Telescopes of Captain James Cook.

Thomas M. wrote:

The reflector in the article is not an SCT. It is a simple Cassegrain,
possibly Classical or Gregorian, as the Gregorians were often resorted to
during the era of the "brass" telescope (the tube length argues for a
Gregorian). The SCT is a different and much more recent design (circa

1962)

using spherical optics and a large corrector plate. Clear skies to you.
--



Some of you have a real bad habit of splitting hairs...the concept or
priciple is the same!


No, I'm afraid that it is not really "splitting hairs" at all. Its a matter
of learning and *correctly* using the standard terminology of Astronomical
equipment which has been established at least for the past 40 years if not
longer. The principle behind the SCT is different than that of the purely
reflecting telescopes like Newtonians and Cassegrain instruments, and it was
not the principle used for the telescope noted in the article.
The first reflector telescope design was the Newtonian (invented in
1668), which uses a parabolidal primary and a smaller flat "diagonal"
secondary mirror to send the light collected by the primary mirror out a hole
in the side of the tube. The special parabolidal shape is necessary to form a
fully-corrected image. The second reflecting telescope design was the
Cassegrain (proposed by Guillaume Cassegrain in the year 1677), which uses a
convex secondary mirror to send the light back through a hole in the main
mirror. Like the Newtonian, the design is *purely* a reflector, as it uses
*only* reflective optics (a paraboloidal primary and a hyperboloidal
secondary). The Gregorian is similar to the Classical Cassegrain, but uses a
concave secondary mirror behind the primary focal point to redirect the light
through a hole in the main mirror. These telescopes are *purely* reflective
or "Catoptric" instruments, since they only use mirrors to form their primary
images (except for the eyepiece). They rely only on reflective optics to
create an on-axis image which is corrected for things like spherical aberration.
The term "SCT" stands for "Schmidt-Cassegrain Telescope" which is a
noticably-different design from the Classical Cassegrain or the Newtonian.
It falls into the class of "Catadioptric" or "mirror-lens" telescopes, which
use *both* refractive optics *and* reflective optics to form their main images
(ie: lenses *and* mirrors). It is a derrivative of the Schmidt Camera, and,
like its predecessor, the SCT uses a full-aperture 'corrector plate' out in
front of the telescope to introduce an opposite form of spherical aberration
to that produced by the spherical primary mirror. The secondary mirror then
lengthens the focal length and directs the light back through a hole in the
primary mirror. The use of spherical optics and the special corrector plate
is an attempt to deal with off-axis aberrations like Coma. Without the
corrector plate, the images could be nearly useless, so the principle is not
the same as that used for pure reflectors like Newtonians and Classical
Cassegrain telescopes. Clear skies to you.
--
David W. Knisely
Prairie Astronomy Club: http://www.prairieastronomyclub.org
Hyde Memorial Observatory: http://www.hydeobservatory.info/

**********************************************
* Attend the 11th Annual NEBRASKA STAR PARTY *
* July 18-23, 2004, Merritt Reservoir *
* http://www.NebraskaStarParty.org *
**********************************************

"Thad Floryan" wrote in message
om...
Larry Brown wrote in message
...
In case you haven't seen the page about Captain James Cook. It took me
over two years to research this and find out what telescopes he actually
took with him. The answer came from a ship's manifest. You can find the
pages he
http://www.antiquetelescopes.org/cook.html
I have also added a page about fake antique telescopes.
I can't help wondering if the name Captain James T Kirk was taken from
Captain James Cook. Cook was a real explorer who went where no man had
gone before, after all.

That's for sure. He was eaten by the native cannibals in Hawaii who refer
to this (apparent) delicacy as "long pig".

Even though this was an obvious attempt at humor, I must take exception to
your basic premise. While it is true that Cook was killed by Hawaiians when
he turned out to be a rather fallible human being, he was not eaten.
Although prevalent on some South Pacific islands (e.g, Fiji, New Guinea),
native Hawaiians did not practice cannibalism.

I think I was told once its Gregorian - note the long tube for the 4' ap at f/6.

Only the Gregorians had such low focal lengths - ???
jerry


David Knisely wrote:

Thomas M wrote:

I thought the SCT principle was much younger than that...its an F6 SCT in
the article

The reflector in the article is not an SCT. It is a simple Cassegrain,
possibly Classical or Gregorian, as the Gregorians were often resorted to
during the era of the "brass" telescope (the tube length argues for a
Gregorian). The SCT is a different and much more recent design (circa 1962)
using spherical optics and a large corrector plate. Clear skies to you.
--
David W. Knisely
Prairie Astronomy Club: http://www.prairieastronomyclub.org
Hyde Memorial Observatory: http://www.hydeobservatory.info/

**********************************************
* Attend the 11th Annual NEBRASKA STAR PARTY *
* July 18-23, 2004, Merritt Reservoir *
* http://www.NebraskaStarParty.org *
**********************************************

you need to learn something about optical systems. You are wildly off!
sorry -

jerry



Thomas M wrote:

"David Knisely" wrote in message
...
Thomas M wrote:

I thought the SCT principle was much younger than that...its an F6 SCT
in
the article

The reflector in the article is not an SCT. It is a simple Cassegrain,
possibly Classical or Gregorian, as the Gregorians were often resorted to
during the era of the "brass" telescope (the tube length argues for a
Gregorian). The SCT is a different and much more recent design (circa
1962)
using spherical optics and a large corrector plate. Clear skies to you.
--


Some of you have a real bad habit of splitting hairs...the concept or
priciple is the same!

Jerry Warner wrote:

I think I was told once its Gregorian - note the long tube for the 4' ap at f/6.

Only the Gregorians had such low focal lengths - ???
jerry

I think that some of them did have somewhat shorter focal lengths. The
Gregorian might have been easier to make, since it used only concave optics
and these were easier to test than convex surfaces. I recall a club program
put on by Dr. Eugene Rudd of UNL (Antique Telescope Society) who brought
several of these wonderful brass instruments to our meeting. One was a 3 or 4
inch Gregorian, and although the instrument looked wonderful, I understand
that the performance wasn't all that hot. Clear skies to you.
--
David W. Knisely
Prairie Astronomy Club: http://www.prairieastronomyclub.org
Hyde Memorial Observatory: http://www.hydeobservatory.info/

**********************************************
* Attend the 11th Annual NEBRASKA STAR PARTY *
* July 18-23, 2004, Merritt Reservoir *
* http://www.NebraskaStarParty.org *
**********************************************

"Larry Brown" wrote in message
...
In case you haven't seen the page about Captain James Cook. It took me
over two years to research this and find out what telescopes he actually
took with him. The answer came from a ship's manifest. You can find the
pages he
http://www.antiquetelescopes.org/cook.html

Nice site. Thanks for that.
Mind if I add a link to it from http://faxmentis.org/html/transit.html ?

Jeff

"Kilolani" wrote in message thlink.net...
"Thad Floryan" wrote in message
om...
Larry Brown wrote in message
...
[...]
I can't help wondering if the name Captain James T Kirk was taken from
Captain James Cook. Cook was a real explorer who went where no man had
gone before, after all.

That's for sure. He was eaten by the native cannibals in Hawaii who refer
to this (apparent) delicacy as "long pig".

Even though this was an obvious attempt at humor, I must take exception to
your basic premise. While it is true that Cook was killed by Hawaiians when
he turned out to be a rather fallible human being, he was not eaten.
Although prevalent on some South Pacific islands (e.g, Fiji, New Guinea),
native Hawaiians did not practice cannibalism.

Be that as it may, many others disagree with you (esp. regarding
Capt Cook; see last entry about 30 lines below), and a simple search
found over 7,150 references to cannibalism in Hawaii, the first two
of which are at:

http://apdl.kcc.hawaii.edu/~oahu/stories/waialua/killing.htm

where we find:

" According to Nakuina's story, the last ali'i to live at O'ahunui
" was named O'ahunui. (No ali'i by this name appears in the genealogies
" of Malo, Kamakau, or Kepelino.) O'ahunui took to eating human flesh
" under the influence of cannibal chiefs called Lo-'Aikanaka, who came
" from the South Seas and settled at Mokule'ia in Waialua. "'Aikanaka"
" means, literally, "people-eater," metaphorically, a strong warrior or
" a ruler of men (A chief named 'Aikanaka appears in the 'Ulu genealogy
" as the father of Hema; he resided in Hana, Maui, and was known as an
" industrious and kind chief, not a cannibal [Beckwith Hawaiian
" Mythology 241-243]; according to one Tahitian tradition, Nona, the
" grandmother of Hema, was a cannibal [Henry Ancient Tahiti 552]).

and at URL:

http://www.sacred-texts.com/pac/hloh/

Select Chapter XIII ("The Cannibal Dog Man") and we find:

" This kupua never attacked or injured any members of the family of the
" very high chief or king of the island Oahu, but he was a cannibal, and
" many of the people were killed and eaten by him.

What astounded me was at URL:

http://en.wikipedia.org/wiki/Cannibal

where we learn that the Ukraine is still the country with the highest
number of living cannibals!

But the clincher regarding Capt. Cook is here at URL:

http://www.captaincooksociety.com/ccsu68.htm

where we find:

" 14/Feb/1779 Death of Captain James Cook at Kealakekua Bay, Hawaii;
" murdered by natives (body dismembered and parts eaten)

I first read about that (Cook and cannibals) circa mid-1950s, so if it's
wrong there's a worldwide conspiracy dissing Hawaii.

Looks to me like they've made a mistake in the article. While the
reflector is probably a cassegrain or gregorian the focal length
doesn't appear to be 24 inches as the tube length would appear to be
in that range. The f number would therefore have to be in the range of
at least 18.


"Kilolani" wrote in message thlink.net...
"Thad Floryan" wrote in message
om...
Larry Brown wrote in message
...
In case you haven't seen the page about Captain James Cook. It took me
over two years to research this and find out what telescopes he actually
took with him. The answer came from a ship's manifest. You can find the
pages he
http://www.antiquetelescopes.org/cook.html
I have also added a page about fake antique telescopes.
I can't help wondering if the name Captain James T Kirk was taken from
Captain James Cook. Cook was a real explorer who went where no man had
gone before, after all.

That's for sure. He was eaten by the native cannibals in Hawaii who refer
to this (apparent) delicacy as "long pig".

Even though this was an obvious attempt at humor, I must take exception to
your basic premise. While it is true that Cook was killed by Hawaiians when
he turned out to be a rather fallible human being, he was not eaten.
Although prevalent on some South Pacific islands (e.g, Fiji, New Guinea),
native Hawaiians did not practice cannibalism.

I stand corrected.

"Thad Floryan" wrote in message
om...

*snip*

But the clincher regarding Capt. Cook is here at URL:

http://www.captaincooksociety.com/ccsu68.htm

where we find:

" 14/Feb/1779 Death of Captain James Cook at Kealakekua Bay, Hawaii;
" murdered by natives (body dismembered and parts eaten)

I first read about that (Cook and cannibals) circa mid-1950s, so if it's
wrong there's a worldwide conspiracy dissing Hawaii.

David Knisely wrote in message ...
Thomas M wrote:

I thought the SCT principle was much younger than that...its an F6 SCT in
the article

The reflector in the article is not an SCT. It is a simple Cassegrain,
possibly Classical or Gregorian, as the Gregorians were often resorted to
during the era of the "brass" telescope (the tube length argues for a
Gregorian). The SCT is a different and much more recent design (circa 1962)
using spherical optics and a large corrector plate. Clear skies to you.
--
David W. Knisely
Prairie Astronomy Club: http://www.prairieastronomyclub.org
Hyde Memorial Observatory: http://www.hydeobservatory.info/

**********************************************
* Attend the 11th Annual NEBRASKA STAR PARTY *
* July 18-23, 2004, Merritt Reservoir *
* http://www.NebraskaStarParty.org *
**********************************************

What little I have read about James Short suggests it was a Gregorian
with a parabolic mirror. The guy was pretty impressive he made
something like 1,360 telescopes during his life.

Clear skys
James King