2.1 Space ExplorationThe Universe

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Cosmic Definitions N4

There are many different bodies moving around in the universe. Below is a list of some of them with a definition of what they are:

Star A hot ball of matter which is undergoing nuclear fusion emitting light. The sun is an example of a star.

Planet A spherical ball of rock and / or gas which orbits a star. Earth is an example of a planet.

Moon A lump of matter which orbits a planet. Our moon orbits Earth. Deimos which orbits Mars is another example of a moon.

Solar System A solar system consists of a star and all the objects orbiting it as well as all the material in that system. Our Solar System includes the Sun together with the eight planets and their moons as well as all other celestial bodies that orbit the sun.

Galaxy A large cluster of stars, some of which have planets orbiting them.The Milky Way is an example of a galaxy.

Exo Planet A planet outside our Solar System. (or Extrasolar In 2009, there were between 220 and 350 reported exo planets Planet) depending on the criteria used by the counting organisation.

The Universe Consists of many Galaxies separated by empty space.

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What We Have Learned by Heading into Space? N4 N5

Read any debate about space exploration, and this question will invariably come up.

“Why should we be spending money exploring space when there are so many problems here on Earth that we need to solve first?” It’s a tricky one.

One answer is that reaching for new heights often creates new solutions, new opportunities and elevates hope back on the ground.

We have learned so much about our own planet and the expanding universe by exploring space. If mankind had not explored space and used telescopes then we would not have found out the following about:

The Earth A greater understanding about the rotation of the Earth, the orbit of the Earth

around the Sun and how this affects time on earth. e.g. one rotation of the Earth is one day, one orbit of the Sun by the Earth is one year etc.

It has allowed meteorologists to predict and monitor of the weather. Satellites have been put into orbit to monitor the Earth’s weather systems and allows us to predict natural disasters e.g. tsunamis and hurricanes

Allowed the monitoring of the polar ice caps and enabled a plan to be put in place to minimise their erosion and prepare for the consequences of the erosion i.e. rising water levels and the destruction of natural habitats for polar animals.

The Universe Greater understanding of the origin of the Universe The Universe is still expanding Estimate the age of the universe

Through exploration our understanding of the Universe has changed. There were a few misconceptions before our understanding shaped our belief of the expanding universe and the model of it we have today. Scientists at certain times thought:

The Earth was thought to be flat - it's round. The Earth was thought to be the centre of the Universe (see diagram below) - it's

not. The Sun was thought to be the centre of the Universe - it's not. The Milky Way was thought to be the centre of the Universe - It's not. The centre of the Universe was thought to have a definite location - it doesn't.

Satellites

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Evidence to Support our Understanding of the Universe N5

From an earlier section titled ‘The Big Bang Theory’, it is stated that Physicists thought that at one second old, stable particles called protons and neutrons started to form. These particles form our model of the nucleus of the atom. However, something was missing from that model called the Higgs Boson. Professor Higgs, a British physicist wrote in 1969 that the Higgs Boson's role is to give the particles that make up atoms their mass. Without this mass, they would zip around the cosmos, unable to bind together to form the atoms that make stars and planets – and people.On 4th July 2012, Physicists working at CERN at the world’s largest particle accelerator – The Large Hadron Collider – announced the discovery of the Higgs Boson – further evidence to support our understanding of the universe.Some Physicists relate this finding to other landmarks in Scientific history e.g. Neil Armstrong walking on the moon.

Satellites - Introduction N4

A satellite is an object which orbits another object.The Moon is a natural satellite which orbits earth and Sputnik is a man made satellite as it was put into an orbit of the earth.

The period of a satellite is the time taken for the satellite to complete one orbit.

The period of a satellite depends on the height of the satellite above the object it is orbiting.The higher the orbit of the satellite the greater the period and vice versa.

Geostationary Satellite N4

A geostationary satellite is a satellite which: has a period of 24 hours orbits at roughly 36000 km above the earth’s surface which is much higher than other

satellites stays above the same point on the earth’s surface at all times.

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Applications of Satellites N4

Satellites are being used by many countries in different ways. For example: Sending a television or radio signal across the country or to another country

The Olympic Games can be beamed around the world using satellite communication.Three geostationary satellites, placed in orbit above the equator permits worldwide communication with satellites communicating with ground stations in different continents.

NavigationThere are many Global Positioning Satellite (G.P.S) systems available to put in a car so that you don’t get lost. This uses the basic equation d = vt to establish your position.

Weather monitoringThe weather satellite is a type of satellite that is primarily used to monitor the weather and climate of the Earth.

Using Satellites to Monitor Global Change N4 N5

Global environmental change is one of the most pressing international concerns of the 21st century. For many years, various types of satellites have been used to detect and monitor worldwide changes including:

the effects of global warming depletion in the ozone layer and large scale changes in land cover.

These changes have been down to both: natural occurrences and as a consequence of the impact of our actions.

Satellites which are used to monitor such events orbit at heights much smaller than 36000 km and do not stay above the same point on the Earth’s surface. This allows continuous observation and monitoring of the Earth's land, atmosphere, oceans and ice caps.For example, the 2002 oil spill off the northwest coast of Spain was watched carefully by the European ENVISAT satellite, which, though not a weather satellite, flies an instrument (ASAR) which can see changes in the sea surface. It orbits at a height of approximately 800 km. With this information collected by the satellite, rescue teams and environmental agencies can attend the scene quickly and minimise the damage caused.Other disasters, both natural and otherwise can be detected and monitored in a similar way.

Risks Associated with Space Exploration

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Risks N5

Human spaceflight is both risky and expensive. From the crash landing of the first manned Soyuz spacecraft in 1967 to the explosion of the shuttle orbiter Columbia in 2003, 18 people died during spaceflights. Providing the systems to support people while in orbit adds significant additional costs to a space mission, and ensuring that the launch, flight, and re-entry are carried out as safely as possible also requires highly reliable and thus costly equipment, including both spacecraft and launchers.

Challenges During Re-entry N5

When a space craft returns from space it re-enters the Earth’s atmosphere. There are many challenges associated with re-entry and two are listed below:

Rise in temperature due to frictionThe craft is travelling at around 8000ms-1 so a large frictional force acts on it due to the air in the atmosphere. This results in the space craftslowing down. The frictional force causes a rise intemperature which is a problem for the craft. Thespace craft uses special silica tiles to protect itand the bottom and leading edge are covered withblack reinforced carbon. These materials which makeup the Thermal Protection System are designedto absorb large quantities of heat without increasingtheir temperature very much. In other words, they have a high specific heat capacity.The peak skin temperature, on the underside of the wings close to the leading edges, is around 1600°C - hot enough to melt steel.

The angle of re-entryIf the angle of approach is too steep, frictional heating will be too fast and burn the spacecraft up. If the angle of approach is too shallow the spacecraft will skip off the atmosphere into a highly elliptical orbit which will take it far from the Earth (think about skipping a stone across a pond). There is thus an optimum angle for re-entry.

Weight and Mass

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N5N4

N4

From the definition:gravitational field strength = weight

massIn symbol form: g = W W = mg m = W m g

Example: A girl has a mass of 70 kg on Earth (g = 9.8 Nkg-1)a) Calculate her weight on i) Earth and ii) the moon where g = 1.6 Nkg-1.b) What is her mass on the moon?

Solutiona) i) W = ? W = mg ii) W = ? W = mg

m = 70 kg W = 70 x 9.8 m = 70 kg W = 70 x 1.6 g = 9.8 Nkg-1 W = 686 N g = 1.6 Nkg-1 W = 112 N

b) m = 70 kg (mass does not change)

Weight, Mass and Gravitational Field Strength Equation

Weight always acts vertically downwards. Its size does not just depend on the mass of the object, but on the strength of gravity at that place. The strength of gravity in a particular place is called the gravitational field strength (g) and is defined as the weight per unit mass. It is measured in Nkg-1. On Earth, g = 9.8 Nkg-1.

Quantity Symbol SI Unitweight W Nmass m kg

gravitational field

strengthg Nkg-1

Weight

Weight is a force caused by gravity acting on an object’s mass. On Earth, it measures thepull of the Earth on the object. It is measured in newtons (N).

MassMass measures the amount of matter in an object. It is measured in kilograms (kg).The value of mass does not change from place to place.

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N5 W = m g Calculations - During Interplanetary Flight

The value for g is not always constant. It changes as you travel: further away from the centre of the earth; to a different planet, moon or star.

Every planet, moon and star has their own gravitational field strength.

Planet, Moon or Star Value for g / Nkg-1

Mercury 4Venus 9Earth 9.8

Earth’s Moon 1.6Mars 4

Jupiter 26Saturn 11Uranus 11

Neptune 12Sun 270

Example: An un-manned space rocket of mass 20000 kg travels from Earth to Mars, Jupiter, Saturn and Uranus.

a) Calculate the rocket’s weight on Mars.b) What is the mass of the rocket on Jupiter?c) Of the 4 planets (including Earth) visited by the rockets, on which planets would the

weight of the rocket be the same? Explain your answer.

Solutiona) ) W = ? W = mg

m = 20000 kg W = 20000 x 4 g = 4 Nkg-1 W = 80000 N

b) m = 20000 kgc) Saturn and Uranus. The values for g on both planets are the same with the mass of the

rocket remaining constant.

During interplanetary flight there is no need for the engines to be kept on. Since space is avacuum there is no friction acting on the space vehicle. With no unbalanced forces acting onthe vehicle it will continue to move at a steady velocity (Newton’s First Law of Motion).

The Space Rocket

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Resultant Forces N5

Resultant forces in the horizontal direction was studied in the Forces section (1.2).In this section we will consider resultant forces in the vertical direction in the context of a space rocket launching. In this section we will also consider the forces acting on the rocket during flight and when landing. This involves Newton’s 1st, 2nd and 3rd laws of motion and the weight of the rocket (W = mg).

Example 1 - Launching

At launch, a rocket of mass 20 000 kg accelerates off the ground at 12 ms-2 (ignore air resistance)

a) Use Newton’s 3rd law of motion to explain how the rocket gets off the ground.b) Draw a free body diagram to show all the vertical forces acting on the rocket as it

accelerates upwards.c) Calculate the engine thrust of the rocket which causes the acceleration of 12ms-2.

Solutionsa) The rocket pushes the gas out the back downwards (action) and the gas pushes the

rocket upwards (reaction). b)

Weight

Engine thrust

c) Calculate F and WF = m aF = 20 000 x 12F = 240 000N

W = m gW = 20 000 x 9.8W = 196 000 N

F = upward force (thrust) – downwards force (Weight)240 000 = thrust – 196 000thrust = 436 000 N

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Resultant Forces (2) (ctd) N5

Example 2 – During Flight

The same rocket reaches a speed of 10 000 ms-1 as it accelerates away from earth. a) Can you suggest 3 reasons why the acceleration of the rocket will increase? (Hint: this

time take into consideration air resistance)b) When the rocket is in space there is negligible gravity acting on it. Use all of Newton’s

laws of motion to explain how the rocket moves in space.

Solutiona)

Decrease in mass due to fuel being used up Decrease in air resistance as there is less air particles the further away from the

surface of the Earth Decrease in the value of g the further away from the centre of the Earth

b) Travelling at a constant speed – all thrusters are switched off and forces or both forward and backward thrusters are on applying the same force. In both situations the forces are balanced (1st Law)Accelerating – forward thrusters on and the forces are unbalanced in the forward direction (2nd law)Decelerating – backward thrusters on and the forces are unbalanced in the backward direction (2nd law)When the thrusters are on they propel the gases out (action) which applies a force to the rocket in the opposite direction (reaction) (3rd law)

Example 3 – Landing

On returning from space the rocket has to overcome two major hurdles: Re-enter the Earth’s atmosphere Land safely on the ground

a) As the rocket enters the earth’s atmosphere what happens to it’s velocity?b) Explain your answer to part a)c) What is the main energy change during re-entry (think back to S1 Energy topic)?d) When the rocket touches down on the ground, explain in terms of forces why a

parachute is activated out the back of the rocket to bring it to a safe stop.

Solutiona) It decreasesb) The rocket is travelling so fast (at around 8000 ms-1) as it passes into the atmosphere air so

a large frictional force will act against it.c) Kinetic to heatd) When the parachute opens, the force due to air resistance (drag) drastically increases and

causes an unbalanced force acting backwards against motion. This will result in the rocket decelerating and eventually coming to a safe stop.

2.2 Cosmology

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Light Year N4 N5

Contrary to the name, a light year is a measure of distance and not time.

1 light year is the distance light travels in 1 year.

Light is an electromagnetic wave which travels at a speed of 300 000 000 ms-1.

QuestionHow far does light travel in one year?d = ? d = v tv = 300 000 000 ms-1 d = 300 000000 x 31 536 000t = 1 x 365 x 24 x 60 x 60 = 31 536 000 s d = 9 460 800 000 000 000 m

one light year = 9 460 800 000 000 000 m

As the distances in the universe are very large we need to use the term light year instead of metres or even miles. Below are distances you will be required to know.

Approximate distance from Earth to: The Sun – 0.000016 light years (or 8.3 light minutes) Proxima Centauri (nearest star outside the solar system) – 4.2 light years Canis Major Dwarf (nearest galaxy to the Milky Way) – 25000 light years The edge of the known Universe – 46 billion light years.

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The Big Bang Theory (The Theory of the Origin of the Universe) N5

Most astronomers believe the Universe began in a Big Bang about 14 billion years ago. At that time, the entire Universe was inside a bubble that was thousands of times smaller than a pinhead. It was hotter and denser than anything we can imagine.

Contrary to the name, astronomers believe that there was no explosion. The ‘bubble’ began to expand and the Universe that we know was born. Time, space and matter all began with the Big Bang. In a fraction of a second, the Universe grew from smaller than a single atom to bigger than a galaxy and it kept on growing at a fantastic rate. It is still expanding today.

As the Universe expanded and cooled, energy changed into particles of matter and antimatter. These two opposite types of particles largely destroyed each other. But some matter survived. More stable particles called protons and neutrons started to form when the Universe was one second old.

Over the next three minutes, the temperature dropped below 1 billion degrees Celsius. It was now cool enough for the protons and neutrons to come together, forming hydrogen and helium nuclei.

After 300 000 years, the Universe had cooled to about 3000 degrees. Atomic nuclei could finally capture electrons to form atoms. The Universe filled with clouds of hydrogen and helium gas.From these clouds, galaxies and solar systems formed.

Evidence to Support the Big Bang Theory N5

Scientists are reasonably certain that the universe had a beginning. This is the basis of the Big Bang Theory. To support this argument scientists have discovered that:

Galaxies appear to be moving away from us at speeds proportional to their distance. This observation supports the expansion of the universe and suggests that the universe was once compacted.

If the universe was initially very, very hot as the Big Bang suggests, we should be able to find some small remains of this heat. In 1965, Radio astronomers discovered Cosmic Microwave Background radiation (CMB) which spread throughout parts of the observable universe. This is thought to be the small remains which scientists were looking for.

Finally, the abundance of the "light elements" Hydrogen and Helium found in the observable universe are thought to support the Big Bang model of origins.

As mentioned above, the Big Bang occurred about 14 billion years ago. Scientists estimate this by:

Looking for the oldest stars Measuring the expansion of the universe.

The Electromagnetic Spectrum

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Electromagnetic Radiations N5

There is a group of radiations which have given astronomers a vast amount of information on the Universe. These radiations make up The Electromagnetic Spectrum.

Like all the notes on a piano, they are grouped in an order according to their frequency.

In unit 3 you will learn what frequency and wavelength means in Physics but all you have to know in unit 1 is the order in which these radiations fall in terms of their frequency and wavelength.

All these radiations travel at the speed of light = 300 000 000 ms-1.

The 7 radiations are listed below:

How do I remember this?

Rabbits Mate In Very Unusual eXpensive Gardens

Can you think of your own mnemonic to remember The Electromagnetic Spectrum?

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Detectors of Electromagnetic Radiations N5

Humans can detect some of the electromagnetic radiations e.g. the eyes can detect visible light, infra red can be detected by skin and sun burn is a consequence of the skin being over exposed to ultra violet radiation from the sun. However, energy is given out by objects in space (e.g. stars or galaxies) over the whole range of the electro-magnetic spectrum so to fully understand the universe we must collect information at all these wavelengths. Different kinds of telescope are therefore required to detect different wavelengths of radiation as one as alone cannot detect them all.

Below is a list of detectors for each radiation in the spectrum.

Radiation Detector Use

Radio and T.V AerialGives information on different planets e.g.

distance from the Earth

Micro waves Diode probe

The detection of Cosmic Microwave Background

consolidated the belief the Big Bang occurred

Infra Red Blackened thermometer

Infra red is used to detect objects just outside the

visible spectrum

Visible Light Photographic filmGives information on planets

and stars including temperature and size

Ultra Violet Fluorescent paintUsed to study star formation

– most “young” stars emit ultra violet radiation

X-Rays Photographic film Used to detect the presence of black holes

Gamma rays Geiger-Muller tube Used to detect the presence of black holes and supernova

Spectroscopy

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Continuous and Line Spectra N5

Astronomers can find out information about stars from the light the star emits using an instrument called a spectroscope. The spectroscope splits up the light to produce a spectrum.There are two types of spectra:

Continuous – produced by light from solids, liquids and gases at high pressure and at high temperature. Each colour in the spectrum has a different frequency and wavelength.

Line – produced by hot gases at low pressure and gases which have an electric current passed through them. Each line in the spectrum corresponds to a particular frequency and wavelength.

Line spectra are extremely useful for astronomers because every chemical element has its own unique spectrum (like D.N.A or fingerprints). This allows astronomers to identify elements present in distant stars.

You may find this easier to understand after looking at the example on the next page.

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Stellar Detectives N5

Example: Identify the elements that make up the unknown star from the line spectra below. The line spectra for hydrogen, helium, sodium and calcium are given below to help you.

Unknown star

Hydrogen

Helium

Sodium

Calcium

Answer : Hydrogen and Helium. All spectral lines present in Hydrogen and Helium are present in the unknown

star.