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

Mercury Venus Mars Jupiter Saturn 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

Jovian Terrestrial

Mars 210 ft Earth 138 ft Inner solar-system

Jupiter 719 ft Saturn 1320 ft

Uranus 2651 ft Neptune 4153 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 (9.461×10 12 km) 1 ly ≈ 63,241 AU Interstellar Scales

4.242 ly ly ~ 3.5˚ Sun  Centauri A  Centauri B Proxima Centauri ~0.2 ly (10, ,000 AU) ~ 25 AU

Model for Sol-  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 400 billion stars!!

CD Model for the Milky Way 4.75 in

CD Model for the Milky Way Interstellar distances … 4 ly ≈ 5×10 -5 in ~ cm ~ 1  m ~ 1/10 red blood cell An AU ~ 1  m/63,241 ~ m ~ 1/10 H atom

Intergalactic distances

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 B NASA's Swift satellite (29 April 2009) ~ billion ly Newest: EGSY8p billion ly

Q: How big’s the universe?

A: ∞

10 4