Unit 1: The Big PictureUnit 1: The Big Picture

What is Astronomy? What is Astronomy?

The study of stars & anything outside The study of stars & anything outside EarthEarth– Not Not astrologyastrology…no horoscope reading here!…no horoscope reading here!

Today we will go overToday we will go over– Universe Creation (how did it all begin?)Universe Creation (how did it all begin?)– Universe CompositionUniverse Composition– Universe Size (how big is it??)Universe Size (how big is it??)

Universe CreationUniverse CreationBig Bang Theory – universe literally explodes into Big Bang Theory – universe literally explodes into existence.existence.– Temperature: universe cooled from about 10Temperature: universe cooled from about 102323K K

to about 10to about 101010K within the first secondK within the first second– Temp dropped below 1 billion K after only 3 Temp dropped below 1 billion K after only 3

minutes, to 3000K after a million years, to 300K minutes, to 3000K after a million years, to 300K todaytoday

*Water freezes at 273K and boils at 373K*Water freezes at 273K and boils at 373K– 10102323= 1,000,000,000,000,000,000,000,000= 1,000,000,000,000,000,000,000,000

A few artists’ renditions of the Big Bang

SizeSizeIncreased in size by 10Increased in size by 103030 in less than 10 in less than 10-30-30 sec. sec. (started out the size of an atom and grew (started out the size of an atom and grew instantlyinstantly to the size of a galaxy) to the size of a galaxy)Continues to grow as galaxies are moving away Continues to grow as galaxies are moving away from each other…Hubble’s Lawfrom each other…Hubble’s Law

Estimated age is 10-16 billion yearsEstimated age is 10-16 billion yearsSo, it’s REALLY BIG, SUPER BIG, BEYOND So, it’s REALLY BIG, SUPER BIG, BEYOND COMPREHENSIONCOMPREHENSION

CompositionComposition

4 sec-temp too low for converting energy 4 sec-temp too low for converting energy into matter, too high to form atomsinto matter, too high to form atoms

3 minutes – nuclei can form 3 minutes – nuclei can form – 25% helium nuclei, 75% hydrogen nuclei w/ small 25% helium nuclei, 75% hydrogen nuclei w/ small

amounts of lithium and boron nucleiamounts of lithium and boron nuclei

300,000 years before temps cool enough 300,000 years before temps cool enough to form atomsto form atoms– 25% Helium, 75% hydrogen mix25% Helium, 75% hydrogen mix

Composition Composition Solar System: group of planets, moons, debris Solar System: group of planets, moons, debris moving around a starmoving around a star

Interstellar Space: space between stars filled with Interstellar Space: space between stars filled with dust, gas, etc. dust, gas, etc.

Galaxy: systems of billions of starsGalaxy: systems of billions of stars– 200 billion stars in the Milky Way200 billion stars in the Milky Way– Billions of galaxies in universe each with Billions of galaxies in universe each with

potentially hundreds of solar systemspotentially hundreds of solar systems

Are we alone??Are we alone??

Composition ContinuedComposition ContinuedIntergalactic Space: the space between galaxies. Intergalactic Space: the space between galaxies. mostly nothing, can’t see it, gravitational pull mostly nothing, can’t see it, gravitational pull toward it existstoward it exists

Galaxy Clusters: small group of galaxies Galaxy Clusters: small group of galaxies – Closest is Sagittarius galaxy 75,000 LY, Magellanic Closest is Sagittarius galaxy 75,000 LY, Magellanic

Clouds, then AndromedaClouds, then Andromeda

Superclusters: groups of galaxy clustersSuperclusters: groups of galaxy clusters

Cosmic Voids: space between superclustersCosmic Voids: space between superclusters

Milky Way Galaxy

Galaxy Cluster

Important DistancesImportant Distances*Astronomical Unit (AU) = distance from sun to earth *Astronomical Unit (AU) = distance from sun to earth

(93 million miles)(93 million miles)

*62.25 AU = 1 light year = 6 trillion miles *62.25 AU = 1 light year = 6 trillion miles

*Light year = distance light travels in 1 year *Light year = distance light travels in 1 year

Is the light we see from stars and other objects in

the sky

“up to date”?

Important distances to put in all in perspectiveImportant distances to put in all in perspective

Earth’s diameter: 8,000 milesEarth’s diameter: 8,000 milesSolar System diameter: about 8 billion milesSolar System diameter: about 8 billion milesDistance to nearest star: 4.3 LY (Alpha Centauri)Distance to nearest star: 4.3 LY (Alpha Centauri)

Distance across the Milky Way: 100,000 LYDistance across the Milky Way: 100,000 LYDistance to Andromeda Galaxy: 2.5 million LYDistance to Andromeda Galaxy: 2.5 million LYDistance across local group: 4 million LYDistance across local group: 4 million LYDistance across our supercluster: 100 million LYDistance across our supercluster: 100 million LY

**Bottom Line: There are billions of galaxies in **Bottom Line: There are billions of galaxies in the universe each containing billions of the universe each containing billions of

stars!stars!

Day 2: GalaxiesDay 2: GalaxiesGalaxy: systems of billions of stars, “island Galaxy: systems of billions of stars, “island universes”universes”– Thought Milky Way made up entire universe until Thought Milky Way made up entire universe until

1920s1920s– Small fuzzy patches in telescopes appeared as Small fuzzy patches in telescopes appeared as

nebulae, Latin for cloudsnebulae, Latin for clouds– Edwin Hubble measured approximate distance to Edwin Hubble measured approximate distance to

nearby Andromeda…no way Milky Way was that nearby Andromeda…no way Milky Way was that largelarge

– 3 Types: spiral, elliptical, irregular3 Types: spiral, elliptical, irregular

Spiral Galaxies (Milky Way)Spiral Galaxies (Milky Way)

Nucleus, halo, disk, Nucleus, halo, disk, spiral armsspiral arms

Gas & dust visibleGas & dust visible

Spin in direction Spin in direction indicated by armsindicated by arms

Barred spiral: bar of Barred spiral: bar of stars running through stars running through nucleus…page 505 in nucleus…page 505 in textbook for diagramstextbook for diagrams

Elliptical GalaxiesElliptical Galaxies

Sphere or squashed Sphere or squashed sphere shape with sphere shape with nucleus and halonucleus and haloNo spiral arms, little dust No spiral arms, little dust or gasor gasMade almost entirely of Made almost entirely of old reddish starsold reddish starsStars orbit, but not all in Stars orbit, but not all in the same path…don’t the same path…don’t rotaterotateRange in size from giant Range in size from giant to dwarfto dwarfDwarf is the most Dwarf is the most common type of galaxycommon type of galaxy

Irregular GalaxiesIrregular Galaxies

Lacking regular shapesLacking regular shapes

Large and Small Large and Small Magellanic Clouds are Magellanic Clouds are among nearest neighbors among nearest neighbors which are which are – visible in the Southern visible in the Southern

HemisphereHemisphere– Look like clouds detached Look like clouds detached

from Milky Wayfrom Milky Way– Believed to be pulling apart Believed to be pulling apart

due to gravitational pull due to gravitational pull from Milky Wayfrom Milky Way

Our Home: The Milky WayOur Home: The Milky WayMade up of 200 billion stars, dust and gasMade up of 200 billion stars, dust and gas

Gases absorb light from stars and give a Gases absorb light from stars and give a band of light in the skyband of light in the sky– Difficult to see stars in other spiral armsDifficult to see stars in other spiral arms– Scientists use radio & infrared waves to Scientists use radio & infrared waves to

penetrate dustpenetrate dust

Spiral arms due to trailing of larger stars Spiral arms due to trailing of larger stars more distant than smaller stars more distant than smaller stars

Black hole center Black hole center

Sun located on inner edge of Orion armSun located on inner edge of Orion arm

Two types of stars: Two types of stars:

– Population I: bright blue Population I: bright blue stars in the spiral arms, stars in the spiral arms, younger stars ( 10 BY younger stars ( 10 BY and younger, Sun)and younger, Sun)

– Population II: located in Population II: located in the halo, bulge, and the halo, bulge, and globular clusters, older globular clusters, older stars (13 BY and older)stars (13 BY and older)

Milky Way FactsMilky Way Facts

Diameter of diskDiameter of disk 100,000 LY100,000 LY

Thickness of diskThickness of disk 2,000 LY 2,000 LY

Distance of Sun from Center 25,000 LYDistance of Sun from Center 25,000 LY

Number of StarsNumber of Stars 200 Billion200 Billion

Time for Sun Time for Sun 200 Million years 200 Million years

to make 1 circuitto make 1 circuit