Hipparcos pinpointed more than 100,000 stars to high precision. Some of these stars have been organised in a diagram called HR (Hertzsprung-Russell). This is a two-dimensional plot of the luminosity of a star versus its colour. Each region of the HR diagram represents certain properties of the star, including its evolutionary stage.
For more information on the Hipparcos mission, please click on the following link: ESA Hipparcos