Scales in Space and Timein the Cosmos

By Dr. Harold Williams

of Montgomery College Planetariumhttp://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.

16 x 16 m16 x 16 m

A Campus Scene

1 mile x 1 mile1 mile x 1 mile

A City View

100 miles x 100 miles100 miles x 100 miles

The Landscape of Pennsylvania

Diameter of the Earth: 12,756 kmDiameter of the Earth: 12,756 km

Earth

Distance Earth – Moon: 384,000 kmDistance Earth – Moon: 384,000 km

Earth and Moon

Distance Sun – Earth = 150,000,000 kmDistance Sun – Earth = 150,000,000 km

Earth orbiting around the Sun

Approx. 100 AUApprox. 100 AU

The Solar System

Approx. 10,000 AUApprox. 10,000 AU

(Almost) Empty Space Around our Solar System

Approx. 17 light yearsApprox. 17 light years

The Solar Neighborhood

The Solar NeighborhoodNew 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:

Proxima Centauri, at a distance of 4.2 light yearsApprox. 17 light yearsApprox. 17 light years

Approx. 1,700 light yearsApprox. 1,700 light years

The Extended Solar Neighborhood

Diameter of the Milky Way: ~ 75,000 lyDiameter of the Milky Way: ~ 75,000 ly

The Milky Way Galaxy

Distance to the nearest large galaxies: several million light Distance to the nearest large galaxies: several million light

yearsyears

The Local Group of Galaxies

Large-Scale Structure

Distribution of bright galaxies in the Virgo region indicates the Virgo cluster and presence of more distant, larger scale structure

Clusters of galaxies are grouped into superclusters.Clusters of galaxies are grouped into superclusters.Superclusters form filaments and walls around voids.Superclusters form filaments and walls around voids.

The Universe on Very Large Scales

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 …

The Accelerating Universe

Red Shift z

Ap

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nt M

ag

nitu

de o

f T

ype

Ia S

upe

rno

vae

Flat decelerating universe

Flat accelerating universe

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.