Newsletter: 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.
by
Robert Piccioni
August 22, 2011
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* * * * * * * * * * * * * * * *
Dr Robert
Piccioni,
Author of "Everyone's
Guide to Atoms, Einstein, and the Universe"
and " Can Life Be
Merely An Accident?"
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