Year 10 Astronomy Revision
Name: _________________________________
1. Arrange the 8 planets in order from the Sun.
1. Mercury 2. Venus 3. Earth 4. Mars 5. Jupiter 6. Saturn 7. Uranus 8. Neptune
2. Which are the 4 Inner Planets and which are the 4 Outer Planets?
Give 3 differences between these 2 types of planets.
THE INNER PLANETS
Mercury, Venus, Earth and Mars
Small size
THE OUTER PLANETS
Jupiter, Saturn, Uranus and Neptune
Huge!
Jupiter, the largest planet, has a diameter of 142,984
Earth is the largest of the Inner Planets, with a diameter of
km (88,846 miles). Neptune is the smallest of the
12,756 km (7,926 miles). Mercury is the smallest with a diameter
Outer Planets with a diameter of 49,532 km (30,779
of 4,878 km (3,031 miles)
miles)
Balls of gas with no surface
Have solid surfaces and thin/no atmospheres
Most of the Outer Planets are made of gas. It is likely
In theory, it would be possible to stand on each of the Inner
that they have a much smaller solid or liquid centre.
Planets, although you would only survive on Earth.
It would be impossible to stand on any of the Outer
Planets.
Greater Density
Smaller Density
The size and composition of the planets is caused by the density
Despite being larger, the elements that make up the
of the elements that make up the planets. The elements in the
Outer Planets are less densely packed together
Inner Planets are more closely packed together, causing them to
causing them to be quite light for their size.
be smaller on solid.
Varied atmospheres
The contents of the atmospheres of the Inner Planets varies from
planet to planet. Mercury has no atmosphere although Sodium
and Helium can be detected above the surface. Venus'
atmosphere is mostly Carbon Dioxide with a very small amount
of Nitrogen. Earth's atmosphere is mostly Nitrogen with a
smaller amount of Oxygen and even smaller amounts of other
gases. Mars has a similar composition of carbon dioxide and
nitrogen as Venus although has a much thinner atmosphere.
Known by the ancients
Similar atmospheres
The atmospheres of the Outer Planets consist mostly
of Hydrogen and Helium, with Methane also being
present in the atmospheres of Uranus and Neptune.
Other gases are present although in much smaller
quantities.
Not known by the ancients
Of the Outer Planets, only Jupiter and Saturn were
The existence of the Inner Planets has been known about for
observed by ancient astronomers. The existence of
thousands of years. The earliest astronomers didn't know that the
Uranus and Neptune was not known until relatively
four objects (including Earth) were planets, but they knew they
recently. Uranus was discovered in 1781 and
existed.
Neptune in 1846.
Spin quickly
Spin slowly
All of the Outer Planets spin quicker than the Inner
Compared to the much larger Outer Planets, the Inner Planets
Planets. Uranus spins slowest, taking 17 hours and 14
spin quite slowly. Earth spins the quickest, taking 23 hours and minutes to spin on its axis. Jupiter takes only 9 hours
56 minutes to spin on its axis. Venus takes 243 days to spin on
and 55 minutes to spin on its axis. This rapid rotation
its axis, spinning in an opposite direction to the other planets.
causes Jupiter and Saturn to appear squashed, wider
across the equator than from top to bottom.
Orbit the Sun slowly
Orbit the Sun quickly
The Outer Planets orbit the Sun from millions of
Because they are quite close to the Sun, the Inner Planets
miles and have a much greater distance to cover to
complete an orbit quickly. Mercury takes only 88 days to orbit
complete an orbit, so take much longer to do so.
the Sun. Mars takes 687 days.
Jupiter takes almost 12 years to complete an orbit and
Neptune takes over 164 years.
Lots of Moons
Few Moons
Only Earth and Mars have moons orbiting them. One moon
orbits Earth and two small moons orbit Mars.
No rings
None of the Inner Planets have rings orbiting them
Multiple space craft visitors
Due to being close to Earth, there have been several missions to
the other Inner Planets, especially to Mars and Venus. Mercury
has been visited by two spacecrafts.
All of the Outer Planets have many moons orbiting
them. There are 63 moons known to orbit Jupiter, 60
orbiting Saturn, 27 orbiting Uranus and 13 orbiting
Neptune.
Rings
All of the Outer Planets have rings orbiting them.
The rings are thin discs of dust and rocks possibly
caused by moons being broken up or not being
completely formed while orbiting the planet. Saturn
has the most visible ring system of any of the planets.
All Outer Planets visited by one space craft
There have been multiple visits to Jupiter and Saturn,
but Uranus and Neptune have only been visited once.
This was by Voyager 2 (which also visited Jupiter
and Saturn).
3. Why Pluto is no longer a Planet (since 2006)?
It occurred during the 2006 International Astronomical Society convention. Pluto was reclassified as a 'Dwarf Planet' because of even larger objects discovered further out from
Pluto. It's thought that up to *50,000* Pluto-sized objects and larger could exist in the
Kuiper belt, so, rather than have to come up with names for that many planets, Pluto's
classification was changed, and it's now the first "Kuiper Belt Object" discovered.
The orbit is not in the same plane as the orbits or other planets.
4. What is the meaning of orbit in astronomy? Give 3 examples of celestial objects that orbit
others.
Orbit means to revolve around another object.
Planets orbit the Sun, comets orbit the Sun, asteroids orbit the Sun, moons orbit planets,
artificial satellites orbit planets, stars can orbit each other (any 3).
5. Arrange these celestial objects according to their size in descending order.
Milky Way, Super-cluster, Universe, Earth, Meteoroid, Jupiter, Sun, Local Group, Mars,
Asteroid, Solar System, our Moon.
Meteoroid  Asteroid  Our Moon  Mars  Earth  Jupiter  Sun  Solar System 
Milky Way Galaxy  Local Group  Super-cluster  Universe
6. What are the 2 opposite
forces the control or maintain
the integrity of a star?
Explain briefly.
Gravitational force as a result
of the mass, pulling the star
inward, against the outward
radiation force from fusion of
hydrogen.
7. Describe briefly the structure of our Sun.
Much like the earth, the Sun has many
different layers that define its structure.
Unlike the earth, the Sun is completely
gaseous, there is no solid surface on the Sun.
Although the Sun is completely made of gas,
the density and temperature of the gas
changes drastically as you travel from the
center to the outermost regions.
8. What is Nuclear Fission in the core of the
Star?
Stars are giant nuclear reactors. In the
center of stars, atoms are taken apart by
tremendous atomic collisions that alter the atomic structure and release an
enormous amount of energy. This makes stars hot and bright.
Stars are powered by nuclear fusion in their cores, mostly converting hydrogen
into helium.
9. What determines the formation of other elements in stars?
A star's mass determines what other type of element undergoing fusion in its
core (or during explosive changes in its life cycle)
a. Small stars: The smallest stars only convert hydrogen into helium.
b. Medium-sized stars (like our Sun): Late in their lives, when the hydrogen
becomes depleted, stars like our Sun can convert helium into oxygen and
carbon.
c. Massive stars (greater than five times the mass of the Sun): When their
hydrogen becomes depleted, high mass stars convert helium atoms into carbon
and oxygen, followed by the fusion of carbon and oxygen into neon, sodium,
magnesium, sulfur and silicon. Later reactions transform these elements into
calcium, iron, nickel, chromium, copper and others. When these old, large
stars with depleted cores supernova, they create heavy elements (all the natural
elements heavier than iron) and spew them into space, forming the basis for
life.
10. Name the 3 main types of Galaxies in the Universe and give an example of each type.
(1) Spiral galaxies get their name from the shape of their disks, in which stars, gas and
dust are concentrated in spiral arms that extend outward from the central nucleus of the
galaxies. Eg. The Milky Way, Andromeda Galaxy
(2) Elliptical galaxies are elliptical in shape, eg. M32, Sagittarius Dwarf Elliptical galaxy.
(3) Irregular galaxies have no particular shape, eg. The Large and Small Magellanic Clouds
11. What is the Big Bang Theory?
 Big-bang theory states that the universe originated sometime between 10 billion and
20 billion years ago from the cataclysmic explosion of a small volume of matter at
extremely high density and temperature.
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The Big Bang theory describes how the Universe began in a rapid expansion about 13.7
billion years ago and has evolved since that time.
The Big Bang theory states that the universe began from an initial point or singularity
which has expanded over billions of years to form the universe as we now know it.
12. What is a LIGHT YEAR? Why is it commonly used in astronomy?
A unit of astronomical distance equivalent to the distance that light travels in one year,
which is 9.46 × 1012 km.
Calculation: Light moves at a velocity of about 300,000 kilometers (km) each second.
No. of second in one year = 365 days x 24 hours x 60 mins x 60 secs = 31,536,000 sec
Distance = Speed x Time = 300,000 x 31,536,000 = 9.46 × 1012 km.
Light Year is used to measure the very far away distance between stars.
Our nearest star (Proxima Centauri) is 4.2 light year away.
Our Milky way is about 100,000–120,000 light-years in diameter which contains
approximately 100–400 billion stars.
13. Why is it difficult to travel to another star?
The nearest star is 4.2 light years away. It will take
If the spacecraft is 1000 km/hour, it will take 80,000 years to reach at a super-speed of
240,000 km/hr.
14. What does E=mc2 stand for?
E = mc2 is perhaps the most famous equation of all time. It stands for E(energy) = Mass
times the Speed of Light (C) squared. What this means is that if you take the mass of an
object and multiply it by the speed of light (2.9 x 10^8 metres per second) you will then
have calculated the amount of energy. As you can see, even a tiny amount of mass when
multiplied by such a huge number (C) yields an incredible amount of energy. Releasing
that energy can do everything from power cities (a nuclear power plant) to destroy them
(a nuclear bomb).
15. What is the common name for all the radiation from the stars and matter in the universe?
List all these radiations in order from long to short wavelengths.
Electromagnetic Radiation
Radiowaves  Microwaves  Infra-red  Visible light
 Ultraviolet  X-ryas  Gamma rays  Cosmic rays
(Roy's Mother Is Visiting Uncle Xavier's Garden for a
Coffee)
16. What is the use of Radio telescope? Why is it more
useful than optical telescope?
An instrument used to detect radio emissions from the
sky, whether from natural celestial objects or from
artificial satellites.
It can detect the star’s size, shape, movement,
temperature, composition and location.
It can detect tiny amounts of energy from vast
distances away, through Earth’s atmosphere and dust
and gases in deep space.
It can be placed on Earth instead of the Hubble Space
Telescope in space.
17. What is a Space Shuttle? What is the use of space shuttles?
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The space shuttle is the "world's first reusable spacecraft," launching like a rocket, orbiting like a
spacecraft, and landing like a plane.
Space shuttles could carry satellites, space probes, and other cargo into orbit around Earth on both
commercial and non-commercial missions.
The space shuttle system was made up of three components:
- Two white solid rocket boosters. They provided 80% of the launch thrust.
- The external orange tank, which provided fuel to the space shuttle main engines during launch.
- The white orbiter. It acted as the crew's home during the flight. The space shuttle normally took as
many as seven astronauts to and from space.
All of the components were reused except for the external fuel tank. It burned up in the atmosphere
after launch.
There were five orbiters in the shuttle program's history: Atlantis, Challenger, Columbia, Discovery
and Endeavour.
The Space Shuttle Challenger disaster occurred on January 28, 1986, when Space Shuttle Challenger
(mission STS-51-L) broke apart 73 seconds into its flight, leading to the deaths of its seven crew
members.
The Space Shuttle Columbia disaster occurred on February 1, 2003, when, shortly before it was
scheduled to conclude its 28th mission, STS-107, the Space Shuttle Columbia disintegrated over
Texas and Louisiana as it reentered Earth's atmosphere, killing all seven crew members.
What Did the Space Shuttle Do?
a. It was used to launch satellites and serve as an orbiting science laboratory.
b. Its crews repaired and improved other spacecraft, such as the Hubble Space Telescope.
c. The shuttle was used for military missions.
d. Finally, the space shuttle was mostly used to work on the International Space Station.
18. How Did the Space Shuttle Launch and Land?
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The space shuttle took off like a rocket.
The solid rocket boosters and the main engines on the orbiter
provided the thrust for launch.
The solid rocket boosters burned for about two minutes.
Then they were dropped from the shuttle and fell into the ocean.
Special boats brought them back so they could be used again.
The shuttle's main engines fired for about another six minutes.
The external tank is dropped when all the fuel was used.
Shortly after this happened the shuttle and crew were in orbit.
The orbiter landed like a glider.
While in orbit it fired its engines to slow down and stop orbiting.
After it re-entered Earth's atmosphere, it glided in for a landing
on a runway.
20. Intrepret the Hertzsprung-Russell diagram:
The diagram shows the various stages of stellar evolution. By far the most prominent feature
is the main sequence stars, which runs from the upper left (hot, luminous stars) to the
bottom right (cool, faint stars) of the diagram. Our Sun is a main sequence star with average
size, medium temperature and luminosity. Similar stars (like our Sun) spend about 90% of
their lives burning hydrogen into helium in their cores.
The giant and supergiant stars lie above the main sequence, and white dwarfs are found
below it. Stars enter this evolutionary stage once they have exhausted the hydrogen fuel in
their cores and have started to burn helium and other heavier elements.
White dwarf stars are the final evolutionary stage of low to intermediate mass stars, and are
found in the bottom left of
the HR diagram. These stars
are very hot but have low
luminosities due to their
small size.
Sun
21. List some tools used for
Space Exploration.
Satellites, Space probes,
Space Shuttle, Hubble Space
Telescope (HST), Other
spacecraft like the Mars
Rover, International Space
Station (ISS), Rocket and
Communication Tools.
NB: Space probes are
spacecraft sending to the
space for a purpose. Satellites are spacecraft that orbiting the Earth for many purposes.