Solar System,

Stars &

Galaxies

Our solar system is made up of thea. Sun b. 9 planetsc. Moonsd. Asteroids, meteoroids, and comets

The sun is the center of the solar system and other planets go around it in the same direction.

The sun is the solar system’s star and it provides heat and light.

Planets

Planets are big objects that go around the sun.

Unlike stars, planets do not produce heat and light. They appear shining in the sky because they reflect the light of the sun.

There are nine planets in our solar system, namely Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto (arranged according to the distance from the Sun.)

Each planet has its own features.

a. Mercury • The nearest planet to the sun.• A very hot planet as it is very close to the sun.• The second smallest planet after Pluto.b. Venus • The nearest planet to earth.• The hottest planet• Covered by thick poisonous yellow clouds.c. Earth • The only planet with living organisms• There are air, warmth and water for plants and

animals to survive.d. Mars • Known as the red planet because it is covered

with fine reddish soil.

e. Jupiter • The largest planet• Spins very fast, takes less than 10 hours for one spin.

f. Saturn• Most beautiful planet. It is surrounded by a spectacular set of rings.

• Each ring is made up of billions of pieces of ice rock

g. Uranus • A blue planet with a thin ring• Has a rocky core covered with layers of gases.

h. Neptune • Also a blue planet similar to Uranus.• Has a small rocky core covered with thick gases that reflect a bluish light.

i. Pluto• the smallest planet in the solar

system• The farthest planet from the sun.• A very cold planet

Each planets has its own moons except for Mercury and Venus.

All the planets together with their moons go around the Sun in their own path called orbits which are ellipses.

The powerful gravity of the sun keeps the planets in order.

The further the planet from the sun, the bigger its orbits is. Pluto has the biggest orbit and Mercury has smallest orbit.

Therefore, the planets have different length of years. One planet’s year is the time needed by the planet to make a complete orbit.

As each planet orbits the Sun, it also spins like a top. The planet’s day is the time it takes to spin around once.

Planet Number of moon

Distance from the

Sun(million

km)

Time taken for one orbit

Mercury - 58 88 Earth days

Venus - 108 225 Earth days

Earth 1 150 365 ¼ Earth days

Mars 2 230 687 Earth days

Jupiter 16 780 119 Earth years

Saturn 20 1470 29.5 Earth years

Uranus 15 2870 84 Earth years

Neptune 8 4500 165 Earth years

Pluto 1 6000 248 Earth years

Every planet spin on its axis from west to east except for Venus and Uranus.

Venus spins from east to west.

The axis in which Uranus spins is titled right over. Therefore, Uranus spins from top to bottom like a wheel.

From its discovery in 1930 until 2006, Pluto was demoted in our Solar System. In August 2006, Pluto was demoted as it did not fulfill the latest criteria for the new definition of the word “planet”.

Asteroids, Comets and Meteoroids

Asteroids

Asteroids are small rocks similar to the material that formed the planets. They orbit the sun too.

Most asteroids are located between the orbits of Mars and Jupiter called asteroids belt.

Comets

A comet us composed of dust and rock particles mixed in with frozen water, methane and ammonia.

A comet circles the Sun in a very big elliptical orbit.

Some comets take thousands of years to orbit the Sun.

The most popular comet is Halley’s comet which takes 76 years to orbit the Sun.

When a comet’s orbit take it close the Sun, the heat from the Sun melts some of the ice. This creates a hazy cloud that looks like a gigantic tail

Halley’s Comet

Meteoroids

Meteoroids are small rocky fragment of debris floating through the space.

When the meteoroids float too near to Earth, they will be pulled in by the force of Earth’s gravity.

Most of the meteoroids are so small that they are completely vaporized in Earth’s atmosphere.

A meteoroids that burns up in Earth’s atmosphere is called meteor, or commonly known as shooting star.

If a meteoroids is large enough, it may not completely burn up in the atmosphere. When it hits Earth, its is called meteorite.

When a meteorite strikes on the surface of the moon or planet, a hole is formed, called crater.

1. The Sun is a star located at the center of our Solar System.

2. It is our nearest star and the engine for all life on Earth.

3. The Sun contains 99.85% of all matter in the Solar System.

The Sun

Characteristics of the Sun

4. Our Sun is a medium-sized yellow star.

5. It is a huge, rotating ball of hot gas with nuclear reactions that lights up the Earth and provides us with heat energy.

6. It is formed 4.5 billion years ago.

7. The characteristics of the Sun is the summarized in the table below.

Distance from the Earth 149 680 000 km

Temperature of the Sun The surface temperature is approximately 5500 ◦C. The

outer atmosphere of the Sun is extremely hot, up to 1.5 to 2

million degrees.

Composition of the Sun Composed of about 76% hydrogen and 22% helium. Iron, nickel, silicon and carbon make up the remaining 2% by mass.

Radius (size) 109 times that of the Earth

Density 0.27 times that of the Earth

Mass 330 420 times that of the Earth

The Sun has a four – part structure, from the inner core to the outer corona. Each layer has its own characteristics such as its temperature and density.

Core

The center of the Sun is gaseous core. This is where the nuclear reactions occur. The reactions produce a vast amount of energy. The temperature at the core is about 15, 000,000 C.

The Structure of the Sun

Photosphere

(a) Photosphere is the visible surface of the Sun where the Sun’s energy is seen as moving like boiling water.

(b) Photosphere produces the visible light we see and is generally considered to be the surface of the Sun.

(c) It is one of the coolest layers of the Sun with temperatures less than 6000◦C.

(d) Large magnetic disturbance sometimes break through he photosphere and cause sunspots.

Chromosphere

(a) Just above the photosphere lies the chromosphere, a red-glowing region of gas. It is considered to be part of the solar atmospehere.

(b) The temperature at the chromosphere is about 15 000◦C

(c) The chromosphere is active with activity, mainly due to the various magnetic fields. This causes various phenomena such as sunspots, flares and prominences.

(d) The chromosphere can be seen by the naked eye during a total solar eclipse.

Corona

(a) Above the chromosphere is the outermost, tenuous atmosphere of the Sun, the corona.

(b) The corona is extremely hot. It has a temperature of about 2 000 000◦C.

(c) Prominences can remain relatively quiet and stable for days and weeks, but when the magnetic fields that support them change, they tend to erupt.

Total solar eclipse

1. The Sun might look like an unchanging object in the sky, yet many activities take place in it.

2. The Sun’s magnetic field controls the motion of the gases in the corona, creating delicate streamers which is seen from the Earth as flares and arching prominences.

3. Solar flares

(a) Solar flare is the explosive event in the solar surface. It is the huge outburst of solar material which are several thousand to million kilometers long.

Phenomena occurring at the surface of the Sun

(b) A flare may release an amount of energy equivalent to 100 million hydrogen bombs.

4. Prominences

(a) Prominences are the masses of glowing gas above the Sun’s bright surface. They are visible to the naked eye only during total solar eclipses.

(b) They are suspended above the surface of the Sun by loops of magnetic fields.

(c) Prominences can remain relatively quiet and stable for days or weeks but when the magnetic fields that support them change, they tend to erupt.

(d) Prominences are thousands to million of kilometers wide and tall.

5. Sunspots

(a) If we view the Sun’s image projected by telescope, we will see one or more darker patches which are known as sunspots.

(b) The spots are not genuinely black. They appear so because they are cooler than the surrounding regions of the photosphere.

.

(c) Spots generally appear in groups. Sunspots may be huge, but they are not permanent.

(d) A major group of sunspots may last for six months but the very small spots often have lifetimes of less than a couple of hours

6. Solar wind is a flow of gases from the Sun that disturbs and shakes the Earth’s magnetic field.

7. Solar flares often give off ultraviolet light and X-ray that heat up the Earth’s upper atmosphere. This “space weather” can change the orbits of the satellites and shorten their lifetime.

8. The excessive radiation can physically damage the satellites and pose a threat to astronauts. When the Earth’s magnetic field is disturbed, it can also result in current surges in power lines that destroy equipment and knock out power over large areas.

9. Researchers suspect that long-term changes is solar radiation cause substantial variations in the global climate.

For example, scientists have found a correlation between low sunspot activity and severe Ethiopian droughts that occurred over a period or more than four centuries.

1. Looking at the Sun improperly can harm your eyes. Never watch the Sun with a telescope or binoculars because the concentrated light will turn your retina. Even staring at the Sun for more than a couple of seconds can damage your eyes.

Amazing Facts

2. Those who live at far northern and southern latitudes on the Earth may occasionally observe a spectacular light show in the sky that is caused by solar wind. Solar flares not only emit radiation such as X-rays but also atomic particles. When the strong solar wind distorts the Earth’s magnetic field, it affects the motion of charged particles. These particles crash into the upper atmosphere, exciting the gas atoms there and causing them to glow. The glow can be seen from the ground as aurora.

Aurora – a phenomenon caused by solar wind

1. The Sun generates its energy by a nuclear reaction called nuclear fusion.

2. The Sun is a powerful fusion reactor.

3. Fusion occurs at the center of the Sun.

4. At the Sun’s core, hydrogen atoms bang into each other constantly and fuse into atoms of helium.

5. Energy is released when the nuclear reactions inside the Sun convert hydrogen to helium.

Generation of energy by the Sun

7. Every second, the sun converts about 4 million tons of hydrogen to helium and energy and radiates it into space.

8. The Earth only intercepts one billionth of the Sun’s light energy.

6. During the fusion process, a small amount of energy mass is converted to a large amount of energy.

Stars and Galaxies

Star

A star is a self- luminous gaseous body.

The Sun is an example of a star. It is a self-luminous sphere of gas and plasma that is held together by its own gravity and energized by nuclear reactions in its interior.

Stars come in different sizes.

Type Size (relative to the diameter of the Sun

Supergiant 100 to 1000 times bigger

Giant 10 to 100 times bigger

White dwarf 1000 times smaller

Types of Stars according to sizes

Stars also vary in brightness and colour according to their approximate surface temperature.

Sirius and Rigel are examples of bright stars.

Classification of Stars

Colour Temperature Example

Blue > 25, 000 Spica

Bluish- white 11,000 – 25, 000 Rigel

White 7500 – 11, 000 Vega

Yellowish- white 6, 000 – 7, 500 Capella

Yellow 5, 000 – 6, 000 Sun

Orange 3, 500 – 5, 000 Arcturus

Red < 3,500 Antares

Constellation

Constellation is a group of stars with a pattern of maybe an animal or a familiar object.

Most of the constellations were named after animals or characters in ancient mythology.

Up to date, modern astronomers had named 88 constellations.

Locating stars and constellations sky is fascilitated by a star map it varies depending on the season.

In order to use the star map effectively, you need to know your latitude and longitude on the surface of the Earth, and also the offset of your timezone from Greenwich meridian.

The signs of zodiac are Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Sagittarius, Capricornus, Aquarius and Pisces.

Formation of Stars

Stars are formed from nebulae.

Nebulae are clouds of gas and dust. They glow by reflecting the light of nearby stars. Nebulae are regarded as regions in which fresh stars are being formed out of the interstellar material.

A star is born when enormous clouds of dust and gas in a nebula collapse under the force of the gravity.

The collapse causes the cloud to spin progressively faster and condenses the material that makes up a nebula.

As these material is condensed and compressed by the gravitational force, its temperature begins to rise at its centre.

When the temperature has risen sufficiently, nuclear fusion occurs in the core and energy in the form of heat and light travels out from the centre. It glows and turns into a star.

As long as there is still material within the star, the nuclear fusion process can continue and the star will continue to glow.

Death of Stars

The destruction of a star begins when it has used up its core hydrogen fuel.

The core will shrink and heat up, whereas the outer layers will expand and cool.

During this time, the star will turn into a red giant. It is tens or even hundreds of times larger than before.

For a medium- sized star like our Sun, its outer layers will disperse into space. The core that is left will become a white dwarf.

Giant stars will expand further to become supergiants and blow up in a supernova explosion. The star will end up as a neutron star.

For the very big stars, however they will become black holes.

The gravity around a black hole is so strong that absolutely nothing, not even light, can escape.

Galaxies

The universe consists of everything that exists around us. All matter and energy are part of the universe.

There are millions of galaxies in our universe.

A galaxy is a system of stars. It is like an island in space made up of gas, dust and millions of stars.

SpiralIrregularElliptical

Our solar system is located in the Milky Way galaxy.

Milky Way is a fairly large spiral galaxy. It consists of about 200 billion stars with our own Sun being one of them.

Galaxies come in various shapes, they can be spiral, elliptical or irregular.

The existence of the Universe

We should be thankful for the existence of the universe and appreciate the uniqueness, order, beauty and harmony of the universe as a gift from God.

The universe is so vast, nobody has seen the edge of it. The Earth is less than a speck of dust in the universe.

All that exists in the universe is not permanent. Therefore, we should value our life and make it meaningful.

The importance of the Sun to life on Earth

There could be no life on Earth without the Sun.

The Sun is a source of light and heat for life on earth.

Plants transform solar energy into chemical energy stored in food through a process called photosynthesis. Therefore, the Sun is that the bottom of all food chains.

Modern humans use energy from the Sun as a clean, inexpensive source of power in the form of solar energy.

The Sun also serves as an important role in helping us to understand the rest of the universe. It is the only star close enough to us and serves as the key in understanding other stars.

The importance of the Moon to life on Earth

The Earth has a large satellite which is called the Moon.

The Moon is directly or indirectly influencing the life on Earth.

The most obvious influence of the Moon on the Earth is the ocean tides.

The regular rise and fall of sea level creates a unique environment for life on Earth.

The Moon has also encourage the development of intelligence of humans, specially in mathematics, arts and sciences.

By observing changes in the Moon’s phase and brightness, humans have developed the calendars. It helps them to plan their life accordingly.

When Galileo turned his telescope towards the Moon, it spurred the high technological development in space exploration.