The blaze has reached over 41,000 acres and is only 3% contained as of Wednesday morning.
Hundreds of firefighters have been battling the blaze since it started Sept. 6 near the Cogswell Dam and West Fork Day Use area.
The observatory posted to Facebook on Tuesday that the blaze was less than one-third of a mile down the mountain as a timelapse showed the approaching flames.
Angeles National Forest officials said that firefighters were able to protect the historic site.
"Assisted by the outstanding defensible space of Mt. Wilson Observatory, firefighters installed hand and dozer line - strategically fired, and dropped water creating a strong protection point for Mt. Wilson," officials tweeted.
The observatory is where astronomers confirmed that galaxies exist outside the Milky Way and that the universe is expanding.
The blaze remains a threat to foothill communities but officials say the fire behavior has moderated. The cause of the blaze remained under investigation, according to FOX11.
Since Sunday U.S. Forest Service officials pushed back the estimated time for full containment from Oct.15 to Oct. 30.
Evacuation orders remain for parts of Sierra Madre and Arcadia due to the blaze.
The South Coast Air Quality Management District has also extended a smoke advisory through Wednesday for most areas of Los Angeles County, even the coasts, due to the smoke from the blaze.
California is experiencing its worst fire season on record, with more than 3 million acres burned so far. The Bobcat Fire is one of several fires that sparked across the region as parts of California saw record-breaking temperatures over Labor Day weekend
More than 16,000 firefighters are battling blazes across the state.
The Associated Press contributed to this report.