Campo magnético - guia de exploração (Projeto AstroPi)

1. Magnetic Earth
Learning about, and investigating, the magnetic field of the Earth
An AstroPi Learning Resource for Secondary Schools

2. 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.

3. 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

4. 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.

5. 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

6. SEEKING
INSPIRATION?
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

7. SEEKING
INSPIRATION?
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

8. SEEKING
INSPIRATION?
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

9. SEEKING
INSPIRATION?
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

10. SEEKING
INSPIRATION?
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

11. SEEKING
INSPIRATION?
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

12. SEEKING
INSPIRATION?
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