This image also conceals an astronomical interloper. A minor asteroid, only a handful of kilometers across, can be seen streaking across the upper left-hand side of this image. The trail of the asteroid is visible as four streaks of light separated by small gaps. These streaks of light represent the four separate exposures that were combined to create this image, the small gaps between each observation being necessary to change the filters inside NASA/ESA Hubble’s Advanced Camera for Surveys (ACS). Capturing an asteroid was a fortunate side effect of a larger effort to observe every known galaxy close to the Milky Way. When this project was first proposed, roughly 75% of all the Milky Way’s near galactic neighbors had been imaged by Hubble. A group of astronomers proposed using the gaps between longer Hubble observations to capture images of the remaining 25%. The project was an elegantly efficient way to fill out some gaps not only in Hubble’s observing schedule, but also in our knowledge of nearby galaxies.
