Download ScalesOfSpace&Time

Scales in Space and Time
in the Cosmos
By Dr. Harold Williams
of Montgomery College Planetarium
http://montgomerycollege.edu/Departments/planet/
The Scale of the Cosmos
• Astronomy deals with objects on a vast range of
size scales and time scales.
• Most of these size and time scales are way
beyond our every-day experience.
• Humans, the Earth, and even the solar
system are tiny and insignificant on cosmic
scales.
A Campus Scene
16 x 16 m
A City View
1 mile x 1 mile
The Landscape of
Pennsylvania
100 miles x 100 miles
Earth
Diameter of the Earth: 12,756 km
Earth and Moon
Distance Earth – Moon: 384,000 km
Earth orbiting around the Sun
Distance Sun – Earth = 150,000,000 km
The Solar System
Approx. 100 AU
(Almost) Empty Space
Around our Solar System
Approx. 10,000 AU
The Solar Neighborhood
Approx. 17 light years
The Solar Neighborhood
New distance scale:
1 light year (ly) =
Distance traveled by light in 1 year
= 63,000 AU = 1013 km
= 10,000,000,000,000 km
(= 1 + 13 zeros)
= 10 trillion km
Nearest star to the Sun:
Approx. 17 light years
Proxima Centauri, at a distance of
4.2 light years
The Extended Solar
Neighborhood
Approx. 1,700 light years
The Milky Way Galaxy
Diameter of the Milky Way: ~ 75,000 ly
The Local Group of Galaxies
Distance to the nearest large galaxies: several million light years
Large-Scale Structure
Distribution of bright galaxies in the Virgo region indicates the
Virgo cluster and presence of more distant, larger scale structure
The Universe on Very Large Scales
Clusters of galaxies are grouped into superclusters.
Superclusters form filaments and walls around voids.
Large-Scale Structure
A large survey of distant galaxies shows
the largest structures in the universe:
Filaments and walls of galaxy
superclusters, and
voids, basically empty space.
Cosmology with the Cosmic
Microwave Background
If the universe was perfectly homogeneous on all scales
at the time of reionization (z = 1000), then the CMB
should be perfectly isotropic over the sky.
Instead, it shows small-scale fluctuations:
Measuring the “Deceleration”
of the Universe …
By observing type Ia
supernovae,
astronomers can
measure the Hubble
relation at large
distances
Distance 
recession speed
Size scale of the
universe  rate
of expansion
It was expected that this would measure the
deceleration of the universe, but …
Apparent Magnitude of
Type Ia Supernovae
The Accelerating Universe
Flat decelerating universe
Flat accelerating universe
Red Shift z
In fact, SN Ia measurements showed that the
universe is accelerating!
The Evolution and Ultimate
Fate of the Universe
Until ~ 6 billion
years ago,
gravity of matter
was stronger
than acceleration
Today,
acceleration
due to dark
energy
dominates.