What is a Galaxy? A galaxy is made of billions of stars, dust, and gas all held together by gravity.A galaxy is made of billions of stars, dust, and gas all held together by gravity. Galaxies are scattered throughout the Universe. They vary greatly in size, color and shape. Not all galaxies look alike.Galaxies are scattered throughout the Universe. They vary greatly in size, color and shape. Not all galaxies look alike.

4 Main Types –Regular Spiral (S) –Barred Spiral (SB) –Elliptical (E) –Irregular (Irr)

Spirals outwardSpirals outward –Like a Pin Wheel

Disk Shaped - Like orbit paths

How are galaxies classified? –Shape

Development of Galaxies Sa  Sb  Sc: arms loosen as the go away from the nucleus SBa  SBb  SBc  arms loosen as the go away from the nucleus E0  E3  E7  S0: 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 SBa  SBb  SBc: Arms have younger stars in them and nucleus has older E0  E3  E7  S0: 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.

REVIEW 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?