Grade 6 – Cluster 4
The History of Space
Our understanding about the
universe changes over time.
New information can causes us
to rethink what we know and
reevaluate how we understand
the universe.
History of Space
Over time, objects categorized as planets have
changed.
The ancient Greeks believed the Earth's moon and sun
were planets along with Mercury, Venus, Mars, Jupiter,
and Saturn. Earth was not considered a planet, but
thought to be the central object around which all the
other celestial objects orbited.
History of Space
By the 17th century,
astronomers realized
that the sun was the
object around which
all the planets orbit,
and that the moon is
not a planet, but a
satellite (moon) of
Earth.
History of Space
Uranus was added as a planet in 1781 and
Neptune was discovered in 1846.
History of Space
Pluto, discovered in 1930, was identified as the ninth
planet.
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History of Space
What Makes a Planet According to the International
Astronomical Union?
Planet
Dwarf
Planet
X
X
X
X
X
X
Is in orbit around the sun.
Has sufficient mass to assume a nearly round shape.
Is not a satellite (moon).
Has cleared the neighbourhood of its orbit.
X
Has not cleared the neighbourhood of its orbit.
X
How did the planets get their names?
• The official names of planets and their moons are
governed by an organization called the International
Astronomical Union (IAU).
• The IAU was established in 1919.
Our Planets - Mercury
Mercury is only slightly
larger than Earth's moon.
Our Planets - Mercury
Like the moon, Mercury has very little atmosphere
to stop impacts and it is covered with craters.
Our Planets - Mercury
Mercury's dayside
is super-heated by
the sun, but at
night
temperatures drop
hundreds of
degrees below
freezing. Ice may
even exist in
craters.
Our Planets - Mercury
Mercury's eggshaped orbit
takes it around
the sun every 88
days.
Our Planets - Venus
Venus is only a little smaller than Earth.
Our Planets - Venus
One day on Venus
lasts as long as
243 Earth days
(the time it takes
for Venus to
rotate or spin
once).
Our Planets - Venus
Venus is a
rocky planet,
also known as
a terrestrial
planet. Venus'
solid surface is
a cratered and
volcanic
landscape.
Our Planets - Venus
Venus makes a
complete orbit
around the sun in 225
Earth days.
Our Planets - Earth
If the sun were as tall as a typical front door, Earth
would be the size of a nickel.
Our Planets - Earth
• One day on Earth takes 24 hours (this is the
time it takes the Earth to rotate or spin once).
• Earth makes a complete orbit around the sun (a
year in Earth time) in about 365 days.
Our Planets - Earth
Earth's atmosphere
protects us from
incoming meteoroids,
most of which break
up in our atmosphere
before they can strike
the surface as
meteorites.
Our Planets - Earth
Earth is the perfect
place for life.
Our Planets - Mars
If Earth were
the size of a
nickel Mars
would be
about as big
as an aspirin
tablet.
Our Planets - Mars
One day on Mars takes just a little over 24 hours
(the time it takes for Mars to rotate or spin once).
Our Planets - Mars
Mars makes a
complete orbit
around the sun
(a year in
Martian time) in
687 Earth days.
Our Planets - Mars
At this time in the planet's
history, Mars' surface
cannot support life. A key
science goal is
determining Mars' past
and future potential for
life.
Our Planets - Jupiter
If Earth would be the
size of a nickel and
Jupiter would be about
as big as a basketball.
Our Planets - Jupiter
One day on Jupiter takes about 10 hours (the time it
takes for Jupiter to rotate or spin once).
Our Planets - Jupiter
Jupiter makes a
complete orbit
around the sun (a
year in Jovian time)
in about 12 Earth
years (4,333 Earth
days).
Our Planets - Jupiter
Jupiter is a gas-giant planet and does not have a
solid surface. However, it is predicted that Jupiter
has an inner, solid core about the size of the Earth.
Our Planets - Jupiter
Jupiter's Great Red
Spot is a gigantic
storm (bigger than
Earth) that has
been raging for
hundreds of years.
Our Planets - Saturn
Saturn is the second largest planet, and
comparable in size to Jupiter.
Our Planets - Saturn
One day on Saturn takes 10.7 hours (the time it takes
for Saturn to rotate or spin once).
Our Planets - Saturn
Saturn makes a
complete orbit around
the sun (a year in
Saturnian time) in 29
Earth years.
Our Planets - Saturn
Saturn cannot support life as we know it. However,
some of Saturn's moons have conditions that might
support life.
Our Planets - Uranus
Earth would be the size of a nickel and Uranus would
be about as big as a baseball.
Our Planets - Uranus
One day on Uranus
takes about 17 hours
(the time it takes for
Uranus to rotate or
spin once).
Our Planets - Uranus
Uranus makes a
complete orbit
around the sun (a
year in Uranian
time) in about 84
Earth years.
Our Planets - Uranus
Like Venus, Uranus has a retrograde rotation (east to
west). Unlike any of the other planets, Uranus rotates
on its side, which means it spins horizontally.
Our Planets - Neptune
If Earth would be the size of a nickel and Neptune would
be about as big as a baseball.
Our Planets - Neptune
One day on Neptune
takes about 16 hours
(the time it takes for
Neptune to rotate or
spin once).
Our Planets - Neptune
Neptune makes a
complete orbit around
the sun (a year in
Neptunian time) in
about 165 Earth years
(60,190 Earth days).
Our Planets - Neptune
At times during the course of Neptune's orbit, dwarf
planet Pluto is actually closer to the sun, and us, than
Neptune. This is due to the unusual elliptical (egg)
shape of Pluto's orbit.
Our Planets - Pluto
Is Pluto a planet?