Astronomical Units

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Astronomical Units Light Years

• Project

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Distance in Space
An ellipse is an oval-shaped path.
An astronomical unit (AU) is the average distance
between Earth and the sun it is about 150
million kilometers.
Light-year The distance that light travels in one
year, about 9.5 trillion kilometers or 63,240 AU
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The speed of light is the fastest speed that
could EVER be achieved. The speed of light is
300,000 km per SECOND!! (Thats 186,000 miles per
second) Light takes 2 seconds to reach the
Earth from the moon - it takes it 8 minutes to
reach the Earth from the Sun
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If you were in a spaceship that travelled at the
speed of light and you started a journey from the
Sun it would take about 3 minutes to reach
Mercury, 5 minutes to reach Venus, 8 minutes to
reach the Earth, 51/2 hours to reach Pluto, 4
years to reach the next star, 5000 years to
reach the edge of the galaxy, 50,000 years to
reach the next galaxy, 500,000 years to reach
the next Cluster!!
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Real rockets dont travel at the speed of light,
they travel MUCH slower. The Apollo missions
took 4 days to reach the moon - at the speed of
light it would have taken 2 seconds!! These
rockets were travelling roughly 200,000 times
slower than light. At this speed it would take
125 YEARS to get to Pluto!
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The Astronomical Unit, au
Earth
The Earths orbit around the sun is not circular
it is elliptical
Sun
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The Astronomical Unit, au
Earth
The average radius of the orbit is defined as
one astronomical unit, au
Sun
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The Astronomical Unit, au
Earth
1 au 1.49 x 1011m
about 150 million kilometers
Sun
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A model of our Solar System

• You will make a scale model with proportional
  astronomical units with respect to the sun
• Make Earth 5 mm in diameter and the rest of the
  planets to scale with respect to the Earth
• Use the internet and/or you Prentice Hall book to
  determine the colors and appearance of each planet

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Table 1 Planet Distances
Planets Distance from the edge of the Sun in AU
Mercury .39
Venus .72
Earth 1.0
Mars 1.5
Asteroid Belt 2.5-2.8
Jupiter 5.2
Saturn 9.2
Uranus 19.2
Neptune 30.0
Pluto 39.4
1 AU 10 cm
3.9 cm
0.39 AU 3.9 cm
Measure from the outer edge of the sun to the
leading edge of the planet
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Table  2 Planet Diameters
Planets Diameter (mm)
Mercury 2.0
Venus 4.75
Earth 5.0
Mars 2.65
Jupiter 56.0
Saturn 47.0
Uranus 20.0
Neptune 19.0
Pluto 1.0
0.2 cm
2.0 mm 0.2 cm
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10 millimeters
?
1 centimeter
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7.2 centimeters
3.9 centimeters
Venus
Mercury