The difference between globular clusters and open clusters is significant and fairly obvious. These two types of star clusters harbor different types of stars. Also, the strength of gravitational bonds between the stars differs significantly.
Open clusters
Open clusters are also known as galactic clusters by some people. This difference in the name is mostly caused by the fact that open clusters are found on the arms of spiral galaxies. On the other hand, the name ‘open cluster’ originates from the fact that stars forming that particular cluster can be distinguished as individual stars without any problems. The distances between them are higher than those between stars in globular clusters.
Open clusters usually contain from a few dozen stars up to a few hundred, although some extremes are known. There are some open clusters that harbor several thousand stars. Stars within the open cluster always have the same origin. They originated from the same nebula, and as a result they travel together. However, the gravitational bonds between these stars are relatively weak. This means that open clusters often get shattered by heavier objects that pass through them. A good example of such an object is a massive star.
The age of the stars is also approximately the same. The stars belonging to open clusters are typically considered to be young stars. The fact that open clusters usually dissolve over time is probably the main reason behind this.
Globular clusters
These groups of tightly bound stars are different than open clusters in many ways. One of the most obvious differences is their size and shape. The number of stars in globular clusters varies from several thousand stars up to one million stars. Also, they are formed in a spherical system.
Gravitational bonds between stars in globular clusters are much stronger than those between stars in open clusters. This causes the spherical shape of globular clusters and the fact that they do not dissolve over the course of time. Actually, stars found in globular clusters are much older than those found in open clusters.
Another difference is that stars within globular clusters are very close to one another. It is often hard to distinguish the individual stars even with the use of telescopes. Star density in open clusters is much lower.
The location of globular clusters within a galaxy usually differs from the location of open clusters. Most known globular clusters are found in halos that surround the galactic plane of spiral galaxies.
To conclude, the difference between globular clusters and open clusters is vast. Differences in shape and size are most obvious. However, the typical location of globular clusters within the galaxy usually differs from that of open clusters, too. The same is true for the age of the stars composing the clusters and the strength of gravitational bonds between the individual stars.
Sources
http://outreach.atnf.csiro.au/education/senior/astrophysics/stellarevolution_clusters.html
http://burro.astr.cwru.edu/stu/advanced/stars_clusters.html
http://answers.yahoo.com/question/index?qid=20090126231239AAm67o0
