1. TEMA 2
Adolfo Marquina Rubio 1ºB

2. The stars
• The stars are
huge spheres of
hydrogen and
helium gas.
According to
their colour and
temperature,
they are
classified in
different types:
STAR TEMPERA
TURE
Blue 30.000ºC
White 9.000ºC
Yellow 5.500ºC
Orange 4.000ºC
Red 3.000-
1000ºC

3. Energy of a star
• The life of a star depends on the amount of energy that is
capable of generating at all times. They emit energy due to
nuclear reactions/fusions.
• Nuclear fusion is a reaction in which two simple atoms
come together and combine their nuclei to form a new
atom much more complex.
• In the stars the union of two atoms of hydrogen atoms
forms helium. The stars are in a continuous state of
nuclear fusion.

4. Vital cycle of a star
• Stars are born in galactic nebulae which are composed by
hydrogen and helium. In our galaxy there are many great
nebulae as the Orion nebula and the Trifid nebula.
• Protostar: The contraction of the nebula due to
gravitational attraction produces the formation of
thousands of stellar-mass fragments. The protostars are
formed mainly by hydrogen.

5. Young star
• The hydrogen will become into helium. Then the protostar
will become a star. Nuclear reactions take place in the
center of the star. The energy is released to the surface
keeping the whole star hot. The Sun is currently at this
stage. The Sun is composed by hydrogen (71%), helium (29%)
and other heavier elements (2%).

6. Red Giant Star
• It is the final stage of the life of a star. The structure of
the star has changed. The core is now formed by helium
and nuclear reactions don’t occur in it anymore.
• Nuclear reactions take place in the layer of production
of energy. The increase of density makes the core begin to
shrink and the temperature increases too. The layer of
production of energy becomes denser and the
temperature increases. An acceleration of the nuclear
reactions is produced.
• The production of energy increases the thermal pressure
and radiation pressure increase , both will be greater
than the force of gravity. The star becomes bigger, outer
layers cool down and the star gets red. When the sun
becomes a red giant star it will engulf both Mercury and
Venus, the Earth will be melted.

7. Red Supergiant Star
• Not all the stars end their life as a red giant star. Massive
stars have a more complicated final. During the
contraction of the helium nucleus, temperatures of
100.000.000 degrees are reached. New chains of nuclear
reactions begin. The nuclear fusion of helium is going to
produce carbon and oxygen. The star has two areas of
energy production: the core and the outer layer. The
percentage of energy production is very large, the
pressure increases and the star becomes a red supergiant
star.

8. Cumulus and Galaxies
• Galaxies are huge groups of stars, gas and dust. They
differ by their shapes and sizes and the number of stars
they contain. There are 3 types of galaxy:
• Spiral galaxies: Contain a core and a variable number of
arms
• Elliptical galaxies: They don’t have arms. They consist of
old stars and are the largest galaxies known
• Irregular galaxies: They don’t have definite form and they
are the most abundant. Some of them given their size, are
classified as dwarf galaxies
• The galaxies are grouped to form even larger structures,
called cumulus.
• The Milky Way is part of a cumulus called the “Local
Group”.

9. Nebulae, Quasars and Black Holes
• Nebulae are giant clouds of gas and dust with different
shapes. They are result of big explosions that occur at the
end of the life of massive stars. A massive star is a star
with a mass ten times the mass of the Sun (2x1030
kg).
• Quasars are stellar objects that emit a large amount of
energy as radio waves.
• Black holes are objects in which the light can’t escape
because of their enourmous gravitational attraction.

10. La formación de los Planetas
• Casi toda la materia de la nube que se contrae para
convertirse en una estrella acabará dentro de la propia.
Sin embargo, una pequeña fracción escapará y quedará
girando alrededor de la estrella, se denomina disco
protoplanetario. El material que lo compone es
principalmente hidrógeno molecular y helio. Si el proceso
esta teniendo lugar en una galaxia algo evolucionada
como la nuestra hay también carbono, oxígeno, vapor de
agua, CO2, silicio, hierro, níquel y más elementos en
cantidades menores.
• Las moléculas y los granos de polvo giran alrededor de la
estrella central, se producen interacciones y choques.
Los choques se producen a muy baja velocidad y al chocar
los granos se van uniendo y se forman aglomerados cada
vez más grandes. Todo el material que contenía el disco
protoplanetario pasa a formar los planetas.

11. La formación de los planetas II
• Si el vapor de agua se encuentra lejos de la estrella
central, el agua puede formar cristalitos de hielo que
pueden unirse entre si formando planetas más grandes.
Cerca de la estrella el agua no forma hielo y solo el
polvo y los silicatos participan en los procesos de
agregación formando planetas pqeuqños y rocosos.

12. Los Planetas
• Para medir la distancia de los planetas al Sol se utiliza la
unidad astronómica (para que sobrevivan los cristales de
hielo se necesitan 5) que es la distancia media entre la
tierra y el Sol, unos 150.000.000 de kilómetros.
• A menos de esta distancia se encuentran cuatro planetas
pequeños y rocosos: Mercurio, Venus, la Tierra y Marte.
• Más alejados se encuentran los otros cuatro planetas,
que son gaseosos. Estos planetas son: Júpiter, Saturno,
Urano y Neptuno.

13. Otros astros celestes
• Satélite: Son astros que orbitan alrededor de los
planetas
• Asteroides: Objetos de menor tamaño que los planetas y
los satélites. Destacan el cinturón de asteroides entre
Marte y Júpiter.
• Cometas: Objetos con un núcleo sólido formado
principalmente por agua y amoníaco. Cuando se acercan al
Sol desprenden partículas de gas que forman la cola del
cometa.
• Meteoritos: Fragmentos de planetas, cometas y asteroides
que van a la deriva por el espacio. Pueden caer sobre la
superficie de los planetas y su tamaño varía de unos
gramos a toneladas.