Our Universe StructureSmallest to largest:

PlanetsStars/Solar systemsGalaxiesGalaxy ClustersUniverse

Universe contains hundreds of billions of galaxies.

Galaxies contain hundreds of billions of stars.Imagine the possibility of finding life.

Life on other planets IS possible!If only one planet in each galaxy had life. . .

Now imagine the probability of finding it!1.0 X 1022!

Distance - factorsDistance indicators = objects

whose diameter or absolute magnitude is KNOWN

Look-back time = looking at galaxies millions of light-years away = looking at light that left galaxy millions of years ago, like looking back in time.

DistancesAstronomical Unit = distance between

Earth and Sun, 93 million mi. (solar system)

Recall: Light Year = distance light travels in one year, 9.46 X1015 m (near by stars)

Parsec = 3.08 X 1016 m = 3.26 light years (stars within our galaxy)

Megaparsec = 1 Mpc = 3.26 million light years (galaxy clusters & galaxies)

Types of Galaxies

SpiralEllipticalIrregular

Spiral Galaxies

Usually disk shaped with a greater concentration of stars in the center.

Arms sweep outward.20% of all galaxies - From nucleus10% of all galaxies - From a rigid bar

Tend to spin faster in the center.Contain both young and old stars

Has both gas and dust to make new stars!

Milky Way Galaxy

Spiral galaxy example100,000 L.Y. across10,000 L.Y. thick at the nucleusThree spiral arms (splintered)Our solar system is 2/3 way down one

arm (30,000 L.Y. away from nucleus)Spherical halo/bubble made of gas and

globular clusters.

Milky Way Edge View

Artist Milky Way Galaxy

Artist Milky Way Galaxy

Elliptical GalaxiesRange of shapes- round to oval

Depends on our frame of reference!Depends on eccentricity.

Most are small, but the largest galaxies known are elliptical200,000 L.Y. diameter

60% of all galaxiesNo arms or barsNo visible gas or dust-which means no

NEW stars are forming.Composed of old starsLack hot, bright starsStars concentrated near center.

Elliptical Galaxy NGC 4881

Irregular Galaxies

Make up 10% of known galaxiesComposed of young and old stars

Clouds of gas and dust w/o nucleus or arms Huge! Can see 2 with your eye alone

Large and Small Magellanic CloudsNamed after Magellan who discovered them

in 1520.150,000 L.Y. away, nearest neighbors

Large Magellanic Cloud

Small Magellanic Cloud

eaRTH SPACe scienceAll galaxy types represented.

Make your own at: http://mygalaxies.co.uk

Galaxy Clusters

Group of stars is a galaxyGalaxies are also grouped into clustersMay contain thousands of galaxiesOur cluster is called the Local Group

Has at least 28 galaxiesGalaxy clusters can be grouped into

superclustersBelieved to be the largest grouping in the

universe.

CollisionsMay dominate galaxy evolutionGalaxies collide, stars don’t

Galaxies are much closer together than stars

Causes rapid star formation and one may “steal” gas/dust from the other.Galactic cannibalismMilky way vs. Large & Small Magellanic

cloudsEvidence in distortions and computer

modelsLast a hundred million years

Galactic Cannabilism

Image of Lg. Magellenic cloud. Dots are stars stolen from Sm. Mag. Cloud. Proof = opposite rotation, odd orbits, and different composition of LMC. (rotation, orbit, & composition similar to SMC)

Cartwheel Galaxy

Hubble’s Law Edwin Hubble, 1929 Realized that dimmer galaxies are likely

farther away. The farther the galaxy, the greater the red

shift. Red shift = when a light source is moving away

from the observer, the light waves get “stretched” causing it to appear redder than it really is.

Hubble’s law - the farther the galaxy is from us, the faster it is moving away.

Vr=Hd, H = Hubble’s constant, value still being determined (70-100 km/sec/Mpc)

Red Shift

Top = Red shift: object moving away

Middle = No shift: object not moving toward or away

Bottom = Blue shift: object moving toward

Example: Sounds/Doppler Effect