Question A3 The figure below shows the Hertzsprung-Russell diagram (HRD) for two star clusters using data from the Gaia mission (Gaia Data Release 2, A&A 2018). The absolute magnitude and colour index are defined using a Gaia defined photometric system. MG -2 0- 2 4- 16 Open Cluster M 67 8- Globular Cluster 47 Tuc 0.0 0.5 1.0 1.5 2.0 2.5 GBP - GRP a) Briefly describe the morphological (i.e., shape related) properties of open and globular clusters. b) Explain the form of the HRD for the two clusters, indicating on a sketch the main features. c) Explain how the age of a star cluster can be determined, making clear the assumptions required. d) From the figure what can you infer about the ages of the two clusters shown? Explain your reasoning.

Question A3 The figure below shows the Hertzsprung-Russell diagram (HRD) for two star clusters using data from the Gaia mission (Gaia Data Release 2, A&A 2018). The absolute magnitude and colour index are defined using a Gaia defined photometric system. MG -2 0- 2 4- 16 Open Cluster M 67 8- Globular Cluster 47 Tuc 0.0 0.5 1.0 1.5 2.0 2.5 GBP - GRP a) Briefly describe the morphological (i.e., shape related) properties of open and globular clusters. b) Explain the form of the HRD for the two clusters, indicating on a sketch the main features. c) Explain how the age of a star cluster can be determined, making clear the assumptions required. d) From the figure what can you infer about the ages of the two clusters shown? Explain your reasoning.