The Sun or Sol, is the star at the centre of our solar
system and is responsible for the Earth’s climate and
weather. The Sun is an almost perfect sphere with a
difference of just 10km in diameter between the
poles and the equator. The average radius of the Sun
is 695,508 km (109.2 x that of the Earth) of which 20–
25% is the core.
Star Profile
Age: 4.6 Billion Years
Type: Yellow Dwarf (G2V)
Diameter: 1,392,684 km
Circumference at Equator: 4,370,005.6 km
Mass: 1,989,100,000,000,000,000,000 billion kg
(333,060 x Earth)
Surface Temperature: 5500 °C
Size Of The Sun
Facts About The Sun
One million Earths could fit inside the Sun:
If a hollow Sun was filled up with spherical Earths
then around 960,000 would fit inside. On the other
hand if these Earths were squished inside with no
wasted space then around 1,300,000 would fit inside.
The Sun’s surface area is 11,990 times that of the
Earth’s.
Eventually, the Sun will consume the Earth:
When all the Hydrogen has been burned, the Sun will
continue for about 130 million more years, burning
Helium, during which time it will expand to the point
that it will engulf Mercury and Venus and the Earth.
At this stage it will have become a red giant
The Sun will one day be about the size of Earth:
After its red giant phase, the Sun will collapse,
retaining its enormous mass, but containing the
approximate volume of our planet. When this
happens, it will be called a white dwarf.
The Sun contains 99.86% of the mass in the Solar
System:
The mass of the Sun is approximately 330,000 times
greater than that of Earth. It is almost three quarters
Hydrogen, whilst most of the remaining mass is
Helium.
The Sun is an almost perfect sphere:
There is only a 10 kilometre difference in its polar
diameter compared to its equatorial diameter.
Considering the vast expanse of the Sun, this means
it is the closest thing to a perfect sphere that has
been observed in nature.
Light from the Sun takes eight minutes to reach
Earth:
With a mean average distance of 150 million
kilometres from Earth and with light travelling at
300,000 kilometres per second, dividing one by the
other gives us an approximate time of 500 seconds,
or eight minutes and 20 seconds. Although this
energy reaches Earth in a few minutes, it will already
have taken millions of years to travel from the Sun’s
core to its surface.
The Sun travels at 220 kilometres per second:
The Sun is 24,000-26,000 light years from the galactic
centre and it takes the Sun 225-250 million years to
complete an orbit of the centre of the Milky Way.
The distance from the Sun to Earth changes
throughout the year:
Because the Earth travels on an elliptical orbit around
the Sun, the distance between the two bodies varies
from 147 to 152 million kilometres. The distance
between the Earth and the Sun is called an
Astronomical Unit (AU).
The Sun is middle-aged:
At around 4.5 billion years old, the Sun has already
burned off about half of its store of Hydrogen. It has
enough left to continue to burn Hydrogen for
approximately another 5 billion years. The Sun is
currently a type of star known as a Yellow Dwarf
The Sun has a very strong magnetic field:
Solar flares occur when magnetic energy is released
by the Sun during magnetic storms, which we see as
sunspots. In sunspots, the magnetic lines are twisted
and they spin, much like a tornado would on Earth.
The temperature inside the Sun can reach 15
million degrees Celsius:
At the Sun’s core, energy is generated by nuclear
fusion, as Hydrogen converts to Helium. Because hot
objects generally expand, the Sun would explode like
a giant bomb if it weren’t for its enormous
gravitational force.
The Sun generates solar wind:
This is a stream of charged particles, which travels
through the Solar System at approximately 450
kilometres per second. Solar wind occurs where the
magnetic field of the Sun extends into space instead
of following its surface.

MERCURY FACTS
Mercury is the closest planet to the Sun and due to
its proximity it is not easily seen except during
twilight. For every two orbits of the Sun, Mercury
completes three rotations about its axis and up until
1965 it was thought that the same side of Mercury
constantly faced the Sun. Thirteen times a century
Mercury can be observed from the Earth passing
across the face of the Sun in an event called a transit,
the next will occur on the 9th May 2016.
Planet Profile
Mass: 330,104,000,000,000 billion kg (0.055 x Earth)
Equatorial Diameter: 4,879
Polar Diameter: 4,879
Equatorial Circumference: 15,329 km
Known Moons: none
Notable Moons: none
Orbit Distance: 57,909,227 km (0.39 AU)
Orbit Period: 87.97 Earth days
Surface Temperature: -173 to 427°C
First Record: 14th century BC
Recorded By: Assyrian astronomers
Size Of Mercury Compared To The Earth
Facts About Mercury
A year in Mercury is just 88 days long:
One day on Mercury lasts the equivalent of 176 Earth
days. Mercury is nearly tidally locked to the Sun and
over time this has slowed the rotation of the planet
to almost match its orbit around the Sun. Mercury
also has the highest orbital eccentricity of all the
planets with its distance from the Sun ranging from
46 to 70 million km
Mercury is the smallest planet in the Solar
System:
One of five planets visible with the naked eye a,
Mercury is just 4,879 Kilometres across its equator,
compared with 12,742 Kilometres for the Earth.
Mercury is the second densest planet:
Even though the planet is small, Mercury is very
dense. Each cubic centimetre has a density of 5.4
grams, with only the Earth having a higher density.
This is largely due to Mercury being composed
mainly of heavy metals and rock.
Mercury has wrinkles:
As the iron core of the planet cooled and contracted,
the surface of the planet became wrinkled. Scientist
have named these wrinkles, Lobate Scarps. These
Scarps can be up to a mile high and hundreds of
miles long.
Mercury has a molten core:
In recent years scientists from NASA have come to
believe the solid iron core of Mercury could in fact
be molten. Normally the core of smaller planets
cools rapidly, but after extensive research, the
results were not in line with those expected from a
solid core. Scientists now believe the core to contain
a lighter element such as sulphur, which would lower
the melting temperature of the core material. It is
estimated Mercury’s core makes up 42% of its
volume, while the Earth’s core makes up 17%.
Mercury is only the second hottest planet:
Despite being further from the Sun, Venus
experiences higher temperatures. The surface of
Mercury which faces the Sun sees temperatures of up
to 427°C, whilst on the alternate side this can be as
low as -173°C. This is due to the planet having no
atmosphere to help regulate the temperature.
Mercury is the most cratered planet in the Solar
System:
Unlike many other planets which “self-heal” through
natural geological processes, the surface of Mercury
is covered in craters. These are caused by numerous
encounters with asteroids and comets. Most
Mercurian craters are named after famous writers
and artists. Any crater larger than 250 kilometres in
diameter is referred to as a Basin. The Caloris Basin
is the largest impact crater on Mercury covering
approximately 1,550 km in diameter and was
discovered in 1974 by the Mariner 10 probe.
Only two spacecraft have ever visited Mercury:
Owing to its proximity to the Sun, Mercury is a
difficult planet to visit. During 1974 and 1975
Mariner 10 flew by Mercury three times, during this
time they mapped just under half of the planet’s
surface. On August 3rd 2004, the Messenger probe
was launched from Cape Canaveral Air Force Station,
this was the first spacecraft to visit since the mid
1970’s.
Mercury is named for the Roman messenger to
the gods:
The exact date of Mercury’s discovery is unknown as
it pre-dates its first historical mention, one of the
first mentions being by the Sumerians around in
3,000 BC.
Mercury has an atmosphere (sort of):
Mercury has just 38% the gravity of Earth, this is too
little to hold on to what atmosphere it has which is
blown away by solar winds. However while gases
escape into space they are constantly being
replenished at the same time by the same solar
winds, radioactive decay and dust caused by
micrometeorites

VENUS FACTS
Venus is the second planet from the Sun and is the
second brightest object in the night sky after the
Moon. Named after the Roman goddess of love and
beauty, Venus is the second largest terrestrial planet
and is sometimes referred to as the Earth’s sister
planet due the their similar size and mass. The
surface of the planet is obscured by an opaque layer
of clouds made up of sulfuric acid.
Planet Profile
Mass: 4,867,320,000,000,000 billion kg (0.815 x
Earth)
Equatorial Diameter: 12,104 km
Polar Diameter: 12,104 km
Equatorial Circumference: 38,025 km
Known Moons: none
Notable Moons: none
Orbit Distance: 108,209,475 km (0.73 AU)
Orbit Period: 224.70 Earth days
Surface Temperature: 462 °C
First Record: 17th century BC
Recorded By: Babylonian astronomers
Size Of Venus Compared To The Earth
Facts About Venus
A day on Venus lasts longer than a year:
It takes 243 Earth days to rotate once on its axis. The
planet’s orbit around the Sun takes 225 Earth days,
compared to the Earth’s 365.
Venus is often called the Earth’s sister planet:
The Earth and Venus are very similar in size with only
a 638 km difference in diameter, Venus having
81.5% of the Earth’s mass. Both also have a central
core, a molten mantle and a crust.
Venus rotates counter-clockwise:
Also known as retrograde rotation. A possible reason
might be a collision in the past with an asteroid or
other object that caused the planet to alter its
rotational path. It also differs from most other
planets in our solar system by having no natural
satellites.
Venus is the second brightest object in the night
sky:
Only the Moon is brighter. With a magnitude of
between -3.8 to -4.6 Venus is so bright it can be seen
during daytime on a clear day.
Atmospheric pressure on Venus is 92 times
greater than the Earth’s:
While its size and mass are similar to Earth, the small
asteroids are crushed when entering its atmosphere,
meaning no small craters lie on the surface of the
planet. The pressure felt by a human on the surface
would be equivalent to that experienced deep
beneath the sea on Earth.
Venus is also known as the Morning Star and the
Evening Star:
Early civilisations thought Venus was two different
bodies, called Phosphorus and Hesperus by the
Greeks, and Lucifer and Vesper by the Romans. This
is because when its orbit around the Sun overtakes
Earth’s orbit, it changes from being visible after
sunset to being visible before sunrise. Mayan
astronomers made detailed observations of Venus as
early as 650 AD.
Venus is the hottest planet in our solar system:
The average surface temperature is 462 °C, and
because Venus does not tilt on its axis, there is no
seasonal variation. The dense atmosphere of around
96.5 percent carbon dioxide traps heat and causes a
greenhouse effect.
A detailed study of Venus is currently underway:
In 2006, the Venus Express space shuttle was sent
into orbit around Venus by the European Space
Agency, and is sending back information about the
planet. Originally planned to last five hundred Earth
days, the mission has been extended several times.
More than 1,000 volcanoes or volcanic centres larger
than 20 km have been found on the surface of Venus.
The Russians sent the first mission to Venus:
The Venera 1 space probe was launched in 1961, but
lost contact with base. The USA also lost their first
probe to Venus, Mariner 1, although Mariner 2 was
able to take measurements of the planet in 1962.
The Soviet Union’s Venera 3 was the first man-made
craft to land on Venus in 1966.
At one point it was thought Venus might be a
tropical paradise:
The dense clouds of sulphuric acid surrounding Venus
make it impossible to view its surface from outside
its atmosphere. It was only when radio mapping was
developed in the 1960s that scientists were able to
observe and measure the extreme temperatures and
hostile environment. It is thought Venus did once
have oceans but these evaporated as the planets
temperature increased.

JUPITER FACTS
The planet Jupiter is the fifth planet out from the
Sun, and is two and a half times more massive than
all the other planets in the solar system combined. It
is made primarily of gases and is therefore known as
a “gas giant”.
Jupiter Planet Profile
Mass: 1,898,130,000,000,000,000 billion kg (317.83
x Earth)
Equatorial Diameter: 142,984 km
Polar Diameter: 133,709 km
Equatorial Circumference: 439,264 km
Known Moons: 67
Notable Moons: Io, Europa, Ganymede, & Callisto
more info
Known Rings: 4
Orbit Distance: 778,340,821 km (5.20 AU)
Orbit Period: 4,332.82 Earth days (11.86 Earth years)
Surface Temperature: -108°C
First Record: 7th or 8th century BC
Recorded By: Babylonian astronomers
Size Of Jupiter Compared To The Earth
Facts About Jupiter
Jupiter is the fourth brightest object in the solar
system:
Only the Sun, Moon and Venus are brighter. It is one
of five planets visible to the naked eye from Earth.
The ancient Babylonians were the first to record
their sightings of Jupiter:
This was around the 7th or 8th century BC. Jupiter is
named after the king of the Roman gods. To the
Greeks, it represented Zeus, the god of thunder. The
Mesopotamians saw Jupiter as the god Marduk and
patron of the city of Babylon. Germanic tribes saw
this planet as Donar, or Thor.
Jupiter has the shortest day of all the planets:
It turns on its axis once every 9 hours and 55
minutes. The rapid rotation flattens the planet
slightly, giving it an oblate shape.
Jupiter orbits the Sun once every 11.8 Earth
years:
From our point of view on Earth, it appears to move
slowly in the sky, taking months to move from one
constellation to another.
Jupiter has unique cloud features:
The upper atmosphere of Jupiter is divided into
cloud belts and zones. They are made primarily of
ammonia crystals, sulfur, and mixtures of the two
compounds.
The Great Red Spot is a huge storm on Jupiter:
It has raged for at least 350 years. It is so large that
three Earths could fit inside it.
Jupiter’s interior is made of rock, metal, and
hydrogen compounds:
Below Jupiter’s massive atmosphere (which is made
primarily of hydrogen), there are layers of
compressed hydrogen gas, liquid metallic hydrogen,
and a core of ice, rock, and metals.
Jupiter’s moon Ganymede is the largest moon in
the solar system:
Jupiter’s moons are sometimes called the Jovian
satellites, the largest of these are Ganymeade,
Callisto Io and Europa. Ganymeade measures 5,268
km across, making it larger than the planet Mercury.
Jupiter has a thin ring system:
Its rings are composed mainly of dust particles
ejected from some of Jupiter’s smaller worlds during
impacts from incoming comets and asteroids. The
ring system begins some 92,000 kilometres above
Jupiter’s cloud tops and stretches out to more than
225,000 km from the planet. They are between
2,000 to 12,500 kilometres thick.
Eight spacecraft have visited Jupiter:
Pioneer 10 and 11, Voyager 1 and 2, Galileo, Cassini,
Ulysses, and New Horizons missions. The Juno
mission is its way to Jupiter and will arrive in July
2016. Other future missions may focus on the Jovian
moons Europa, Ganymede, and Callisto, and their
subsurface oceans.

NEPTUNE FACTS
Neptune is the eighth planet from the Sun and is the
most distant planet from the Sun. This gas giant
planet may have formed much closer to the Sun in
early solar system history before migrating to its
present position.
Planet Profile
Mass: 102,410,000,000,000,000 billion kg (17.15x
Earth)
Equatorial Diameter: 49,528 km
Polar Diameter: 48,682 km
Equatorial Circumference: 155,600 km
Known Moons: 14
Notable Moons: Triton more info
Known Rings: 5
Orbit Distance: 4,498,396,441 km (30.10 AU)
Orbit Period: 60,190.03 Earth days (164.79 Earth
years)
Surface Temperature: -201 °C
Discover Date: September 23rd 1846
Discovered By: Urbain Le Verrier & Johann Galle
Facts About Neptune
Neptune was not known to the ancients:
It is not visible to the naked eye and was first
observed in 1846. Its position was determined using
mathematical predictions. It was named after the
Roman god of the sea.
Neptune spins on its axis very rapidly:
Its equatorial clouds take 18 hours to make one
rotation. This is because Neptune is not solid body.
Neptune is the smallest of the ice giants:
Despite being smaller than Uranus, Neptune has a
greater mass. Below its heavy atmosphere, Uranus is
made of layers of hydrogen, helium, and methane
gases. They enclose a layer of water, ammonia and
methane ice. The inner core of the planet is made of
rock.
The atmosphere of Neptune is made of hydrogen
and helium, with some methane:
The methane absorbs red light, which makes the
planet appear a lovely blue. High, thin clouds drift in
the upper atmosphere.
Neptune has a very active climate:
Large storms whirl through its upper atmosphere,
and high-speed winds track around the planet at up
600 meters per second. One of the largest storms
ever seen was recorded in 1989. It was called the
Great Dark Spot. It lasted about five years.
Neptune has a very thin collection of rings:
They are likely made up of ice particles mixed with
dust grains and possibly coated with a carbon-based
substance.
Neptune has 14 moons:
The most interesting moon is Triton, a frozen world
that is spewing nitrogen ice and dust particles out
from below its surface. It was likely captured by the
gravitational pull of Neptune. It is probably the
coldest world in the solar system.
Only one spacecraft has flown by Neptune:
In 1989, the Voyager 2 spacecraft swept past the
planet. It returned the first close-up images of the
Neptune system. The NASA/ESA Hubble Space
Telescope has also studied this planet, as have a
number of ground-based telescopes.

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