The video provides an overview of galaxies, which are massive collections of gas, dust, and stars held together by gravity. It explains the Hubble classification system, which categorizes galaxies into four main types: elliptical, spiral, lenticular, and irregular. Elliptical galaxies are featureless and spherical, while spiral galaxies have arms that spiral outward. Lenticular galaxies have a central bulge and a disk-like structure, and irregular galaxies do not fit into the other categories. The video further details the classification of elliptical and spiral galaxies, including subtypes based on shape and arm tightness. It concludes with a mention of additional resources for further learning.

What holds a galaxy together?

• Gravity

• Magnetism

• Electricity

• Nuclear force

How many main types of galaxies are there according to the Hubble classification?

• Four

• Two

• Five

• Three

Which type of galaxy is featureless and spherical in shape?

• Spiral

• Elliptical

• Lenticular

• Irregular

What is a characteristic feature of a barred spiral galaxy?

• No defined shape

• Tightly wrapped arms

• A bar shape in the center

• A central bulge

What is the shape of an E0 elliptical galaxy?

• Highly elongated

• Perfectly spherical

• Irregular

• Disk-like

Which galaxy type is our Milky Way an example of?

• Irregular

• Barred spiral

• Regular spiral

• Elliptical

Which classification is used for regular spiral galaxies?

• S

• E

• I

• SB

What distinguishes an SBc galaxy from an SBa galaxy?

• SBc has a central bulge

• SBc has tightly woven arms

• SBc has loosely wrapped arms

• SBc is featureless

Which type of galaxy is not subdivided further?

• Elliptical

• Spiral

• Irregular

• Lenticular

What letter is used to classify lenticular galaxies?

• S

• SO

• E

• SB