Question

Explain Hubble’s scheme of galaxy classification. Why has this scheme proved
enduring? What class has been assigned to the Milky Way Galaxy?

Answer 1

According to Hubble’s scheme, there are four types of galaxies: elliptical, spiral, barred spiral, and irregular. An elliptical galaxy shows no spiral structure and can vary from almost round to almost cigar shaped. Spiral galaxies have outstretched, curving arms suggestive of a whirlpool or pinwheel. Barred spirals show the same spiral structure as normal spirals, and also a prominent bar through the nucleus. Irregulars galaxies lack either an obvious spiral structure or nuclear bulge, appearing instead as a random collection of stars with no obvious order.

Hubble’s classification is based on our perspective from Earth and not on the actual shape.

Milky Way Galaxy is a fairly typical barred spiral galaxy with four major arms in its disk, at least one spur, and a newly discovered outer arm.