Labelled wide-field view of the Andromeda Galaxy
This ground-based image of the Andromeda Galaxy shows the location of four fields where the NASA/ESA Hubble Space Telescope has been used to study a wide variety of stars in the Andromeda Galaxy, ranging from faint main sequence stars like our own Sun, to the much brighter RR Lyrae stars, which are a type of variable star. With these measurements, astronomers can determine the chemistry and ages of the stars in each part of the Andromeda Galaxy.
The field marked A is located on the edge of the Andromeda Galaxy's disc.
The field marked B is in the giant stellar stream, a long swathe of stars left over from a smaller galaxy that was engulfed by the Andromeda Galaxy.
Fields C and D are in the halo, a sparse sphere of stars and dark matter that surrounds the galaxy's disc.
Hubble's very long exposures, combined with its excellent image quality, means that it is able to distinguish individual stars in these fields, even though they look virtually empty in this ground-based telescope's image.