Our Universe in Space

(intro survey)

Our solar system’s scale

Convenient distance unit for the solar system: the AU

The astronomical unit (AU) is the average Earth-Sun distance.

1 AU ≈ 150 million kilometers or 93 million miles

MercuryVenusMarsJupiterSaturn

Visible, known to ancients

Uranus – William Herschel 1781

Neptune – predicted Urbain Le Verrier observed Johann Galle 1846

Pluto – predicted Percival Lowell observed Clyde Tombaugh 1930

– demoted to ‘dwarf planet’ 2006

JovianTerrestrial

jupiter

earth

Sol

D

D

D

74.9

109

km 1092.13 5

Mars210 ft

Earth138 ft

Inner solar-system

Jupiter719 ft

Saturn1320 ft

Uranus2651 ft

Neptune4153 ft

‘Pluto’5453 ft

How far to nearest star?

Convenient distance unit for interstellar scales: the ly

The Light-Year (ly) is the distance light travels in one year.

1 ly ≈ 9 trillion kilometers or about 6 trillion miles(9.461×1012 km)

1 ly ≈ 63,241 AU

Interstellar Scales

4.242 ly

4.365 ly~ 3.5˚

Sun

a Centauri A

a Centauri B

Proxima Centauri

~0.2 ly(10,000-20,000 AU)

~ 25 AU

Model for Sol- a Centauri separation

Now let’s pretend that Sol was the size of our ball-bearing …

then 4 ly would be 80.3 mi !!

then out to Pluto would be 66 feet

Our Galaxy

The Milky Way

100 to 400billion stars!!

CD Model for the Milky Way

4.75 in

CD Model for the Milky Way

Interstellar distances …4 ly ≈ 5×10-5 in ~ 10-4 cm ~ 1 mm

~ 1/10 red blood cell

An AU ~ 1 mm/63,241 ~ 10-11 m

~ 1/10 H atom

Intergalactic distances

The Local Group

The Local Group

100,000 ly

220,000 ly

The Local Group

100,000 ly

2,500,000 ly

220,000 ly Note: our book says “about 100,000”

4.75 in(100 kly)

10.5 in(220 kly)

119 in or 9 ft 11 in

(2.5 Mly)

(Hercules cluster)

Other clusters of galaxies

Other clusters of galaxies ‘near’ us

Diameter 800 Mly

(Hubble deep-field - Fornax)

Lots of Galaxies !!!

APOD: The galaxies pictured above are part of a cluster of galaxies called ACO 3627 near the center of the Great Attractor. Previously, this cluster of galaxies, also known as the Norma Cluster, was largely unstudied because dust in the disk of our own Galaxy obscured much of its light. The Great Attractor is a diffuse mass concentration fully 250 million light-years away, but so large it pulls our own Milky Way Galaxy and millions of others galaxies towards it. Many of the galaxies in ACO 3627 are slowly heading towards collisions with each other.

The Great Attractor

Large-scale structure of the universe?

Sloan 2 degree galactic redshift survey ….

62,559 galaxies!

( 1 pc ~ 3.3 ly )

(3.3 billion ly )

Observable size of (our) universe

Q: Why is the night sky dark??

• Finite universe?• Finite age of universe?• Other

A: The universe hasn’t lasted forever.

Age of the universe ~ 14 billion years (13.82 billion years latest estimate)

We can’t see anything older than 14 billion light years

gamma-ray burst known as GRB 090429B NASA's Swift satellite  (29 April 2009)

~13.095 billion ly

Newest: EGSY8p7 13.2 billion ly

Q: How big’s the universe?

A: ∞

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