100-inch telescope mirror interior bubbles

I've moved a popular page from an obscure corner of my personal web site
to a permanent home that's more appropriate. It's a page about the
bubbles inside the 9000-pound plate glass mirror of the Mount Wilson
Observatory Hooker 100-inch telescope. I had a chance to get some good
photos of the infamous bubbles a couple years ago and made a page to
share the rare view with others. Now that the observatory has a new web
site I've added this page to the online tour. Start at
http://www.mtwilson.edu and click on "Tour Mount Wilson Online". Choose
"100-Inch Hooker Telescope" at the bottom of the list and click on the
first link in the text, "giant mirror". Or if you just want to bring up
that page, go to
http://www.mtwilson.edu/vir/100/mirror/100in_mirror.htm.

Visitors are always fascinated by the view of these bubbles inside the
huge plate glass ("green wine bottle glass") mirror, seeing them from
the back of the mirror through the back of the telescope. I always
point out that ATM's would never accept a blank that looked like this
(and neither did Hale and Ritchey until forced to give it a try). But
these are the first publicly released images that show the actual
structure of the waves of glass, AFAIK. I hope you enjoy seeing them.
For more on the story behind building the 100-inch scope and the bubbles
fiasco, see the article in the History section.

Mike Simmons

On 09/30/03 17:27 +0900, Mike Simmons wrote:

http://www.mtwilson.edu/vir/100/mirror/100in_mirror.htm.

Those are marvelous photos, Mike.

trane
--
//------------------------------------------------------------
// Trane Francks Tokyo, Japan
// Practice random kindness and senseless acts of beauty.
// http://mp3.com/trane_francks/

Trane Francks wrote:

On 09/30/03 17:27 +0900, Mike Simmons wrote:

http://www.mtwilson.edu/vir/100/mirror/100in_mirror.htm.


Those are marvelous photos, Mike.

trane

Indeed ... I am adding the link to my class lecture notes (AST4723C
Techniques of Optical Astronomy II)

Mike Simmons wrote:

I've moved a popular page from an obscure corner of my personal web site
to a permanent home that's more appropriate. It's a page about the
bubbles inside the 9000-pound plate glass mirror of the Mount Wilson
Observatory Hooker 100-inch telescope. I had a chance to get some good
photos of the infamous bubbles a couple years ago and made a page to
share the rare view with others. Now that the observatory has a new web
site I've added this page to the online tour. Start at
http://www.mtwilson.edu and click on "Tour Mount Wilson Online". Choose
"100-Inch Hooker Telescope" at the bottom of the list and click on the
first link in the text, "giant mirror". Or if you just want to bring up
that page, go to
http://www.mtwilson.edu/vir/100/mirror/100in_mirror.htm.

Visitors are always fascinated by the view of these bubbles inside the
huge plate glass ("green wine bottle glass") mirror, seeing them from
the back of the mirror through the back of the telescope. I always
point out that ATM's would never accept a blank that looked like this
(and neither did Hale and Ritchey until forced to give it a try). But
these are the first publicly released images that show the actual
structure of the waves of glass, AFAIK. I hope you enjoy seeing them.
For more on the story behind building the 100-inch scope and the bubbles
fiasco, see the article in the History section.

Mike Simmons

I was puzzled by "The curve of the mirror is 114 inches deep and
required 35 gallons of solution" ... that's a pretty fast f-ratio.

John Oliver wrote:

I was puzzled by "The curve of the mirror is 114 inches deep and
required 35 gallons of solution" ... that's a pretty fast f-ratio.

Yikes! It was supposed to read "1-1/4 inches". I've fixed it (using
the symbol for 1/4 so the same can't happen again). Thanks for pointing
this out, John.

For those wondering what the heck we're talking about, the offending
typo is in the article on construction of the 100-inch scope, not on the
new page I posted about the mirror.

Mike Simmons

John Steinberg wrote:
Mike Simmons wrote:

Visitors are always fascinated by the view of these bubbles inside the
huge plate glass ("green wine bottle glass") mirror, seeing them from
the back of the mirror through the back of the telescope. I always
point out that ATM's would never accept a blank that looked like this
(and neither did Hale and Ritchey until forced to give it a try). But
these are the first publicly released images that show the actual
structure of the waves of glass, AFAIK. I hope you enjoy seeing them.
For more on the story behind building the 100-inch scope and the bubbles
fiasco, see the article in the History section.

Fascinating photos, Mike. Thanks for the pointer and fascinating
history.

Three comments:

- Although the blank is enormous, I can't help but note that the scale
of the observatory itself seems extraordinarily enormous by comparison.
This, of course, a purely subjective impression from a layman.

- Ze French and zere bubbly!

Zey might ouel have used (not so) empty champagne bottles, so the bubbles.

Sorry about that. We'll make sure they are really empty next time.

-- fm
http://dulle.free.fr/alidade/galerie.php?maxim=12

Mike,

that's a greener hue than I thought.
has anyone used interferometry to measure the accuracy of the surface?
Is there any plans of replacing the mirror with better substrate?

NS

John Steinberg wrote:

- Although the blank is enormous, I can't help but note that the scale
of the observatory itself seems extraordinarily enormous by comparison.
This, of course, a purely subjective impression from a layman.

I'm not sure I understand about the "scale of the observatory", John.
Do you mean the dome housing the telescope (rather than the whole
observatory)? It is a huge dome -- 100 feet in diameter and weighing
500 tons (1,000,000 pounds!) -- but it just fits the 100-inch f/5
telescope. Later telescopes were made with shorter focal ratios, partly
to keep the size of the dome from growing too large.

- I'm guessing you've been further massaging the site as the pages that
originally rendered as white in the OS X native Safari browser [1.0 v
85.5)] now appear in the intended gray.

I fixed an error in the cascading style sheets thanks to a tip from a
well-known s.a.a. member. Massaging is scheduled to continue for quite
some time.

Mike Simmons

Francois Meyer wrote:

John Steinberg wrote:

- Ze French and zere bubbly!

Zey might ouel have used (not so) empty champagne bottles, so the bubbles.

Sorry about that. We'll make sure they are really empty next time.

Ah, to have been there for the Grand Emptying of the wine bottles needed
for the mirror blank! :-)

Mike Simmons

Neal Shepard wrote:

Mike,

that's a greener hue than I thought.

It's quite obvious and actually quite beautiful. Visitors that get a
peek at the back of the mirror inside the telescope are generally
impressed by its hue. Users of the 60-inch telescope can also see the
back of that mirror (which has the same color) but not as well.

has anyone used interferometry to measure the accuracy of the surface?

I don't know the method used to test it but one astronomer working on
the new laser guide star adaptive optics system has told me the
three-mirror system is 1/4 wave overall (average 1/12 wave for each
mirror?). I'm often asked about this so I will get more details
(hopefully more useful than that tired old measure) and add them to the
site. Observations when raw seeing is sufficient (which happens on
occasion) indicates diffraction-limited performance, and it has gotten
very good reviews for the past 85 years.

Is there any plans of replacing the mirror with better substrate?

Goodness no! :-) It is a nuisance when temperatures are changing too
rapidly for the glass to follow but that doesn't happen that often and
wouldn't warrant the expense. Along with a new mirror cell for a
thinner mirror of more modern material, a weight would be needed behind
the mirror to make up the remainder of the original's 4.5 tons of
weight. And it would be a crime from a historical aspect, IMHO, unless
it really impacted the science done with it. But it would make quite a
museum exhibit!

Mike Simmons