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Chapter 9: Stars and Galaxies

i) The Sun…..

- the centre of our solar system

- The Sun is actually a star of moderate size

- The Sun takes 25 and half days to rotate on its axis

from west to east

Characteristics of

The Sun

Measurement

Size ( diameter) 1.4 million km

Mass 1.989 x 10 kg

Density 1.41 g cm ( compared with density of

water )

Surface temperature 6000 degree Celsius

Temperature of Sun’s

Core

15 million degree Celsius

Table 9.1: Characteristics of the Sun

Notes:

- The Sun’s diameter is 109 times the diameter of the

Earth

- The Sun’s mass is 330 thousand times the mass of the

Earth

- The density of the material that forms the sun is one

over four times that of the Earth

Structure of the Sun…..

The Sun’s atmosphere consists of three parts. The parts are,

i) corona

ii) chromosphere

iii) photosphere

Characteristic of…

Corona…

- outer most layer of gas in the Sun’s atmosphere

- corona forms a circle of white light around the Sun

- only visible during eclipse of the Sun

- temperature is about 1.5 million degree Celsius

Chromosphere…

- bright red layer of gas below the corona

- only visible during eclipse of the Sun just like the

corona

- temperature varies between 10 000 and 500 000 degree

Celsius

Photosphere….

- compact layer of gas seen to be shining with yellow

light from Earth

- Photosphere’s surface appears turbulent because gas from

the Sun’s core is release to its surface

- This layer is responsible for radiating heat and light

from the Sun

Sun’s Core…

- consist of hydrogen and helium gases

- nuclear reaction occurs in the core all the time to

generate and release heat and light energy

- The core’s temperature is extremely high. It’s about 15

million degree Celsius

Photograph 9.2: corona and chromosphere can only be seen

during an eclipse of the Sun

Phenomena of that occur at the Sun’s

atmosphere…

Few of phenomena that occur at the Sun’s atmosphere are

i) prominences

ii) Solar flares

iii) Sunspots

Phenomena Descriptions

Prominence

- an explosion of hot gas that shoots out from

the Sun’s chromosphere with shiny bright

light

- can been seen near the edge of the Sun

during an eclipse of the Sun

- prominence emits charged particles and

ultraviolet rays into outer space

Solar layer

- a strong explosion of gases that happen

suddenly into outer space

- also emit rays like gamma rays and X-rays

- this phenomena occurs for only a few

minutes or a few hours but it release a great

deal of energy

Sunspot - dark spots on the surface of the Sun’s

Photosphere

- has a lower temperature ( 4000 degree

Celsius ) than its surroundings ( 6000 degree

Celsius )

Table 9.2: Description of phenomena of that occur at the Sun’s

atmosphere

The effect of the phenomena on the surface

of the Sun on Earth…

- charged particles as a result of solar flares reach the North Pole or the

South Pole of the Earth and collide with gas molecules in the atmosphere

- as a result, colorful light that consist of green, yellow and red lights are

produced. These light that can be seen at night are called aurora

- the charged particles and radiation from the Sun like cosmic rays, X-rays

and gamma rays will collide with particles in the Earth’s atmosphere

- this causes disturbance to the communications system like television and

radio broadcast, telegraph transmissions and telephone calls.

Generation of energy by the Sun…

- consist of hydrogen and helium gases

- nuclear reaction that takes place in the Sun’s core

generates energy

- during a nuclear reaction, 2 hydrogen atoms fuse to

form one helium atom. Heat and light energy are

released

Stars and Galaxies in the Universe…

Star is…

- a natural object in outer space that can release heat and

light energy

- generates energy through nuclear reactions

Sun is…

- a star that is nearest to Earth

Distance of a star from the Earth is measured in units of

light year, distance traveled by light in a year. There are

bright stars in the sky can been seen by naked eye at night

such as the Sirius and Rigel.

Classification of stars

Stars need to be classified to facilitate research and classified

according to characteristics such as

i) temperature

ii) size

iii) brightness

A star with very lo temperature is red in colour. A star that very hot

is blue in colour.

Dwarf star - very small star, smaller than Earth

Science Corridor:

- Alpha Proxima is the second nearest star to earth. This star is situated about 4.2 light years from Earth- Sirius and Rigel are situated 8.6 and 900 light years respectively from Earth

Giant star - tens of times bigger than the Sun

Supergiant star - very big star, 100 times bigger than the

Sun

Apparent magnitude - measurement of the brightness of object in the

sky that can be seen from Earth. The lower the magnitude value, the

brighter the object

Birth and death of star…

Star - born from nebula

Nebula -

- a large cloud that consist of dust and gases

- gases and particles in the nebula are pulled by strong

gravitational force to form a lump and causes the

lump of gases to shirk and is compressed until it

becomes very compact to form a core

- when temperature and pressure in the core become very

high, nuclear reaction occurs and hydrogen gas is turned

into helium. A lot of heat and light energy are released

the, the core shines and a star is born.

The star will die when all hydrogen gas in its core is used

up in nuclear reaction.

The star will undergo death in by following stages with…

A star of moderate size like Sun:

1. the hydrogen atoms in the star are used up and nuclear

reaction stops

2. the star expands because its gravitational force has

decreased and forms a red giant

3. the outer parts of the star drift out into space leaving

the extremely hot white core called the white dwarf

4. the with dwarf is a star that is dense, compact and

becoming increasingly cold

5. the, its continues to become colder and eventually leaves

a black body or black dwarf (looks dark in outer space)

A star that is bigger than the Sun:

1. the outer layer of the star expands as a result of

decreasing gravitational force to form a red giant

2. it continues to expand and finally explodes as

supernova. A great deal of heat and light energy are

produced

3. very strong gravitational force in the core of the star

converts it into either a neutron star or black hole.

Black hole - an object that is very dense and has strong

gravitational force that pulls all surrounding materials,

including light, that is close by, to it. Black hole also can’t

be seen in outer space.

Neutron star - a very small and dense star as it consist

mainly of neutron particles.

Constellation…

Constellation

- a group of stars that forms a certain pattern

in the sky

- in ancient times, knowledge of the constellation were

used as a calendar and compass

Figure 9.5: Example of constellations

Types of galaxy…

Classified according to:

- elliptical galaxies

- spiral galaxies

- irregular galaxies

Shape of galaxy Example of galaxy

Elliptical Galaxy M87 in Virgo

Spiral Milky Way and Andromeda

Irregular Magellan Cloud

Table 9.3: Shows the shape and example of galaxy

- our solar is in a galaxy called the Milky Way.

- The Sun is one of the millions of stars in the Milky

Way.

iii) Existence of the Universe as a Gift

from God…

Many scientist believe in the theory that the Universe begins

with a huge explosion, the Big Bang. During the explosion,

the Universe expanded from nothing to become a huge space

measuring 2 billion billion kilometers in width, in a single

second.

At present, scientists still can’t explain why the Big

Bang occur. We should appreciate the uniqueness, orderliness,

beauty and harmony in the Universe as a sing Of the glory

of God.

Chapter 10: Space Exploration

Development in the field of astronomy

and space exploration…

Astronomy - is the field of study about natural objects in the

sky

Development in space exploration…

Space exploration is the investigation of the Universe beyond

the atmosphere of the Earth by using spacecraft. Space

exploration was first done from Earth with the use of a

telescope.

Rockets, man-made satellites, space stations and space

shuttles were later invented to continue the efforts of space

exploration.

Year Development

1957 The world’s first artificial satellite, Sputnik 1, was launched. Four months later, Sputnik 2, carrying a dog named Laika was launched

1961 Yuri Gagarin became the first person to orbit the Earth

1969 Man first landed on the Earth

1981 The first reusable names spacecraft, the Space Shuttle, was launched

Table 10.1: Some of the development in space exploration

Application of technology related to pace

exploration and astronomy…

A few types of modern technological instruments have been inverted

for outer space exploration. Among them are the:

- telescope

- spaceship

Telescope are three types of telescope used for outer space

exploration:

- refracting telescope

- reflecting telescope

- radio telescope

Refracting telescope - uses lens while reflecting telescope uses mirrors

to take and send photographs on outer space.

Radio telescope - used to received electric signals and radiation from

outer space.

Spaceships have been launched into outer space to obtain various

information. Spaceships that carry astronauts are launched by rockets

into outer space but probe is a spaceship that doesn’t carry humans.