Describe the structure of our galaxy, including its spiral arms.

Unlike a regular spiral, a barred spiral contains a bar across its center region, and has two major arms. The Milky Way also contains two significant minor arms, as well as two smaller spurs. One of the spurs, known as the Orion Arm, contains the sun and the solar system.

Most spiral galaxies consist of a flat, rotating disk containing stars, gas and dust, and a central concentration of stars known as the bulge ... The spiral arms are sites of ongoing star formation and are brighter than the surrounding disc because of the young, hot OB stars that inhabit them.