Star Systems & Galaxies Chapter 15 Section 4 Star Systems & Galaxies

Star Systems Most stars are members of a group Binary Star: Two Stars Alpha Centauri A & B What is so cool about this star system? Eclipsing Binary: Star eclipses Remember: What’s an eclipse?

Star Clusters Open Clusters Globular Cluster Loose and disorganized A few thousand stars Globular Cluster Round and densely packed Very old stars Millions of stars

Galaxies Spiral Galaxies 30 percent of all galaxies Disk-shaped Large: 20,000 -125,000 light-years Contain both young and old stars More stars at the center Barred-spiral galaxies: Stars form a bar through the nucleus with arms extending outward

More Galaxies. . . Elliptical Galaxies 60 percent of galaxies Can be round or oval Small: Largest is 200,000 light-years No arms More 3D shape Very little gas and dust

And More Galaxies. . . Irregular Galaxies 10 percent of the known galaxies Irregular shape (Not spiral or elliptical) Usually small 1,000 - 20,000 light years No symmetry Contain young stars Were once spiral or elliptical, but gravity has deformed the shape

Milky Way Galaxy Large Spiral Galaxy 100,000 light-years wide 10,000 light-years thick Three major arms

Milky Way Where is our sun? Sagittarius Arm Orion Spur 2/3 away from nucleus 30,000 light-years Revolves around nucleus Orbit = 200 million years

Quasar “quasi” stars – “like stars” Active young galaxies Giant black hole centers Extremely bright! Very strong gravity

The Size of our Universe How big are we compared to the universe? How big is Earth? The sun? What’s bigger?

The Size of our Universe