SCALES: PLANETARY
Problem for Astronomers: there is no
sense of depth from looking at the sky.
Comet Hale-Bopp:
10 light-minutes away
Andromeda Galaxy:
2 million light-years away
Proximity on the sky
does not tell us about
proximity in space.
If two stars appear equally bright,
one could be luminous and far
and the other feeble and near.
Apparent size does
not tell us about
proximity in space.
If two monks appear equal size, one could be
adult and far and the other young and near.
Sun and Moon have equal angles in the sky.
Work in groups to set your expectations of
the size of the Solar System and nearby stars.
If the Earth is the size of small lime how far
away and how big are: Moon, Sun, Jupiter,
edge of the Solar System, and nearby stars?
A SCALE MODEL
Star
A large, glowing ball of gas that generates heat
and light through nuclear fusion.
Planet
Mars
Neptune
A moderately large object which orbits a star; it shines
only by reflected light. Planets may be rocky, icy, and
small, or large and gaseous in composition.
Moon
An object that orbits a
planet. Also can be
called a satellite. The
largest moons are as
large as the smallest
planets.
Ganymede (orbits Jupiter)
Asteroid
A relatively small and
rocky object that
orbits a star.
Gaspra
Comet
A relatively small
and icy object
that orbits a star
on an elliptical
orbit.
Hyukatake
Earth shrunk from 13,000km to 4cm
That’s a factor
of 300,000,000
or 300 million
Astronomers measure length in
meters, astronomical units, and
parsecs.
Distance from Earth to Sun
= 150 billion meters
= 1.5 X 1011 meters
= 1 astronomical unit (AU)
Terrestrial Planets = 10,000 km Diam.
Giant Planets = 10x Terrestrial Planets
Solar-type Stars = 10x Giant Planets
Sun is >99% of all Solar System mass
>99% in star
<1% in sum
of planets,
asteroids,
meteors &
comets
Properties of the Sun (a star)
Earth ↑
Diameter = 1.4 million kilometers =
100 × Earth diameter
Mass = 2 × 1030 kilograms =
330,000 × Earth mass
Age = 4.6 billion years
SPACE SCALE MODEL:
Just like a map of the
Earth, this model of a
solar system shrinks it
to a manageable size,
a 1:300,000,000 scale.
•
•
•
•
•
The Moon is a grape at 1m distance
The Sun is a 4m sphere 450 m away
Jupiter is a 0.5m ball 2.5km from Sun
Neptune is a 15cm ball 15 km away
The nearest star is 150,000 km away
TIME SCALE MODEL:
And at this scale, light
is reduced to very fast
walking speed. There’s
no way information in
the universe can travel
any faster than this.
•
•
•
•
The Moon is a seconds walk away
The Sun is 8 minutes walk away
5 hours to walk the Solar System
Years to walk to the nearest stars
The Solar System is Empty
Science isThere
Seeing is the
Sun and
not much else in the
entire volume of the
Solar System. In the
scale model, that is
30 m3 in a volume of
space 3 trillion m3 so
only one part in 100
billion has anything.