UNIT 1. UNIVERSE AND SOLAR SYSTEM

1. COMPOSITION AND ORIGIN OF THE UNIVERSE.

The Universe consists of a large numbers of galaxies joined in galaxy clusters. Galaxies are a vast collection of stars, dust and gases. Our galaxy is the Milky Way.

Stars are formed when clouds of gases pull together by gravitational forces. They are so hot inside that they emit heat and light. A galaxy can have up to three hundred thousand million stars. The stars you see at night do not seem very bright because they are much further away than the Sun.

The majority of the stars have got planets rotating around them. They form planetary systems. Planets do not emit light, but you can sometimes see planets in the night sky. This happens because they reflect light from the Sun. Sometimes planets look brighter than stars because they are much closer to the Earth. Our planetary system is the Solar System. It is made up of eight planets and one star, the Sun, as well as moons, comets and asteroids.

Some planets have got natural satellites rotating around them. The Earth’s satellite is the Moon.

The origin of the universe is the Big Bang, a big explosion that happened fifteen thousand million years ago.

2. LOCATION OF THE SOLAR SYSTEM WITHIN OUR GALAXYThe Solar System is located in the Milky Way galaxy, a barred spiral galaxy. Our Sun resides in one of the Milky Way's outer spiral arms.

3. HOW BIG IS THE UNIVERSE?WHAT UNIT OF MEASUREMENT DO ASTRONOMERS USE?

Astronomical unit (AU) is the distance between the Earth and the Sun= 150 million kilometres.Express the distance of Mercury, Mars and Pluto from the Sun in kilometres:

Mercury: 0,4 AU = 0,4 x 150.000.000 = 60.000.000 Km Mars: 1,5 AU = 1,5 x 150.000.000 = 225.000.000 Km Pluto: 39,4 AU=39,4 x 150.000.000 = 5.910.000.000 Km Light year. It is the distance light travels in a year. Light travels 300,000 km per second. The nearest

star to the Sun is called Proxima Centauri. It is 4.22 light year away.

4. SOLAR SYSTEM

The Solar system consists of the Sun, 8 planets, dwarf planets and other small bodies such as asteroids, comets and satellites.

The Sun consists mainly of two gases: hydrogen and helium.

Planets are spherical bodies which revolve around the Sun. They move in elliptical orbits.

There are 8 planets in our Solar System: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.

The four inner or terrestrial planets (Mercury, Venus, Earth and Mars) have dense rocky compositions, few or no moons, and no ring systems.

The four outer planets (Jupiter, Saturn, Uranus and Neptune) are also called gas giants as they are bigger and also made up mainly of gases.

Mercury is the closest planet to the Sun and also the smallest. It has no natural satellites. Venus is close in size to Earth. It has an extremely dense atmosphere which consists mainly of carbon

dioxide (CO2). This thick atmosphere makes it the hottest planet of the system, with surface temperatures over 400°C. Venus has no natural satellites.

Earth is the largest and densest of the inner planets and the only planet known to have life. Its liquid hydrosphere is unique among the inner planets. Earth's atmosphere has been altered by the presence of life to contain 21% free oxygen. It has one satellite, the Moon.

Mars is smaller than Earth and Venus. It has a tenuous carbon dioxide atmosphere. Mars has two tiny natural satellites (Deimos and Phobos).

Between the orbits of Mars and Jupiter is located the Main Asteroid Belt. Asteroids are rocky bodies that range in size from hundreds of kilometres across to microscopic.

Jupiter is the largest planet of the Solar System. It is composed largely of hydrogen and helium. Jupiter has more than 60 known satellites. The four largest are Ganymede, Callisto, Io, and Europa. These satellites show similarities to the inner terrestrial planets, such as volcanism and internal heating.

Saturn, famous for its extensive ring system, has similarities to Jupiter, such as its atmospheric composition. Saturn has 62 known satellites. The largest one is Titan.

Uranus is the lightest of the outer planets. Uniquely among the planets its axial tilt is over ninety degrees to the ecliptic. Uranus has twenty-seven known satellites.

Neptune, though slightly smaller than Uranus, is much denser. Neptune has thirteen known satellites. The largest one is Triton, with a retrograde orbit.

Dwarf planets are spherical celestial bodies, smaller than planets, which have not cleared its neighbouring region of planetesimals. Pluto, Eris, Ceres, Makemake are some of the Solar system’s dwarf planets. When Pluto was discovered in 1930 it was considered to be the ninth planet. This changed in 2006 with the adoption of a formal definition of planet. Pluto has a relatively eccentric orbit.

Comets are small Solar System bodies composed largely of volatile ices and fragments of rock. When a comet enters the inner Solar System, its proximity to the Sun causes its icy surface to sublimate and ionise, creating a coma: a long tail of gas and dust often visible to the naked eye.

Short-period comets, such as Halley's Comet, are believed to originate in the Kuiper belt, while long-period comets, such as Hale-Bopp, are believed to originate in the Oort cloud.

The Kuiper belt, the region's first formation, is similar to the asteroid belt, but composed mainly of ice. It is composed mainly of small Solar System bodies, but many of the largest Kuiper belt objects may be reclassified as dwarf planets. Pluto is the largest known object in the Kuiper belt.

The hypothetical Oort cloud is a great mass of up to a trillion icy objects that is believed to be the source for all long-period comets and to surround the Solar System.

5. THE UNIVERSE. OLD IDEAS.

Geocentric theory. In the second century before Christ, Ptolomy proposed this theory claiming that the Earth was quiet in the middle of the Universe and the Sun, planets, stars and the Moon were rotating around it.

Heliocentric Theory. In 1542, Nicolaus Copernicus stated that it was the Sun that was quiet and the planets rotated around it. This theory was supported by Galileo Galilei using one of the first telescopes.

Activities:1. Write down the names of the inner planets, starting with the one closest to the Sun.2. Name the planets that are made of gas.3. What is a star?4. Why does the Sun look much brighter than other stars?5. Why do planets look like stars in the night sky?6. Which of the planets is more similar to the Earth in:

a. Its distance from the Sun.b. The number of moons it has.c. Its size.

7. Imagine that Betelgeuse, a star located 600 light years away from the Earth explodes next month, ¿when will it be possible to be seen from our planet?

8. Does a light year measure distance or time?9. How many astronomical units are in a light year?10. In 1961, the astronomer Frank Duke calculated that approximately half of the stars in our galaxy

may have planetary systems.a. How many stars does our galaxy have?b. Therefore, how many planetary systems may be in the Milky Way?

c. If only one every one hundred planetary systems had a planet with similar size and distance to its stars as the Earth has, how many planets with similarities to the Earth may be in our galaxy?

11. Look at the table bellow and answer the following questions:

PlanetDistance from the Sun (million km)

Mean surface temperature (ºC)

Time for the rotation of its axis

(hours)

Time for one orbit around the Sun

Mercury 58 170 1400 88 daysVenus 108 460 5800 225 daysEarth 150 15 24 365 daysMars 228 -50 25 687 days

Jupiter 778 -143 9.8 12 yearsSaturn 1427 -195 10.2 29 yearsUranus 2870 -201 17 84 years

Neptune 4497 -220 16 165 years

a. Draw a bar chart showing the relation between the distance from the Sun and the mean temperature of each planet.

b. Describe the pattern you can see from your graph.c. The asteroids are about 400 million km. from the Sun. Use your graph to estimate the mean

temperature on an asteroid.d. One planet does not fit the pattern on the graph. Find out why this planet does not follow

the pattern.e. Explain why there could be no liquid water on the surface of:

i. Marsii. Venus

f. On which planet would the time between sunrise and sunset be shortest?g. Which planet has the shortest year?

12. Copy and complete the sentences. Use these words:

gravity planets strongest moons Sun cold Venus Mercury Neptune

The Solar System is made up of in orbit round the Sun. Most of the planets have in orbit round them. They are held in orbit by the force of . The biggest planets have the gravity.

The planets are at different distances from the . The closest one is and the furthest away is . Planets which are a long way from the energy of the Sun are and dark. The hottest planet is and the coldest is Neptune.

13. Connect the start of each sentence to its most suitable ending.

The Earth is a … … star.The Sun is a … … Moon.The Earth is smaller than the … … planet.The Earth is larger than the … … sphere.The Sun, Earth and Moon are each shaped like a … … Sun

14. Write these things in order, starting with the smallest and ending with the largest:

Earth Universe Moon Sun Asteroid Solar System Galaxy

15. Complete the following crosswords.

16. Read the texts and answer the questions:

17. Draw a path that joins each small Solar System body with its characteristics:

ASTEROIDS DWARF PLANETS COMETS

Made up of rocks and metalsEros, Pluto and Ceris are three of

themMade up of dust and ice

Spherical bodiesMost orbit the Sun in an area

between Mars and JupiterForm tails when they pass through

the inner Solar System

They are irregular in shape Smaller than planets They have a centre called nucleus

They can be from a few meters to several hundreds meters wide

They orbit the Sun in the Oort Cloud

Their orbit has a different inclination compared to planets´

orbit.They lose matter when they pass

close to the SunThey orbit the Sun in an area called

belt.They orbit the Sun in different

places

COMETS ASTEROIDS DWARF PLANETS

6. CONSTELLATIONS AND STARS COUNTER

A star is a body made of hydrogen and helium that gives out light.

Ancient peoples looked up into the night sky and saw pictures in the stars. A constellation is a group of stars that creates recognizable patterns in the sky. When one draws imaginary lines connecting the star patterns together, they form shapes that are named after animals and mythological characters.

Many centuries ago, people used the constellations to navigate and the star patterns helped them find the correct navigational stars. Astronomers identify 88 different constellations found in eight different star families.

About 8000 stars were possible to be seen from the Earth some centuries ago. Nowadays, we can’t see more than 2000 stars at the same time in each Hemisphere. This is due to the smog and the light pollution. Have you ever count the number of stars you see at night? Of course, it’s impossible to count every star in the night sky, but you can get very close to the actual number with a simple instrument: a stars counter.

What do we need to make it?

A card. A compass. A piece of string (40 cm.)

A ruler Scissors

How can we make it?

Using your compass, make a circle with a 6 cm. radius in your card. Cut out the circle with your scissors. Behind the big circle, make a small one and tie the string to it. The piece of string must be 30 cm. long, so use the ruler to measure

the string and cur it. You can decorate your star counter as you wish.

How does it work?

At night, put your stars counter close to the window.Take the free end of the string and put it near your face. Now you’ll be 30 cm away from the big circle

and therefore you are seeing 1% of the sky above you.Count the number of stars you can see.Now, change the position of your stars counter and count the number of stars again. Do the same

several times and complete the next table:

OBSERVATIONS NUMBER OF STARS

Observation number 1, zone 1

Observation number 2, zone 2

Observation number 3, zone 3

Observation number 4, zone 4

Observation number 5, zone 5

Observation number 6, zone 6

Observation number 7, zone 7

Observation number 8, zone 8

Observation number 9, zone 9

Observation number 10, zone 10

TOTAL NUMBER OF STARS

Finally, you have to do the next operation:

If you want to, you can give your data to the NASA. Try it through this web page:http://www.nasa.gov/audience/foreducators/son/energy/starcount/index.html

Activities:

18. What’s a star?

19. What’s a star made of?

20. How many stars can we see from the Earth?

21. What’s a constellation?

22. How many constellations are identified? Name two of them.

23. Complete the chart with the words below: