- Demonstrate an understanding that stars in a constellation are not physically related but that stars in a cluster are associated gravitationally

There are clusters of stars around the galaxy. These have sometimes been mistaken for galaxies but we know they are not as there are usually only several thousand stars quite close to our galaxy, if not in it.

If they actually were galaxies there would be millions of stars there and they would be much further away. In fact we can see clusters of stars in other galaxies.

There are two types you should know about: 
- Open clusters
- Globular clusters


Open clusters are groups of stars close to each other in space. They form no specific symmetry and are usually very bright, indicating that they are young stars.

These can be anywhere from a dozen to thousands of stars making up no particular shape and are found around the galactic plane.

A good example of an open cluster is the Pleiades, or seven sisters, above the constellation Taurus. You can compare your eyesight to a friend by seeing how many you can spot with your eyes. From a city you may see seven, the record is nineteen!


Globular clusters are spherical shaped with more stars nearer the nucleus. They resemble a fuzzy ball.

These clusters are located around the galactic nucleus.

The stars are usually very old red giants and white dwarfs packed tightly together. There are thought to be between 100,000 to over a million stars in a typical globular cluster.

An example of a globular cluster is M13 in Hercules.


  Open Globular
Star Types Young Stars Old red giants / white dwarfs
Located Galactic Plane Galactic Nucleus
Visual Little Symmetry Spherical
Example Pleiades M13 in Hercules
  • What kind of stars can be found in an open and globular cluster?
  • What is the difference in appearance between an open and globular cluster?