What is a Galaxy?What is a Galaxy?

• A galaxy is A galaxy is made of billions made of billions of stars, dust, of stars, dust, and gas all held and gas all held together by together by gravity. gravity.

• Galaxies are Galaxies are scattered scattered throughout the throughout the Universe. They Universe. They vary greatly in vary greatly in size, color and size, color and shape. Not all shape. Not all galaxies look galaxies look alike.alike.

• 4 Main Types–Regular Spiral

(S)–Barred Spiral

(SB)–Elliptical (E)–Irregular (Irr)

• Spirals outwardSpirals outward

–Like a Pin WheelLike a Pin Wheel

Disk ShapedDisk Shaped

- - Like orbit pathsLike orbit paths

• How are galaxies classified?

–Shape

Development of GalaxiesDevelopment of Galaxies

• Sa Sb Sc: arms loosen as the go away from the nucleus

• SBaSBbSBc arms loosen as the go away from the nucleus

• E0 E3 E7S0: no arms but becomes more elliptical shape

• IRR: No Shape

Age of Galaxies

• Age: • Sa Sb Sc: Arms have younger stars in

them and nucleus has older stars

• SBaSBbSBc: Arms have younger stars in them and nucleus has older

• E0 E3 E7S0: Made up of Mostly Old stars

• IRR:Made up of Mostly young stars

•Born: November 20, l889

•BS University of Chicago

•PhD Astronomy

•Hubble revolutionized our knowledge of the size, structure, and properties of the universe.

REVIEWREVIEW

• There are billions of galaxies in the universe.

• They are different shapes, colors, and sizes.

• Edwin Hubble classified galaxies based on their shape, using the “Tuning Fork Diagram.”

• There are Elliptical, Spiral, Barred Spiral, Irregular, and SO shaped galaxies.

Can you identify any galaxies in this picture?Can you identify any galaxies in this picture?