3.02 Galaxy Classification Lab MOD

Galaxies can also be classified by their shape.

• Elliptical galaxies look smooth and plain. Their shapes can be round or stretched out.

• Spiral galaxies have arms that curve out from a round center. The arms can be tight or loose, and some have a bar shape in the middle.

• Lenticular galaxies have a round center and a flat disk, but no spiral arms.

• Irregular galaxies don’t have a clear shape. They might have been other types but got stretched or pulled by nearby galaxies.

In 1927, Edwin Hubble made a way to group galaxies by their shapes. This system is still used today. It’s called Hubble’s "tuning fork" because it looks like a sideways tuning fork.

• Elliptical galaxies are labeled from E0 (perfectly round) to E7 (very stretched out).

• Lenticular galaxies are called S0. They are between elliptical and spiral galaxies.

• Spiral galaxies have two types: unbarred and barred.

  • Unbarred spirals go from Sa (arms are tight with a bright center) to Sc (arms are loose with a dimmer center).

  • Barred spirals go from SBa (tight arms with a clear bar in the center) to SBc (loose arms with a faint bar).

• Irregular galaxies do not fit into Hubble’s system.

Galaxies can be classified by the color of their stars.

Think about what you know about star lifecycles.

Remember that most stars can be found in the Main Sequence for the majority of their lives.

Young blue and white stars are the hottest and brightest. There are young yellow, orange, and red stars, but they aren't as hot or bright.

Once stars are older and run out of hydrogen to fuse to helium, they become red giants or supergiants. These stars are cooler, but still very bright.

White dwarfs are also older stars that are very hot, but they are very dim and hard to see.