Ten years ago the Hubble Space Telescope revealed that the core of the Andromeda Galaxy is actually a double nucleus.

On the left is a typical ground image of M31, one of our closest galactic neighbors and visible to the naked eye as a spindle-shaped "cloud" the width of the full moon. The well-known "Bulge" at its center is apparent.

Above right shows the detail of this bulge, as known before Hubble; a smooth system of old stars. The individual points of light are some of Andromeda's 600 globular clusters, each containing several hundred thousand stars. The background is dark because the contrast was adjusted to bring out detail in the core, which is much brighter than the bulge.

Below right is Hubble's green-light, high resolution image taken on July 6, 1991. It shows two peaks about 5 ly. apart, each containing a few million densely packed stars. The brighter one to the left is the "classic" or traditional nucleus as studied from the ground; Hubble reveals that the dimmer component on the right is the true "center" of M31.