M9 globular cluster, Hubble Space Telescope (HST) image. Combined optical and infrared image of the Messier 9 (M9) globular star cluster. This image resolves stars right into the centre of the cluster, showing their different colours. Redder colours signify lower surface temperatures, while blue stars are extremely hot. M9 is 25,000 light years from Earth, in the constellation of Ophiuchus. Image data obtained with the HST's Advanced Camera for Surveys (ACS) instrument. Image published in 2012.