AAO image reference AAT 70. « Previous || Next »
Top left is NE. Image width is about 4.6 arc min
Image and text © 1991-2010, Australian Astronomical Observatory, photograph by David Malin.
Many astronomers have invested much time and effort in measuring the subtle colours of stars in these ancient stellar gatherings and their colour-magnitude diagrams, which compare brightness and colour, show a considerable range of hues. The colours indicate the temperature at the stellar surface and range from yellow for the coolest to blue for the hottest. In this picture, made from a series of three, 2-minute AAT exposures, the colours of the brighter stars are clearly seen, especially the large number of blue, 'horizontal branch' stars. These stars affect the overall colour of the cluster significantly, making its integrated light slightly bluer than that of the Sun. M5 is in the constellation of Serpens at a distance of about 25,000 light-years.
For details of photographic exposure, search technical table by AAT reference number.