............................ The Universe, the Milk Way and the Solar System

Introduction. The observation of the next sky at night, without clouds or lights, generally provoke us fascination, an increasing feeling when we deepen the knowledge in this subject. We can distinguish many "stars", but some in fact are far away galaxies, that is to say, a large group of stars with enormous clouds of gas and cosmic dust, that moves throughout the space. The small galaxies "only" have about 100 thousands stars, whereas the biggest galaxies may have more than 3 billion (3 ·1012).

Our star, the Sun, is only one more star and the volume of our planet, which seems so big to us, is a million times smaller than the Sun. It is evident that if we do not know something of the Universe practically we are unaware of almost everything that exists. That is why it is very important to study it, and also because may be a day the human beings will be able to travel to other points of the Universe. In this chapter you will find very interesting data about the Universe and our Solar System.

Activities to carry out. Read the explanations about the Universe, the stars, the galaxies and the Milk Way and answer the questions of the "Test of multiple answers 1.1". Afterwards you read the explanations on the Solar System, the planets, the satellites and the comets and answer the questions of the "Test of multiple answer 1.2" and the "Crossword 2"

1. Universe. It is the complex of all the matter that exists. It has been proved that the Universe is in continuous expansion. According to the theory of "the great explosion" (Big Bang), 15 000 million years ago all the matter and energy were found concentrated in only one point that exploded.

2. Astro o celestial body. It is each mass of matter that there is in the Universe. There are many types of celestial bodies, the main ones are the stars, the planets and the satellites. .

3. Star. It is a celestial body with its own light. It has a gaseous nature and occur in its interior atomic reactions in which is apparent heat energy and very bright. An example of star is the Sun.

4. Classification of the stars. The stars are classified according to its temperature and size.

1.) According to the temperature of its surface the stars are classified in: reds (3.000º C), yellow (6.000º C), white (8.000º C) and blue (about 50.000 º C).

2.) According to the size the stars oscillate among a size as that of our planet (dwarf stars) size up to one 1000 times bigger that the Sun (supergiant stars). .

5. The evolution of the stars. The young stars are formed by condensation of atoms of hydrogen and a small fraction of atoms of other types (cosmic dust), that together form the nebula. The hydrogen atoms react between them originating helium, which accumulates in the nucleus, and energy. The hydrogen surface expands and radiates red light originating a red giant star. In its nucleus the helium is converted into other chemical elements and, finally, as its mass is higher or lower, it will form a white dwarf, a neutron star or a black hole. Sometimes the star collapses and explodes originating a supernova.

6. Galaxy. It is a cluster of stars, cosmic dust and gas that moves through space. 100,000 galaxies are known. Each one may contain between 100,000 to 3 billion stars. An example is the Milky Way galaxy.

7. Type of galaxies are named by their shape: elliptic (1) spiral (2), barred (3), irregular or spheroidal.

Types of galaxies

8. Light year. It is the distance traveled by light in a year. Since light moves at 300,000 km / s is an enormous length. Is used to express the distance between the stars.

9. Milk Way. It is the galaxy in which our solar system is located. It is composed of about 100,000 million stars. It is a spiral galaxy type and has four arms. In one of them is the Sun. This is why, at night is observed milky spot and extended (way of milk). It has a diameter of 100,000 light years and a thickness in the center of 20 000 light years. One of the closest galaxies to it is the Andromeda galaxy that is 2 million light years away.

Milk Way

10. Nebula. It is a mass of cosmic dust and gas that is illuminated by the stars.

11. Planet. It is an opaque celestial body, is to say without light itself, which revolves around a star that is sufficiently large to generate a gravitational force that attracts all the other bodies in orbit. An example is the planet Earth.

12. Dwarf planet. It is an opaque celestial body, is to say without light itself, which revolves around a star that not have a sufficient size to generate a gravity able to attract other bodies of the same orbit. Makes a size between 700 and 2500 km in diameter. An example of a dwarf planet is Pluto.

13. Satellite. It is an opaque celestial body that revolves around a planet. Examples of satellites are the moon, which revolves around the Earth, and Phobos and Deimos orbiting Mars.

14. Constellation. Sky region delimited by a group of stars that appear to move together. The main constellations are known since early civilizations and received mythological names. For example Ursa Major, Ursa Minor, Orion, etcetera. The 12 constellations that are seen near the horizon and that the Earth is apparently around the Sun are called Zodiacal Constellations.

Multiple choice Test 1.1

(Spanish activity. Activity in English is under construction)

14. Solar System. It is the set of opaque celestial bodies orbiting a star. An example is our solar system, it is where the planet Earth is located. It is constitued by a star called Sol, 8 planets, 3 dwarf planets, 61 satellites and a lot of asteroids and meteoroids.

15. Planets of our Solar System. From high to low proximity to the Sun the 9 planets are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. According to their characteristics it is possible to distinguish between two types:

  • The four inner and dense planets. The planets are the closest ones to the Sun They have an internal structure similar to Earth, that is made of rocks, therefore are called terrestrial planets or telluric planets . The planets are: Mercury, Venus, Earth and Mars.
  • The four outer and light planets. They are the most distant from the Sun They have an internal structure similar to Jupiter, which basically consists of hydrogen and helium, therefore are called planets Jovians. The planets are: Jupiter, Saturn, Uranus and Neptune.

16. Dwarf planets of our solar system. From high to low proximity to the Sun the 3 dwarf planets are: Ceres, which is in the so-called "asteroid belt" that is between Mars and Jupiter; Pluto, that is farther away Neptune, and Eris that is the latest celestial body of Solar System. Eris and Pluto revolve around the Sun in different planes of the planets.

Solar system

17. Movement of the planets. The nine planets present two types of movements:

  • Rotational motion. Is the rotation about its own axis. Each turn is called day.
  • Translational movement. Is the rotation around the sun is called each year round.

18. Asteroid. It is an opaque celestial body, usually rocky that orbits the Sun and has a dimension greater than a meteoroid but smaller than a minor planet, ie between 50 and 700 km in diameter. 94% of these move in orbits located between Mars and Jupiter, forming the so-called asteroid belt. These are remnants of matter of the solar system that did not become a planet.

19. Meteoroid. It is a celestial body that orbits the Sun and the size of which varies between the molecules that make up the space dust and 50 km in diameter. If they turn and go through the Earth's atmosphere, the friction with the air causes them to become incandescents and create a bright vapor trail called shooting star. The smallest decay before reaching the Earth's surface, but the greatest impact and reach are called meteorites.

20. Comet. It is a small celestial body that makes a highly eccentric and extended orbit _ and is only visible when it passes near the Sun. The solar heat makes the comet's surface of ice to evaporate and raises the comet dust, forming a long illuminated hair, the so-called comet tail.

Multiple choice Test 1.2 (Spanish activity. Activity in English is under construction)
Crossword 1 (Spanish activity. Activity in English is under construction)

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