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E1 – Introduction to the Universe
Let’s make a model!
The Solar System
Let’s answer some
questions! (“Planet
patterns”)
Main points
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Know the names of the planets!
They orbit in ellipses with the sun at one foci
Inner planets small and rocky
Outer planets large and mainly gas
Outer planets are much further from the sun
Asteroid belt between Mars and Jupiter
Comets
Comets
• Giant dirty snow balls (ice and dust) (diameter
100m - 50 km?)
• Very elliptical orbits
• Short period (T < 200 yrs) and long period
(could be thousands of years)
• Oort cloud
• Tail(s) always point away from the sun
• Evaporate as they get closer to the sun
My address
11507 Meadow Lake Drive
Houston
Texas 77077
USA
My address
11507 Meadow Lake Drive
Houston
Texas 77077
USA
Earth
My address
11507 Meadow Lake Drive
Houston
Texas 77077
USA
Earth
Solar System
My address
11507 Meadow Lake Drive
Houston
Texas 77077
USA
Earth
Solar System
Milky way
My address
11507 Meadow Lake Drive
Houston
Texas 77077
USA
Earth
Solar System
Milky way
Local group
My address
11507 Meadow Lake Drive
Houston
Texas 77077
USA
Earth
Solar System
Milky way
Local group
Universe
Galaxy
Galaxies
• A large collection of stars, gas and dust held
together by their mutual gravity.
• Dwarf galaxies might have only a few million
stars, many galaxies have hundreds of billions.
• The Universe has around 100 billion galaxies
Astronomical unit (1 AU)
An astronomical unit (AU) is the average
distance of the earth from the sun which is
150 million km
1 AU = 1.5 x 1011 metres
Light Year
Defined as the distance
travelled by light in one year
1 ly = 3 x 108 x 365 x 24 x 60 x 60 = 9.46 x 1015 m
Distance between stars in a galaxy
About one parsec (defined later)
One parsec is 3.26 light years
Distance between galaxies
• 100 kpc for galaxies in clusters
• A few Mpc for galaxies in different clusters
Constellations
• The pattern of the stars
remains the same from
night to night (over the
time of a life-time)
• These patterns have
been labelled
constellations
Orion’s
belt
Constellations
• The constellations do not
appear in the same place
• Over the period of one
night they appear to
rotate around the pole
star
• Some stars rise above
the horizon during the
night, and some set
behind it.
Constellations
• This same movement is continued during the day. The
sun rises in the east and sets in the west. Maximum
height at midday (in the south in the Northern
hemisphere.
Constellations
• The constellations visible also depends on the
time of year
Constellation position
• The location of stars also varies slightly at
different times of year due to the change in
position of the earth.
Place to place
• The constellation you can see also depends on
where you are
I’m on top of the world!
I can’t see the pole star!
Constellations – line of sight effect
• The stars in a constellation only appear to be
close
Stellar clusters
• A group of stars that are physically near each
other in space, formed from the same gas
cloud.
Let’s read!
Pages 487 to 492.