Magnetic Earth Learning about, and investigating, the magnetic field of the Earth

An AstroPi Learning Resource for Secondary Schools

Introduction:

Understanding the magnetic field of the Earth, and its role in protecting the Earth,

is crucial to society. There is some evidence that Mars once looked very much like

Earth, with an atmosphere and oceans of water. Once Mars lost its magnetic field

and the protection offered from the solar wind, however, it was only a matter of

time until it lost its atmosphere and oceans too.

Satellites not only provide a unique perspective of our planet but also allow us to explore the

universe. To do this effectively, satellites house a wide array of instruments to detect their

surrounding environment called sensors. Similar to how we use a compass on the ground to

point towards North, satellites use magnetometers to sense the Earth’s magnetic field in-order

to determine which direction they are pointing.

How to use this guide:

This teacher guide, and the resources that accompany it, can be used in different ways:

Following the activities in sequence will cover all of the curriculum links listed below. This might

be done as part of a collapsed timetable day, or over a series of sessions. This would give a

thorough preparation for meeting the challenges and entering the competition, regardless of

prior learning.

Teachers can pick and choose which activities, resources and links to use and when – they can

be used independently of each other. This might enhance the ways in which space and

magnetism topics are currently taught. If teachers have specific challenges in mind that align

with their interests and those of the children, the supporting learning activities might be

selectively chosen.

Teachers may wish to present children, in class or as part of an extra-curricular activity, with the

challenges only. Please note – the challenges are merely suggestions, and schools are

completely free to use the AstroPi in any way they see fit to enter the competition.

Other documents accompanying this guide:

information from the Raspberry Pi foundation, all about the AstroPi and Raspberry Pi,

information from organisations within UK Space, explaining the importance of several themes of

space exploration and technology,

AstroPi competition details and entry form,

Competition entry project planning guidance for teachers and students.

Curriculum Links:

Lower Secondary Chemistry Content:

the composition of the Earth (partial coverage)

the structure of the Earth

Lower Secondary Physics Content:

magnetic poles, attraction and repulsion

magnetic fields by plotting with compass, representation by field lines

Earth’s magnetism, and compass navigation

the magnetic effect of a current

Upper Secondary content: describe the attraction and repulsion between unlike and like poles for permanent magnets and

explain the difference between permanent and induced magnets

describe the characteristics of the magnetic field of a magnet, showing how these effects

change direction from one point to another, and explain how this links to the forces magnets

exert on each other without actual contact

Relate the characteristics of a magnetic compass to evidence that the core of the Earth must be

magnetic

Learning Activities

1. Basic magnetism. Revision of prior learning - This resource from the Institute of Physics provides

students with a review of basic magnetism concepts, which they probably covered in primary

school science lessons1

The resource covers:

magnetic poles,

magnetic materials,

attraction and repulsion,

simple electromagnetism.

2. Magnetic Fields. The first part of this teacher guide provides pointers on introducing flux and

lines of force via some simple experiments. It then goes beyond what would be expected at age

14-16, moving on to calculations and flux density. Recognition of the shape of a field produced

by a simple dipole magnet helps students to recognise the similar field produced by the Earth’s

outer core.

3. Nature and Source of Earth’s Magnetic Field. The short PowerPoint presentation ‘magnetic

Earth’ (with speaker notes) shows how the field of the Earth is similar to that of a bar magnet –

a dipole. The origin of the magnetic field is not covered in depth – indeed it is not fully

understood by scientists. Current models hypothesise that the solid iron core is surrounded by a

molten outer core containing, among other materials, iron. Movement of this conductor, caused

by heat and the rotation of the Earth, induces a magnetic field – this is known as a geodynamo.

It is shown in the presentation that this is a similar pattern, too, to that created by a solenoid

carrying a current.

4. Magnetism and Compasses. The properties of magnets have been known, but not understood,

for thousands of years. Ships have carried compasses for navigation for many years – these were

created by stroking a magnetic metal with a lodestone. This is a magnetic rock containing

magnetite. Compasses are useful for map-work, using landmarks found on a detailed map to

navigate with great accuracy. They are also critical for occasions when no landmarks are visible –

at sea, or in deserts and in forests etc. Further historical information can be found on this Royal

Museums Greenwich web page.

1 A National STEM Centre login is required - registration is free and quick. This and all other National

STEM Centre elibrary resources are free to access and use.

At this point, some simple navigation tasks using a map and compass might reinforce the

importance of compasses. Students can also make their own compass – the simplest method is

shown in this presentation (slide 6). To magnetise their own ‘needle’ in the same way as the

ancient seafarers, children can stroke a nail or paperclip repeatedly with a permanent magnet.

This will partially magnetise the metal which can then be floated on a cork or similar, allowing

the magnet to rotate freely and align itself with the field lines pointing towards the magnetic

poles.

5. Investigating the Earth’s Field. The magnetic field of the Earth can be investigated with a

compass. Deflections in the field can be observed by bringing other magnets nearby, by electric

currents and by the presence of massive pieces of non-magnetised, magnetic materials.

Activities 3 and 4 in this resource describe practical activities investigating the shape of magnetic

fields in 3-dimensions, leading to discussion of the Earth’s field declination.

6. Changes in the Earth’s Field. Extending the investigation of the Earth’s magnetic field - Magnetic

striping of the mid-Atlantic ridge provides evidence that the poles have flipped at points in

history. Activity E5 in this resource explains the scientific background to this, and shows how this

can be simulated in the lab using simple equipment.

Further Links:

NASA investigation of the solar wind: http://solarscience.msfc.nasa.gov/SolarWind.shtml

Alien atoms and the solar wind (ESA): http://sci.esa.int/cluster/2569-solar-wind/

Detail related to the Geodynamo Theory (University of California, Santa Cruz):

http://www.es.ucsc.edu/~glatz/geodynamo.html

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? The magnetic field of the Earth looks like that of a bar magnet. By measuring the strength and direction of this field is it possible to pinpoint your location, even in space? Can you measure longitude and latitude? A small, cheap, reliable navigation device would be very useful to astronauts, and might even be wearable.

Image credit: ESA

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The solar wind is a blast of radiation and charged particles that streams out of the sun in all directions. It is especially powerful during solar storms, and is the cause of the aurora seen in the Arctic and Antarctic regions. The Earth's magnetic field protects us from the harmful effects of the solar wind. In doing so it is squashed and squeezed. Is it possible to measure the shape of the magnetic field while also looking for ionising radiation? Understanding how to protect astronauts from the solar wind will be critical for extended space travel.

Image credit: NASA

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The Earth's magnetic field changes over time. The poles can move - the North Pole has moved up to 40km in a year! Sometimes the North and South poles even swap - although this hasn't happened for around 800,000 years. As the ISS orbits the Earth, is it possible to track any movement of the poles? It would be important to know where the ISS is. To do that, it is vital to accurately know the time.

Image credit: NASA

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The Sun has a powerful magnetic field, and the solar wind also creates a magnetic field as it blows outwards. Does this magnetic field vary when the ISS passes into the earth’s shadow? Understanding more about the solar wind can help prevent major electrical 'blackouts' on Earth

Image credit: ESA

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At extreme northern and southern latitudes, particles from the sun are funnelled by the Earth's magnetic field. As they strike the atmosphere they cause gas to be excited and to give out light. These beautiful displays are known as the Northern and Southern Lights (or the Aurora Borealis and the Aurora Australis to give them their proper scientific names). Could these displays be photographed from the ISS without depending on the busy astronauts? Projects that automate tasks for the astronauts allow them to do other, more important and interesting things – just like labour-saving devices such as dishwashers in our homes!

Image credit: NASA

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The continental crust of the Earth contains materials different to those found in the oceanic crust where more magnetic material can be found. Does this lead to differences in the strength and direction of the field in different locations? Can the whereabouts of any anomalies be pinpointed accurately?

Image credit: ESA

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Some experiments on board the International Space Station, such as the AMS (Alpha Magnetic Spectrometer), use very strong magnetic fields. AMS contains a strong permanent magnet, and will help to detect cosmic rays for many years to come. Can the effects of these magnets be measured inside the space station? Magnetic interference can interfere with delicate instruments and experiments, and every effort is made to shield from its effects. Has the shielding worked?

Image credit: NASA