun is 1,400,000 kilometres (10 times that of Jupiter).
• Millions of stars cluster together into a spiral to make up our galaxy:
• The galaxy is 1 million, million, million km across (1 trillion km).
• All the galaxies and the space between them together make the universe:
• This is unimaginably vast.

Exploration

Space can be explored in three ways:

• Telescopes:
• The advantages of using telescopes are:
• You can see for great distances into the universe.
• They are relatively cheap to build.
• There is little danger to humans in using them.
• The disadvantages of using telescopes are:
• You can’t get close up to the objects you are studying.
• The atmosphere blurs the details of the objects.
• Unmanned space vehicles:
• The advantages of using unmanned space vehicles are:
• You can get to objects.
• You can study the objects closely.
• They are still relatively inexpensive.
• There is little danger to humans in using them.
• The disadvantages of using unmanned space vehicles are:
• They cannot react to unexpected events.
• The speed of light means there is a delay in controlling them.
• If they break down they cannot be repaired.
• Manned space vehicles:
• The advantages of using manned space vehicles are:
• You can get to objects.
• You can study the objects closely.
• Humans can react well to the unexpected.
• Humans can carry out repairs.
• Humans like exploring.
• The disadvantages of using manned space vehicles are:
• You have to carry air and food.
• You need a lot of power to move the vehicle and keep the humans warm.
• You need space to live.
• They are very expensive.
• There is danger to humans in using them.

Theories about the universe.

• The Big Bang theory:
• This theory suggests that the universes began in a huge explosion something more than 10 billion years ago.
• Since then the universe has been expanding.
• The universe will end in either a cold waste or possibly in a “big crunch” depending on a factor we cannot measure accurately enough at the moment (its total mass).


• The Steady State theory.
• This theory suggests that matter is constantly being created in the universe.;
• The universe is expanding because of this.
• There is no beginning or end of the universe since fresh material is always available for new stars to form.
• The balance of scientific opinion would suggest that the “Big Bang” theory is the correct one.
• ;

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Solar Eclipse:

• A solar eclipse occurs when the moon comes between the sun and the earth
• Under the shadow of the moon it is dark

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