The galaxy in which we live is called the Milky Way galaxy. The pictures below show what we think it would look like if we could see from the outside.

The above images also show our location within the Milky Way. Where we are in the galaxy determines what we see. Using the equator of the Milky Way (the thin disk that in which we are located) as a reference plane, astronomers have devised a Sun-centered latitude-longitude system called the Galactic Coordinate system. In this system the center of the galaxy is at longitude = 0, latitude = 0. The galactic poles are represented by latitude = 90 and - 90.

From studies like the previous exercise you have just done, we've found that globular clusters are very old, much older than the open clusters. This means that they formed much earlier in the history of the Milky Way. In fact, the globular clusters formed around the time the entire galaxy was forming from the merging of many small clouds of gas and "dark matter". The open clusters formed later (and are still forming) in the disk of the Galaxy. Since the galaxy had a different shape when the globular clusters formed the globular clusters are distributed quite differently in space compared to the open clusters. To investigate this difference you will use the interactive exercise below to plot the positions of open and globular clusters on a grid based on the Galactic Coordinate system.


CLICK HERE for the Interactive Activity


When you are done with the above activity you should notice that the two types of clusters are distributed differently with respect to the galactic plane. The problems page contains some questions about these differences.

13. Describe the major difference in the distributions of the open and globular clusters on Galactic co-ordinate grid. Be specific by explaining what part of the Galaxy the open and globular clusters are associated with. 

14. Relate what you have learned about the ages and distributions of globular clusters and open clusters to the formation of the Milky Way galaxy.

EXTRA CREDIT

15. In which type of cluster would you expect to find a B0 star?    

16. In which type of cluster would you expect to find a white dwarf?