The Douglas McLean Memorial Observatory was part of Project 169, established on the planet Hanka by SG-7 under the command of John Smith. The observatory was built to collect data on the accretion disk of a black hole during a local solar eclipse, however Nirrti used a biological agent to wipe out SG-7 and the entire population of the planet in order to hide her experiments in genetic manipulation. O'Neill and Teal'c did remain to observe the eclipse and collect data, however they were also targeted by Nirrti's ships, and the planet was abandoned.
*Cameo - Observatory named for Doug McLean: Art Director
Cross Reference: Hanka
Episode Reference: Singularity