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February 2005

Tutor support materials

GCSE

Edexcel GCSE Astronomy

Student Workbook

Edexce

lGCSEin

Astronomy

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Edexcel Limited is one of the leading examining and awarding bodies in the UK andthroughout the world. It incorporates all the qualifications previously awarded underthe Edexcel and BTEC brands. We provide a wide range of qualifications includinggeneral (academic), vocational, occupational and specific programmes foremployers.

Through a network of UK and overseas offices, our centres receive the support theyneed to help them deliver their education and training programmes to learners.

For further information please call Customer Services on 0870 240 9800, or visit ourwebsite at www.edexcel.org.uk

Authorised by Jim DobsonPrepared by Sarah Harrison

All the material in this publication is copyright Edexcel Limited 2005

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Contents

Introduction 1

Symbols, Units and Data Required 3Basic Science Knowledge 7Unit 1 Planet Earth 11

The Earth 11

Days and Seasons 17

Exercise 1 21

Project 1: Making a Model Earth 24Unit 2 The Moon and the Sun 25

The Moon 25

The Sun 27

Eclipses 31

Exercise 2 33

Project 2: Observing the Sun and Moon 37

Unit 3 The Solar System 39Planets and Asteroids 39

Meteors and Comets 54

Exercise 3 58

Project 3: Researching the Solar System 61

Unit 4 Stars and Galaxies 63Constellations 63

Stars 68

Galaxies 78

Exercise 4 87

Project 4: Constructing a Star Map 91

Unit 5 Observing Techniques and Space Exploration 93Observing the Universe 93

Exploring the Universe 102

Exercise 5 112

Project 5: Building a Telescope 116

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Answers 117Exercise 1 117

Exercise 2 120

Exercise 3 122

Exercise 4 125

Exercise 5 128

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Students Workbook Edexcel GCSE in Astronomy Issue 1 February 2005 1

INTRODUCTION

This workbook has been developed to offer support to learners when studying GCSEAstronomy qualification, and to teachers delivering the course.

The aim of this booklet is to offer learners and teachers information that will providesupport when starting the course. This booklet also offers support for revision and forlearners to enhance your learning, using research and web-based activities, for eachunit.

Each unit gives learners the opportunity to support the development of theircoursework and shows learners what is required for each task. The specificationprovides details on the coursework requirements.

An exemplar project has been included at the end of each unit. They have beendesigned to make the course more interesting and give the learner the chance to usethe project work as a way to understand all the astronomy information that youneed.

At the end of each unit there is also an exercise to test the learners understanding,and answers are provided at the end of the workbook.

Edexcel wishes to acknowledge the help and support received in the completion ofthis workbook, particularly the Royal Observatory Greenwich for their technicalediting and support.

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Students Workbook Edexcel GCSE in Astronomy Issue 1 February 20052

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SYMBOLS,UNITS AND DATA REQUIRED

You are expected to understand and use the following terms:

The 24 hour clock

The use of hours, minutes and seconds for measuring time

The celestial co-ordinate system: (explained further in Unit 4 page 68)

right ascension (RA) celestial longitude, measured in hours

declination (dec) celestial latitude, measured in degrees ()

The units for measuring angles:

degree

arc minute 1/60th of a degree arc second 1/3600th of a degree

The units for temperature:

kelvin (K) 0 K = 273C

degree Celsius (C) 0C = 273 K

The unit of power (luminosity):

Watt (W) Joule per second

The units of length:

astronomical unit (AU) the mean distance between the Earth and the Sun(150 million km)

light year (l.y.) the distance travelled by light in a vacuum in 1 year(63240 AU)

parsec (pc) the distance at which a star would have parallax of 1 second ofarc (3.2616 l.y.)

The speed of light in a vacuum = 300000 km/s

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In exams you are expected to remember and use the following approximate values:

Earth diameter = 13000 km

Moon diameter = 3500 km

Sun diameter = 1.4 million km

mean Earth-Moon distance = 380000 km

mean Earth-Sun distance = 150 million km = 1 AU

difference in magnitude of 1 = brightness ratio of 2.5

difference in magnitude of 2 = brightness ratio of 100

(see apparent magnitude on page 69)

The following information may be useful to you.

Powers of ten

In astronomy the numbers written can be extremely large or extremely small.Therefore, they are often written in scientific notation, as powers of ten.

Eg the diameter of the Earth is approximately 13000km. This can be written as1.3 x 104 km.

101 = 10

102 = 10 x 10 = 100

103 = 10 x 10 x 10 = 1000 k kilo

106 = 10 x 10 x 10 x 10 x 10 x 10 = 1000000(one million)

M Mega

109 = one thousand million = one billion G Giga

100 = 1

101 = 1/10 = 0.1

102 = 1/(10 x 10) = 0.01 c centi

103 = 1/(10 x 10 x 10) = 0.001(one thousandth)

m milli

106 = 1/(10 x 10 x 10 x 10 x 10 x 10) = 0.000001(one millionth)

micro

109 = one billionth n Nano

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The Greek alphabet

Letters from the Greek alphabet are often used in astronomy, eg when namingstars.

alpha beta

gamma delta

epsilon zeta

eta theta

iota kappa

lambda mu

nu xi

omicron pi

rho sigma tau upsilon

phi chi

psi omega

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BASIC SCIENCE KNOWLEDGE

The following knowledge of some aspects of science is needed to understand parts ofthis astronomy course.

1 Reflection when light bounces off a shiny or smooth surface.

2 Refraction when light passes from one medium to another (of a differentoptical density) it changes direction.

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3 Spectrum of colours when white light passes through a prism it disperses intothe seven colours of the spectrum (red, orange, yellow, green, blue, indigo, andviolet).

4 Electromagnetic spectrum this contains electromagnetic (EM) waves. In theEM spectrum they are placed in order of their frequency and wavelength.Wavelength is the distance from one peak of a wave to the next peak. All of thedifferent wavelengths are used in astronomy.

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5 Atomic Structure the structure of atoms is widely used in astronomy, eg foridentifying the elements within stars when looking at their spectra. Theelements most commonly looked at by astronomers are hydrogen and helium,which are found in stars such as the Sun.

6 Speed speed can be calculated using the following equation:

time

cetandisspeed =

Speed is measured in metres per second (m/s)

Distance is measured in metres (m)

Time is measured in seconds (s)

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Unit 1 Planet Earth

The Earth

The Earth is the third planet from the Sun and it has one natural satellite, called theMoon. The Earth has a mean diameter of 13 000 km and is approximately 150 millionkm from the Sun. This distance from the Sun is also known as 1 AU (astronomicalunit). The Moon is approximately 380000 km from the Earth and has a mean diameterof 3500 km.

Figure 1.1: The Earth from space (NASA)

Orbit

The Earths orbit around the Sun is not quite circular, but elliptical. So at somepoints it is closer to or further from the Sun. The closest point to the Sun is calledperihelion, and the furthest is called aphelion. As the orbit is elliptical, 1 AU is themean (average) distance from the Earth to the Sun over a year (one orbit). Allplanets have elliptical orbits.

Figure 1.2: Perihelion and aphelion

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Figure 1.2 is not to scale, and shows the orbit as very elliptical. The orbits of theplanets around the Sun are more circular, with the exception of Pluto.

Latitude and longitude

The imaginary great circle around the Earths surface is the Equator. Thegeographical equator is equal distance from the north and south poles and is at 90to the angle of the Earths axis.

The Earths surface is divided with imaginary lines. Latitude lines are horizontal, andon the celestial sphere they tell the angular distance from an object in space to theecliptic (line). Lines of Longitude are vertical and mark the time difference aroundthe world from the Greenwich Meridian. Each 15 difference in longitude is onehours difference in time. East of Greenwich the time is ahead of Greenwich MeanTime (GMT), west of Greenwich is behind GMT.

Geology

The crust on the Earth consists of several rocky plates that move due to currents inthe hot rocky mantle below.

The structure of the Earth has been determined by monitoring seismic waves fromearthquakes.

Figure 1.3: The structure of the Earth

The Earth has a dense core, rich in iron and nickel. The outer part of the coreextends down to 5150 km, but the inner core is 2460 km in diameter. The inner coreis liquid because of the higher pressure there. The core is surrounded by a mantle of

silicate rocks. This extends to a depth of 2890 km. The thin outer layer of lighterrock is called the crust. Continental crust can be up to 50 km deep, but oceanic crusthas an average depth of 10 km.

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Oceans

The oceans cover approximately 70% of the Earths surface and are unique in oursolar system. No liquid water has been discovered on any other planets and moonsthough water ice has been discovered. The average depth of the oceans is 3795 m.However, the deepest part of the oceans is the Mariana Trench, which is

approximately 11 000 m deep. This is located in the Pacific Ocean, where two platesjoin and one is subducted under the other to form the trench.

The average temperature of the oceans is 3.9C. They absorb heat energy from theSun and store it. The ocean currents distribute this heat energy around the Earthheating the land and air during winter and cooling it during summer.

The Earth has ice caps at its north and south poles. These are formed because thetemperature is below freezing throughout the year. The north polar ice cap hasthinned recently as the temperature has become warmer.

Tides

The oceans have tides which are caused by the gravitational pull of the Moon and theSun. As the Earth spins on its axis once each day it rotates under the tidal bulges.Hence each place has two high tides and two low tides each day. When the Earth,Moon and Sun are all lined up (as in Figure 1.4 diagram 1) the gravity of the Moon andthe Sun combined makes the tide much larger. When the Moon is not lined up withthe Earth and the Sun (as in Figure 1.4 diagram 2) the Moon and the Suns gravity arenot combined so the tide is smaller. The Moon hasthe larger affect on the tides whenit is closer to the Earth. The position of the Moon, relative to the Earth, affectsdifferent parts of the Earths seas. The tides are also affected by the phases of theMoon.

Figure 1.4: Causes of spring and neap tides

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The atmosphere

The atmosphere of the Earth contains approximately 78% nitrogen, 21% oxygen, and1% of other gases such as carbon dioxide, water vapour and argon which havepromoted life. The oceans keep the planet warmer, by retaining some of the Sunsheat and this has also helped life to develop.

The atmosphere makes the sky appear blue. The dust particles in the atmosphere areapproximately the same size as the wavelength of blue light. This means that theyscatter (refract) blue light more than any other colour. Therefore, the colour of lightthat we see is the colour that is scattered the most, which is blue.

When the sun begins to set the light must travel farther through the atmospherebefore it gets to you. More of the light is scattered. As less light reaches you directly,the sun appears less bright. The colour of the sun itself appears to change, first toorange and then to red. This is because even more of the blue light is scattered. Onlythe longer wavelengths are left in the direct beam that reaches your eyes and theseare mostly the red and orange colours.

The sky at the time of a sunset may take on many colours. Sunsets with the mostcolours occur when the air contains many small particles of dust or water. Theseparticles scatter light in all directions. Then, as some of the lightheads towards you,different amounts of the shorter wavelength colours are scattered. You see thelonger wavelengths and the sky appears red, pink or orange.

This happens due to the dust particles in the atmosphere and is due to the nature ofthe particles random motion. As the particles move, there are naturally some areasof the atmosphere with more particles than others. Therefore, the density of theatmosphere is not uniform. This acts in a similar way to dust particles and scattersthe sunlight as it enters the atmosphere. However, this would happen if there wereno dust particles in the atmosphere at all. The presence of dust particles just

increases this process.

For astronomers there are benefits and drawbacks of the Earths atmosphere. Someof these are:

Benefits Drawbacks

Protection against UV rays There are often too many clouds toobserve the skies

The mixture of gases and the temperature

is good for life

There is often too much pollution for

good observations

Astronomers sometimes have difficulty in making astronomical observations,particularly in Britain, as the conditions for observing the sky can be affected by:

optical (light) pollution, which causes poor visibility of the skies, so obscuring thestars

chemical pollution, which causes poor visibility due to the pollutants in the air

interference from radio signals, which is a problem when astronomers are usingradio telescopes.

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The best place in Britain to observe is in the countryside (ideally the middle of a bigfield or on a hill). The best place to site an observatory however would be:

at a high altitude, to give as many cloudless nights as possible

nearer the equator, for better weather

away from towns so the level of light pollution is lower.

Magnetic field

The magnetic field of the Earth is similar to that of a bar magnet. The Earth has amagnetic north and a magnetic south pole. It is the interactions between the liquidouter core and the solid inner core that produce the magnetic field of the Earth.

Magnetosphere

This is the area of space around the Earth that is controlled by the Earths magneticfield. This reaches out 600000 km into space, in the direction of the Sun, but muchfurther in the other direction. The solar wind changes the shape of themagnetosphere and also prevents a lot of the particles in the solar wind fromreaching the Earth.

Van Allen belts

The Van Allen belts are zones of highly charged particles in the Earths magneticfield (magnetosphere). As charged particles in the solar wind are blown off the Sun

the Earths magnetic field traps them and brings them down towards the Earth.There are two Van Allen belts. The outer belt contains mostly electrons and the innerbelt contains mostly protons.

Figure 1.5: The structure of the Van Allen belts

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Aurorae

These are beautiful, flickering illuminations in the night sky that are most often seenwhere the Van Allen belts are closer to the Earth (the ends of the belts). These lienear the north and south polar regions. Where the solar wind interacts with thecharged particles we can observe colourful patterns of light called aurorae. The

aurorae are more intense when there is more solar activity, such as a prominence.

The aurorae have different names depending on where they reach the Earth.

The Aurora Borealis The Northern Lights.

The Aurora Australis The Southern Lights.

Figure 1.6: An example of an aurora (NASA)

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DAYS AND SEASONS

Celestial Sphere

The celestial equator is equal distance from the celestial poles, on the celestialsphere, and at 90 to the angle of the Earths axis.

The Earth rotates from west to east so the Sun appears to move across the sky fromeast to west. As this happens parts of the Earth are in daylight whilstother parts arestill in night-time.

A local meridian is the line that passes from the north pole, under your feet (nadir)to the south pole.

The ecliptic is the line that the Sun appears to travel along. It is actually the planeof the Earths orbit around the Sun.

Seasons

The Earths axis is tilted at 23.5 from perpendicular to the plane of the ecliptic, andthis causes the seasons.

Figure 1.7: The Earths tilted axis

During the seasons some parts of the Earth point towards the Sun, whilst other partspoint away from the Sun. This means that their temperatures are different.

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Figure 1.8: The changing seasons of the Earth

At the equator the temperature does not change very much during the seasons. Thisis because this area receives more direct sunlight throughout the year.

In the temperate regions the seasons show a bigger change in temperature, as theregions point towards or away from the Sun and receive less direct sunlight.

In the polar regions there is a big difference between the amount of sunlight insummer and winter. This is because these regions do not receive very much sunlight

for six months and continuous sunlight for six months. Therefore six months of theyear is daylight, whilst the other six months is night-time.

Equinoxes

These are the times of year when day and night are of equal length on all parts ofthe Earth. There are two equinoxes.

Spring equinox this marks the beginning of spring and is often called thevernal equinox. It occurs on 21st March. This is where the ecliptic crosses thecelestial equator with the Sun apparently travelling north.

Autumnal equinox this marks the beginning of autumn. It occurs on 22nd or 23rdSeptember. This is where the ecliptic crosses the celestial equator with the Sunapparently travelling south.

Solstices

These are the times of year when the Sun appears to be furthest north or south ofthe equator. There are two solstices.

Summer solstice in the northern hemisphere this is the longest day of the year.

It occurs on 21st

June. Winter solstice in the northern hemisphere this is the shortest day of the year.

It occurs on 21st December.

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Days

We can use a shadow stick to measure how the angle of the Sun has changed. If youput a stick in the ground it will have a shadow on a sunny day. At noon the shadowwill be shortest and at sunset or sunrise it will be longest. In summer at noon the

shadow will be shorter than in winter, because the Sun is higher in the sky insummer. By measuring the length of the shadow you can observe how the altitude ofthe Sun changes during the seasons. This can help you to calculate the time of localnoon and thelongitude of where you are observing.

According to astronomy a day is the time it takes the Earth to rotate once on its axis.This takes 23 hours and 56 minutes (23 h 56). A year is the time it takes the Earth toorbit the Sun once. This takes 365.25 days. Also in astronomy there are differenttypes of days. An apparentsolar day is the time between two successive local noons(ie 2 successive meridian transits of the Sun). However, the Suns apparent motionthroughout the year varies. A mean solar day is 24 hours (24 h) long. This is theaverage time calculated for a day, assuming that the Sun travels along the celestial

equator at a uniform rate.This means that there is a need for time zones as different parts of the Earth havenoon (when the Sun is directly overhead at your zenith) at different times. The timezones help when people travel all over the world so they are not constantly changingtheir clocks to the local time.

Solar terms

There are some specific terms needed in astronomy for describing the Sun.

Mean Sun this is an average time for an imaginary Sun moving along the

celestial equator. The true Sun travels at a variable rate, so we cannot use this asa measure of time.

Mean solar time this is the time based on the mean Sun, which travels at auniform rate along the celestial equator.

Apparent solar time this is the time as observed on a sundial.

Equation of time this is the difference between the solar time on a clock andthe apparent solar time on a sundial. The maximum difference is 16 and occurs inearly November. The difference is zero on four occasions. These are 15th April,14th June, 1st September and 25th December.

equation of time = apparent solar time mean solar time

Sundials

Another simple way to observe the changes in the Suns position over a year is to usea sundial. Sundials have been used since ancient times as a method of telling thetime. The main types of sundials are horizontal sundials, that lie flat on a stand, orvertical sundials that are fixed to walls. They all use the same principles. Inequatorial sundials the graduations for the dial are 15 apart, as the Earth rotates by

this distance in one hour. The gnomon (part that casts the shadow) should be at the

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angle of latitude for the place that the sundial is to be used (eg 51.5 N forGreenwich). This means that sundials are specific to one area. The gnomon should beplaced north-south, with the raised end pointing north.

Figure 1.9: Sundials and the angle of the gnomon

Sidereal day

A sidereal day is measured with respect to the stars. It is the time taken betweentwo successive crossings of the star across the observers meridian. It is also the timebetween two successive crossings of the spring equinox across the observersmeridian. A sidereal day takes 23 h 564.

Figure 1.10: A sidereal day and a mean solar day

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EXERCISE 1

Questions

1 Describe the size and position of the Earth.

2 Describe the shape of the Earths orbit around the Sun.

3 Explain the following terms:

a equator

b ecliptic

c perihelion

d aphelion

e latitude

f longitude

g pole

h meridian

i zenith

j horizon

k astronomical unit

l mean Sun

m mean solar time

n apparent solar time

o a year

p a day

q a solar day

r a sidereal day

s equinox

t solstice

u a horizontal sundial

v a vertical sundial

w a gnomon.

4 One Astronomical Unit (1 AU) assumes that the Earth has a circular orbit aroundthe Sun.

a Why is this wrong?

b Why do we still use 1 AU if it is inaccurate?

5 Explain how the Earth is distinguishable from the other planets in our SolarSystem.

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6 Explain how the Moon and the Sun affect the seas and oceans on Earth.

7 Explain why the sky is:

a blue (most of the time)

b red at sunrise and sunset.

8 Describe two benefits and two drawbacks of the Earths atmosphere for thefollowing people:

a the general population

b astronomers.

9 Explain what these types of pollution are:

a chemical pollution

b optical pollutionc radio interference.

10 Where are the Van Allen belts and state their composition?

11 Explain where and how Aurorae are formed.

12 Does the Earth spin clockwise or anticlockwise on its axis?

13 Does the Earth orbit the Sun in a clockwise or anticlockwise direction?

14 Why are time zones needed across the Earth?

15 Explain how the tilt of the Earth and its orbit around the Sun gives us seasons.

16 What do astronomers measure with a shadow stick and what can thesemeasurements show throughout a year?

17 On a sundial what angle does the gnomon correspond to?

18 Why does the Sun rise and set at different times throughout the year?

19 What is the equation of time?

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Research

1 Find out what the different layers are in the Earths atmosphere (from theinternet or textbooks).

2 Find out about the Campaign for Dark Skies and the International Dark SkiesAssociation.

3 Find out what the desirable conditions are for siting an observatory.

4 Find diagrams (from the internet or textbooks) to show the location of the VanAllen belts.

5 Find pictures of the Aurorae and find the difference between the Aurora Borealisand the Aurora Australis.

6 Carry out a shadow stick experiment, on two different sunny days, and on eachday observe and measure how the shadow length varies. This can become part ofyour coursework. Use the results from this to determine the following:

a the length of the shadow at noon

b the time of local noon

c the longitude at which you carried out the experiment.

7 Draw a template to make a sundial (face and gnomon). Construct the sundial andtest its accuracy on at least three widely separate occasions. This could be usedas part of your coursework.

8 Find a graph for the equation of time showing how the solar time differs duringthe year. Identify on the graph the times of the year that the equation of timeequals zero, and which time of the year it is at its maximum.

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PROJECT 1:MAKING A MODEL EARTH

Introduction

This project is to make a model of the planet Earth in order to help you understandthe ideas that are covered within this unit.

Resources

A papier mach model would be most suitable as this would be light enough to use indemonstrations and could be decorated to show all of the features of the Earth.Suggested resources include:

balloons

paper (newspaper is suitable)

wall paper paste (or similar adhesive)

paint

brushes (for paint and paste)

a variety of arts and crafts materials to decorate the model

pictures of the Earth showing all its features.

Method

Construct the papier mach model of the Earth and paint it to resemble the land andoceans. You may wish to extend your model by adding atmosphere, clouds and aurorawith a little creative thinking. The models can then be used to simulate the motionof the Earth around the Sun, rotation of the Earth and the seasons.

Links to the specification

This project covers the Days and Seasons part of this unit (1.161.21) and areas ofThe Earth part of this unit (1.11.13).

When to start

This project could be started at the beginning ofUnit 1, and you could use andimprove on your model as you learn about the various aspects ofUnit 1:PlanetEarth.

Documents

34600721-Unit-1