1
Unit
THE EARTH IN THE
UNIVERSE
1. WHAT IS THE UNIVERSE
LIKE?
 The origin of the Universe is explained by the
BIG BANG THEORY. This theory describes
how the universe expanded from a point with
all the matter concentrated in it. It had a very
high temperature and exploded and formed
the celestial bodies in the Universe.
• Different models have been proposed to explain
the Earth’s position in the Universe:
• The GEOCENTRIC MODEL:
 It states that Earth is the centre of the
Universe. The Sun and all planets orbited the
Earth. It was proposed by Ptolomy in the 2nd
century
 The HELIOCENTRIC MODEL:
 It states that the Sun is the centre of the Universe and
the rest of the planets revolve around it. This model
was proposed by Nicolaus Copernicus in 1942.
 In 1610, Galileo Galilei invented the telescope and
proved the heliocentric theory.
2. WHAT MAKES
UNIVERSE ?
UP
THE
 Galaxies
 Planets
 Dwarf planets
 Asteroids
 Comets
 Stars
 Nebulas
 Supernovas
 Satellites
Activity: Complete the
crossword and then copy the
definitions of each component of
the Universe in your vocabulary
organiser
2. WHAT
SYSTEM?
MAKES
UP
THE
SOLAR
TO STUDY: Complete this concept map
The planets
The planets are celestial bodies that orbit the sun, there
are two types, inner planets and outer planets.
4. HOW DO PLANETS MOVE?
 Planets have 2 movements:
 ROTATION and REVOLUTION
 The Rotation period is the time a planet takes
to turn around its own axis. It is “a day”.
 For example, the Earth’s rotation period is 24
hours, but the rotation period in Venus it is 243
terrestrial days.
 The Revolution period is the time a planet
takes to revolve around the Sun. It is “ a year”.
 For example, the Earth’s revolution period is 365
days and 6 hours, but Venus has a revolution
period of 224 days.
Question: What is special about the revolution period
and the rotation period in Venus?
The rotation period in Venus is longer thant its
revolution period, this means, in Venus a day is longer
than a year
5. WHICH ARE INNER PLANNETS?
• Inner planets are the smallest and nearest to the sun.
• They are rocky planets, because the crust and the
mantle are made of rock (the core is metallic).
Earth
Mercury
Venus
Mars
5. WHICH ARE OUTER PANNETS?
Neptune
Jupiter
Saturn
Uranus
They are bigger and farther to the Sun. They are called
gas giants because they consist mainly of gases.
Remmember, there are other
celestial bodies apart from
planets in the solar system…
Dwarf planets
Some dwarf planets are:
Pluto
Ceres
Eris
Haumea
Makemake
Small Solar Bodies
Asteroids are rocky objects wich orbit the sun.
They are iregular shape
and most of them are a
few meters wide.
Small Solar Bodies
Comets orbit the Sun also, but they do it in highly elliptical
orbits
They are made of ice and gas, and when they are near to
Sun, his ice evaporates creating a bright tale.
Satellites
 Natural satellites revolve around planets.
 Some planets have a lot of satellites (Like
Jupiter)
 Some others have just 1 satellite, like our
Moon, in the Earth.
 Mercury and venus don’t have any.
7. HOW DOES THE EARTH MOVE?
 The Earth’s ROTATION auround its axis takes 23
hours, 56 minutes and 4 seconds. It causes the
sequence of day and night.
 The Earth’s REVOLUTION around the Sun takes 365
days and 6 hours (a quarter of a day). It is an ellipse
but the Sun is not exactly in the middle… Revolution
movement causes the seasons. But it is not the only
reason for the seasons…
 Watch the video in the blog : «The reason for the
seasons»
https://www.youtube.com/watch?v=Pgq0LThW7QA
Then…
 What causes the seasons?
 The revolution of the Earth around
the Sun
 The tilt of the Earth’s axis.
The tilt of the axis makes the seasons occurs at different
times of the year in the Northem and Southern hemisphere.
When it is summer in the Northem hemisphere it is winter in
the Southern hemisphere and viceversa.
So, why is summer warmer than winter?
• In summer solar rays strike perpendicular to the Earth’s surface (at
a right anlge, more directly). So, it heats up more.
• In winter solar rays strike the Earth at a steeper angle (less
directly), and it heats up less.
Have a look to the seasons simulator in my blog to see how
the solar rays strike into the Earth’s surface at different
seasons:
http://astro.unl.edu/classaction/animations/coordsmotion/ecli
pticsimulator.html
What is happening in the
rest of the seasons?
 The first day of AUTUMN is the 23rd of
September. Day and night takes the same
time. It is the autumn equinox.
 Then, days get shorter and nights get longer
until 22nd of December, the shortest day, the
winter solstice. It is the first day of WINTER.
 Then, days get longer and nights get shorter
until 21st of March, where day and night
takes the same, the spring equinox. It is the
first day of SPRING.
 Finally, days get longer and nights get shorter
until 21st of June, the longest day. It is the
summer solstice, SUMMER begins.
10. WHAT IS THE EARTH LIKE?
 The Earth has special characteristics that
allow LIFE on it. This characteristics are:
 An atmosphere with oxygen to breath and
carbon dioxide for the plants to make their on
food (through photosyntesis).
 An average temperature of 15 º
 A water cycle
Different “Spheres” make up
the Earth
 Geosphere
 Atmosphere
 Hydrosphere
 Biosphere
Distances in the Universe
 We can measure distances in the Universe
with 2 units:
 Light-year: It is the distance light travels in
one year. It is 9.5 billion Km
(9.500.000.000.000 Km)
 Astronomical unit (AU): it is the distance from
the Earth to the Sun. It is 150 million Km
(150.000.000 Km)
 AU is the international unit astronomers use