Mount Palomar Observatory - part 2

In a prior newsletter, I related the wonderful personal experience Joan and I had spending a night at the Palomar Observatory. Now, I want to explore the science that astronomers do there and what it takes to make a giant telescope work.


After giving a presentation to Friends of Palomar Observatory, we enjoyed a marvelous dinner at the “Monastery” with astronomer Stan Metchev. Stan graduated from Harvard, got his Ph.D. from Caltech, and is now an Assistant Professor at SUNY at Stony Brook.


Stan’s research goal is studying the atmospheres of exoplanets—planets beyond our Solar System—in pursuit of one of humanities’ holiest of holy grails: alien life. As a preparatory step, Stan is refining his technique by studying the atmospheres of brown dwarfs, watching “storms” move across their face as they rotate. He invited us to watch him work that night.


Brown dwarfs are “failed stars” that aren’t massive enough to sustain hydrogen fusion, the power source of true stars. Brown dwarfs span the gap between the heaviest planets at 1% of our Sun’s mass and the lightest stars at 8%. Studying brown dwarfs presents a state-of-the-art challenge, as they can be 10,000 times dimmer than true stars. The best shot is using infrared light and Palomar’s “Big Eye.”


We settled in amidst the Ph.D.’s, astronomy professors, and Jean, the Telescope Operator, who is ultimately in command. Jean’s primary job is to protect the telescope. Astronomers tell Jean what they want to do, and Jean decides if and when to do it. She first evaluates the weather conditions, using an array of instruments and then by touring the dome’s exterior catwalk and surveying the sky. Rain, hale, snow, dust, and fire debris are all hazardous to the telescope’s precision optics. Only if all is clear and the sun has set, does Jean open the dome. While astronomers control the imaging systems, Jean controls the telescope, dome, and its shutters.


While sitting in a heated control room, in front of a myriad of computer displays, Stan explained that doing astronomy has become much more civilized now that imaging is done remotely and electronically. When imaging required film, astronomers had to spend all night in the “cage”, where they changed imaging plates at the top of the telescope, 80 feet above the floor, exposed to the elements. As former Caltech professor and long-time Palomar astronomer, Jesse Greenstein once said, astronomers needed a “tough bladder” to stay in the cage for 10 to 15 hours (winters have longer nights). Any motion within the telescope during an exposure would compromise the image. This picture shows Jesse at age 85, entering the cage for the last time, sitting in the astronomer’s chair.


After focusing the telescope, by moving the cage up and down in steps of 1/10th of an inch, Stan started taking data. One image showed several brown dwarfs and two fuzzy blobs—“they’re probably galaxies” he said. Knowing that Palomar has cataloged millions of galaxies, I naively asked if he could put the cursor on the image and find out which galaxies these were. Stan replied: “No – because no one has ever looked at these stars and galaxies before.” I was shocked. But doing the math confirmed what Stan said. Our universe contains at least 100 billion galaxies, so we’ve cataloged less than 1/100th of 1% of what’s out there. Almost everything out there has never been seen by any human being—there’s virgin sky everywhere.


For nearly 50 years, Palomar’s Hale Telescope was the world’s largest—at 5080mm and f/3.3, it’s truly the “Big Eye.” Astronomers at Palomar have found:

  • 29,000 asteroids,
  • 200 supernovae,
  • one billion stars,
  • millions of galaxies,
  • 20,000 galaxies clusters, and
  • thousands of quasars.


Palomar produced the “Big Picture” now displayed at Griffith Observatory that is 152 feet long and 20 feet high. Palomar also discovered many large bodies orbiting our Sun far beyond Pluto, including Quaoar, Orcus, Sedna, and Eris. As these are comparable, or even larger than Pluto, their discovery forced astronomers to formally define what is a “planet”, ultimately leading to Pluto’s demotion to the status of “dwarf planet.”


The Hale telescope was built between 1934 and 1948, funded by a $6 million gift from the Rockefeller Foundation. The primary mirror is the largest single-piece mirror in any working telescope and many feel it could never be replicated. As cast by Corning Glass, the Pyrex honeycomb mirror weighed 20 tons. Caltech scientists ground the mirror to shape and polished it to optical smoothness, removing about 10,000 pounds of glass. The mirror is cleaned weekly, and re-coated with aluminum about once a year. This image shows the mirror before (top) and after re-coating.




To coat the mirror, it must first be unbolted from the telescope and loaded onto a cart. The cart is then rolled on rails to an open work area. Workers then clean the mirror and strip away the old aluminum coating with acid, as shown at left, where the honeycomb support structure is visible. Imagine how careful they must be not to damage the glass—millionths of an inch really do matter.










Next an 18-ton vacuum chamber cover is lowered onto the cart, which doubles as the vacuum chamber bottom. The chamber is sealed far beyond “air-tight”, and slowly evacuated.  Aluminum is then evaporated inside, coating everything inside with an aluminum film 3-millionth of an inch thick.



It’s all amazing to me.






Best Regards,






 You're never too old or too
  young to ask "Why?"



Dr. Robert Piccioni
Author of "Everyone's Guide to Atoms, Einstein, and the Universe"
and "Can Life Be Merely An Accident?"