Section 3: The UniverseSection 3: The Universe

““Gaining a better understanding of the Gaining a better understanding of the universe gives us more insight into the universe gives us more insight into the possible origin of everything around us”possible origin of everything around us”

GalaxiesGalaxies

Galaxy: huge collection of stars, Galaxy: huge collection of stars, planets, gas, and dust held planets, gas, and dust held together by gravitytogether by gravity

Milky Way is a galaxy that Milky Way is a galaxy that includes our solar systemincludes our solar systemAppears as a milky, hazy white Appears as a milky, hazy white

band but it is actually a huge band but it is actually a huge number of starsnumber of stars

Galaxies form because of gravityGalaxies form because of gravity

The Milky WayThe Milky Way

All Shapes and Sizes…All Shapes and Sizes…

Shapes of GalaxiesShapes of Galaxies Spiral Galaxy: looks Spiral Galaxy: looks

like a pinwheel when like a pinwheel when viewed from aboveviewed from above Long “arms” spiraling Long “arms” spiraling

out from centre coreout from centre core Viewed from the side, Viewed from the side,

looks like a dinner looks like a dinner plate with a bulge in plate with a bulge in the centrethe centre

Ex. Milky WayEx. Milky Way

Shapes of GalaxiesShapes of Galaxies

Elliptical galaxy: Range in shape from Elliptical galaxy: Range in shape from perfect sphere to stretched out perfect sphere to stretched out ellipseellipseContain some of the oldest stars in the Contain some of the oldest stars in the

universeuniverseMakes up >50% of universeMakes up >50% of universeLargest known galaxies are ellipticalLargest known galaxies are ellipticalEx. Centaurus AEx. Centaurus A

Centaurus ACentaurus A

Shapes of GalaxiesShapes of Galaxies Irregular galaxy: Do not have a regular, Irregular galaxy: Do not have a regular,

recognizable shape such as a spiral or a recognizable shape such as a spiral or a central bulgecentral bulge Lack of shapeLack of shape ““The Bird”The Bird”

Star ClustersStar Clusters

““Open Cluster”Open Cluster” 50 -100 stars50 -100 stars Appear along the main Appear along the main

band of Milky Way band of Milky Way

““Globular Cluster”Globular Cluster” ≥≥100 000 stars100 000 stars Arranged in distinctive Arranged in distinctive

spherical shapespherical shape Appear around center Appear around center

of Milky Wayof Milky Way

Collection of Stars held together by gravityCollection of Stars held together by gravity

Open ClusterOpen Cluster

Globular ClusterGlobular Cluster

More Milky Way…More Milky Way…Scientists have mapped our galaxy Scientists have mapped our galaxy

using radio waves.using radio waves.Gigantic system of stars, seen as a Gigantic system of stars, seen as a

white band across southern horizonwhite band across southern horizonDiameter: 100 000 light yearsDiameter: 100 000 light yearsRecall: 1 light year – distance light travels Recall: 1 light year – distance light travels

in 1 yearin 1 year9.5 x 109.5 x 101212 km km

Centre of Milky Way is a sphere of Centre of Milky Way is a sphere of globular clustersglobular clusters

More Milky Way…More Milky Way…

William Herschel counted stars to William Herschel counted stars to figure the apprx. shape of M.W.figure the apprx. shape of M.W.Flat disc with sun in centreFlat disc with sun in centre

Harlow Shapley used star clusters to Harlow Shapley used star clusters to figure out that the sun (and thus our figure out that the sun (and thus our solar system) is nowhere near the solar system) is nowhere near the centrecentre

The Sun is apprx. 28 000 light years away from The Sun is apprx. 28 000 light years away from the centre of the Milky Way (the bright bulge)the centre of the Milky Way (the bright bulge)

The Shape of the Milky WayThe Shape of the Milky Way

2 major spiral arms, 2 major spiral arms, numerous minor armsnumerous minor arms

Est. mass: Est. mass:

200 000 000 000 solar 200 000 000 000 solar massesmasses

The Local GroupThe Local Group

Milky Way belongs to a group of ~ 40 Milky Way belongs to a group of ~ 40 galaxies known as the Local Groupgalaxies known as the Local Group

Diameter of the Local Group is ~ 10 Diameter of the Local Group is ~ 10 million light yearsmillion light years

The Milky Way and Andromeda The Milky Way and Andromeda galaxies are the biggest within the galaxies are the biggest within the Local GroupLocal Group

The Local GroupThe Local Group

The Local GroupThe Local Group

The Local GroupThe Local Group

The Local GroupThe Local Group

The Local Group is a The Local Group is a cluster cluster of of galaxiesgalaxies

4 – 25 clusters = a 4 – 25 clusters = a supercluster!supercluster!A gigantic cluster of galaxies, hundreds A gigantic cluster of galaxies, hundreds

of millions of light years in sizeof millions of light years in size

Class WorkClass Work

Think-pair-share!Think-pair-share! In pairs, answer questions 1-4, 7-8In pairs, answer questions 1-4, 7-8

Finish for HWFinish for HW