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Telescope Night at Mount Wilson Observatory

By John Kounis - Posted on 16 June 2013

60-inch Dome, Mount Wilson I have always had a passion for astronomy. In fact, it was that interest that resulted in my admission to USC, my job at Jet Propulsion Laboratory, and ultimately my membership in the Aero Association of CalTech where I trained for my pilot license. So when Rhonda, a friend of mine with the Valencia Hiking Crew Meetup Group mentioned the opportunity to spend a night observing through the 60-inch telescope at Mount Wilson, I couldn't resist.

Astronomer Harlow Shapley used this telescope to determine the structure of the Milky Way and our location at the edge of the galaxy—rather than in the middle as had been previously thought. His work, along with that of such famous astronomers as George Hale and Edwin Hubble at Mount Wilson ultimately led to the discovery that the Milky Way is just one of many galaxies, dramatically expanding our understanding of just how vast the universe is. Hubble also used the 100-inch telescope at Mount Wilson to discover that the universe is expanding, meaning that the universe had to have a beginning (and possibly an end).

Despite its power, this 1908 telescope can now no longer be used for science in a field dominated by adaptive optics, interferometers, and imaging fiber arrays. The 60-inch telescope is now the largest telescope in the world that is available for public use. Groups of up to 25 can book it for $900 for a half night (until 1 a.m.) or $1,700 for a full night. We paid $37.50 each for a half night. If you want to book it yourself, visit

A Tale of Two Peaks

San Gabriel Peak Trail Since the Valencia Hiking Crew is, after all, a hiking group, we started the day with a five-mile hike to the summits of 5,960-foot Mount Disappointment and 6,161-foot San Gabriel Peak. The route to Mount Disappointment was short, steep, and forested. However, the trail to San Gabriel Peak was thick with poodle dog bush, a poisonous plant that germinates in forest fires. These plants have proliferated throughout the Angeles Forest after the 2009 Station Wildfire.

I managed to complete the hike with only a brief brush against one flower. A fellow hiker, Alice, gave me tecnu skin cleanser to wash up with after the hike. Apparently, this product helps decontaminate skin of the toxic oils after encounters with poison oak and ivy. I hope it is just as effective against poodle dog bush; I will find out for sure in a few days. All the beauty of the tall stalks and purple flowers certainly belies these bushes' danger.

Poodle Dog Bushes


You can check out our hiking route by visiting:

A 24,000-mm Telephoto Lens

Deep-sky Observing Shelley Bonis, our session director, teaches astronomy for UCLA extension, yet is nothing like your typical college professor. According to, she "made the transition from go-go dancer/flower child/social activist to professional astronomer." She was also married to comedian Richard Pryor for three years in the late 1960s. Her gregarious and informative commentary livened up the evening.

The telescope can be used both as a Newtonian reflector at F4.5 and as a Cassegrain reflector at F16. Use as a Newtonian reflector would place the eyepiece at near the top of the telescope, requiring ascending cranes and climbing scaffolds to look through it, which is impractical for a group of 25 people. Therefore, the telescope is configured as a Cassegrain reflector, which places the eyepiece near the bottom, well within reach of a small ladder in almost all configurations.

The 60-inch telescope at Mount Wilson slews quickly and smoothly. To support its weight, it is suspended in a 900-lb. vat of mercury, concealed in the cylinder at the base of the telescope. These days, the mercury is enclosed, but it was open to the air until the 1960s or 1970s. I wonder how many astronomers suffered cognitive issues after inhaling mercury vapors night after night?

When Carla, the telescope operator, said she would take requests for celestial objects, I was excited to suggest galaxies and nebulae that had always appeared faint in my 10-inch, F6 telescope at home. A 60-inch telescope has 36 times the light-gathering capacity. It had to be brighter, right? Wrong. The only factor affecting brightness of an object is the focal ratio, not the focal length. Since the 60-inch telescope was at F16, objects would appear fainter than they would through my F6 telescope at home, albeit 16 times larger, due to the Mount Wilson telescope's 960-inch focal length versus my 60-inch focal length. (That's the equivalent of a 24,400-millimeter telephoto!) Carla and Shelley explained that some objects are just not suited to the 60-inch telescope, either because they are too dim, or because they are too large and you can't see the entire object in the eyepiece due to the tremendously long focal length (e.g. the Andromeda Galaxy).

My wish list included M51, the Whirlpool Galaxy; M57, the Ring Nebula; and M13, the Hercules Cluster. Carla told me that the Whirlpool Galaxy would be too dim and diffuse, but she complied with the other requests.

The moon through the 60-inch telescope

Our evening began at dusk, with an up-close view of the Lunar Terminator. That's not an Arnold Schwarzenegger-like moon man; rather, it's the line between light and dark on the lunar surface where the sun is setting. The low angle of the sun accentuates craters and ridges with long shadows, adding depth to the view. We saw fascinating structures like a long chasm, apparently caused by a glancing blow with a meteorite, as well as craters within craters within craters.

I was able to take the photograph to the right by placing my iPhone up to the 4-inch-diameter, 80mm eyepiece. Unfortunately, it only worked for the moon. (Since the sun is shining on the moon just like it does on Earth, the exposure for a close-up moon photograph is usually pretty close to a daylight setting). Other objects were much too dim for to photograph.

Saturn was equally impressive. We could clearly see the rings, bands in the clouds on the surface, and its moon, Titan. This held a particular interest for me, since the last project I worked on at JPL before starting Pilot Getaways magazine was the Cassini spacecraft, which launched in 1997 and started orbiting Saturn in 2004.

Other objects that rounded out the night were the globular cluster M92 in Hercules, the Cat's Eye Nebula in Draco, and the double star T Draconis.


San Gabriel Peak from Mt. Disappointment Trail
Alice, Rhonda, George, and Leo.
Mount Disappointment Yucca Tree
Mount Disappointment Collage
Poodle Dog Bushes
San Gabriel Peak Trail
San Gabriel Peak
San Gabriel Peak Benchmark
60-inch Dome, Mount Wilson
First-quarter moon
Valencia Hiking Crew in Front of the 60-inch Dome
60-inch telescope
60-inch dome control panel
Evening Coordinator
Observing at dusk
The moon through the 60-inch telescope
Observing Saturn
Deep-sky Observing
Control Console for 60-inch Telescope
Telescope Chair Lift