I am a science teacher in 9th grade physical science. One frequently asked question I get is what class of spiral galaxy is the Milky Way? Is it an Sa, Sb, or Sc?
Although it is well accepted that the Milky Way is a spiral galaxy, there is still some contention over what class of spiral it is. Since we are stuck in the middle of it and it is often difficult to get accurate distance to astronomical objects, getting a good 3-D picture has been difficult. If we could only get a view from outside.....!
Anyway this means that the answer to your question is not known. We're not even sure if the Milky Way has a bar or not. I hope that that will satisfy the 9th graders!
Karen was a graduate student at Cornell from 2000-2005. She went on to work as a researcher in galaxy redshift surveys at Harvard University, and is now on the Faculty at the University of Portsmouth back in her home country of the UK. Her research lately has focused on using the morphology of galaxies to give clues to their formation and evolution. She is the Project Scientist for the Galaxy Zoo project.