Galileo's Original Telescopes: New
measurements of their dimensions with special
Galileo's Telescopes: To Date These Are The Worlds
Finest Museum Quality Replicas
Made to Order by Jim & Rhoda Morris
We have built a number of these very fine replicas for the the IMSS in Florence Italy, Griffith Observatory, the Adler Planetarium, and President L. B. Johnson's Library and Museum in Austin, TX. A number, in various configurations, of our replica's IMSS inv #2427 and 2428 were on the exhibit at Beijing Planetarium and are now at the Franklin institute in Philadelphia. We were able to successfully make them to high standard of accuracy after spending a significant amount of research of the literature and making measurements of these instruments using some interesting techniques that we developed for this task
An issue in
dimensions and the solution;
These errors were too large to be ignored in building and using our replicas. It was clear that the lengths and diameters of the various components had to be checked out with new measurements. So with the help of Dr. Giorgio Strano - Curator and the staff at the IMSS we made measurement of the instrument on a number of visits to the IMSS for both the IMSS 2427 and 2428 telescopes. Our measurements did show clearly that both telescopes were considerably shorter than reported. The methods that we employed are discussed below along with the the current dimensions of both telescopes
In addition to our work and impart as a result of our work; . IMSS on (12/4/2008) made new and more accurate measurements of the length of both telescopes The new lengths for IMSS inventory 2427 is (1273 mm not 1360mm) and IMSS inventory 2428 is (927mm. not 980mm). This is very good news for all of us especially those that build models of these famous telescope. We all appreciate the very careful and good work done by the staff at the IMSS.
These new data are reported on their very
wonderful and lively
web sites. Again thank you IMSS for your good work it is so very helpful. to all
of us. and a wonderful example of scientist working together to achieve the best
data. for our and others projects to replicate these instruments.
On our trips to the IMSS we took up the challenge to make our measurements of the original instruments through the display case windows in the exhibit hall before normal exhibit hours.
The windows of the display case are of adequate optical quality to make useful optical measurements. For
these measurements we designed and built our own special portable optical rulers which are
described below. We compiled two sets of data, one in 2005, using a single telescope on a substantial
tripod, the second in 2007, using two microscopes connected to a rail and ruler. A pictorial
description is presented below for both techniques. A comparison of the two sets of data showed an agreement
to within + or - 3 mm.
Below Rhoda, Jim and the staff at the IMSS, July 2007, reviewing and comparing the data in the literature and records on the lengths of IMSS 2427 & 2428 telescopes.
|In July 2007 we repeated
and re-checked our earlier measurements for the dimensions of the 2427 & 2428
telescopes at the IMSS with new equipment. We found that both of our data
sets are in good agreement and they continue to show serious
inconsistencies with those in the
The July 2007 repetition of our original 2005 measurements of the length of the Galileo's original telescopes using a new version of our optical ruler designed especially for this task of making the measurements from outside their cabinets. The optical ruler is composed of two microscopes with cross hairs. One microscope views the left hand side of the telescope the other the right side. They are connected with a centimeter scale.
Below are some photographs of the equipment and measurement process.
|Above: the cabinets containing the Galileo IMSS 2427 and 2428 telescopes with Rhoda and Jim literally on their knees measuring the length of IMSS 2427.|
|Above is the eye piece side of our optical ruler with their sliding focus tubes, one was used to view the left side of the telescope the other use to view the right end of the telescope. Their fiducial cross hairs were used to register the microscopes to the ends of the telescope. They are connected with a scale to make the length measurements.|
|The above photo shows the telescope side of the optical ruler. It uses two low power microscopes with cross hairs. The microscopes are pressed firmly to the glass of the cabinet making them perpendicular to the cabinet.|
Corrections had to be made to our measurements for 2428 because it was not parallel to the case. This amounted to a fraction of a millimeters in over all length. The two arrows show the rotated position of the 2428 which is above the arrows. The objective end of the telescope is pointed at the camera.
On Jim's 80 th birthday and after after completing the delivering of several of our replica's to the IMSS we with with Dr. Strano, curator of the IMSS, made one more fast measurement by a third technique of the length of the IMSS 2428 telescope.
We did this using a draftsman right triangle, a tape measure, and a few strip of black tape. It was a bit crude certainly fast and accurate to a few mm..
Again we very much thank the staff of the IMSS in Florence Italy for their help and patience during this projects especially Dr. Giorgio Strano Curator of IMSS who is on the left of the photos above helping with the measurements. The photo on the right shows the team including Rhoda getting data to correct for the angular displacement about the vertical plane of leather telescope.
result for the length of the Telescopes!
and science in action!
|Our measurements and their comparisons with the literature
were made with three types of apparatus described above on three occasions. We are reporting in this table our average measurements. Look above again to see us measuring the lengths of the original Galileo's Telescopes at IMSS in Florence Italy.
The focal length of 2428 objective (Ronchi 956 mm ref 6a) and (Greco etal 980 mm ref 7). The focal length of the eyepiece of 2427 (Ronchi-48.8mm) and (Greco etal-47.5)
|Source of data and telescope||
Telescope barrel length for IMSS # 2428
|826 mm 3 mm. one sigma corrected for typo error 12/05/08|
IMSS web site:
Telescope barrel length for IMSS # 2428
|835 mm. plus or minus?|
Total length for IMSS #2428
925mm. plus or minus 3 mm. corrected typo error 12/05/08
Total telescope length for IMSS #2428
|927 mm plus or minus? an updated value will be published on IMSS web site shortly12/05/08|
|STScI web site||now quote IMSS new data|
|Our measurements :
Total telescope length for IMSS # 2427
|1265 mm. plus or minus 3 mm one sigma|
IMSS web site:
Total telescope length for IMSS # 2427
|1273 mm. plus or minus
an updated value will be published on IMSS web site shortly shortly12/05/08
Bottom line on length: 12/05/08
IMSS has made new measurement for both telescopes that will appear on their
web site shortly.
The importance of these numbers for the total length is that when one uses the longer lengths and the focal lengths for the lenses published for these telescopes it is an optical impossibility for the telescopes to focus at infinity! If they are made to the published data the view of the planets and stars will be blurred out of focus images.
Another point using our measurements it is possible to use
the current lens without it present little holder which may also not
be original. Doing this one could use objectives lens that has
Ronchi focal length measurements of 956mm The end result is a telescope that
dimensionally does not have this out of style extra piece holding the
eyepiece and it will still focus at infinity.
A review; The distances between the eye piece and the objective lens, in a Galilean design, is calculated from the sum of the focal length of objective and and the focal length of the eyepiece. Remember that Galileo used a negative lens i.e., -47.5mm. so the values are subtracted. (See standard text book on optics)
Both IMSS and we, as partners in science, strive for accuracy in our
work. We understand that errors such as this can and will be copied over and over again
with repetition like a domino effect. They will even find their way
other publications to which people will look for good data on the Galileo
telescopes such as NASA's affiliate, STScI, which reports on Hubble data and identifies itself as "the Formal Education Group of the Space
Telescope Science Institute's Office of Public Outreach," see
The IYA impact of this dimensional difference for both Galileo's telescopes is that builders and enthusiasts will be absorbing these errors when they make there own copy of these very historical and beautiful telescopes for their IYA activities. If they use the longer dimension and published optics for the lenses they will find that their telescopes will not focus at infinity. They will not be able to replicate the Galileo observations that he made in 1609 and later.
It's not good for the "image" of sciences if we can't pin down how and where the image is focused for the worlds oldest, simplest, and historically significant telescopes, instruments we want to use as teaching tools for science.
On the other hand the process described above is an excellent example of science at work! It starts out with a problem, an anomaly, or inconsistency to resolve and one has to determine the most probable cause. Remembering Galileo's 1610 letter to the Tuscan court, substantial effort had to be spent honoring the first principle of science, that is, to be right. By searching the known data and making repeated measurements and with the help of other professionals in the field, we achieved consistent data. So replicas can be made that will be working telescopes capable of operating the way they did for Galileo and to serve as the teaching tool to tell the "truth" he wanted observers to see in the heavens The story of building Galileo's instruments is a classic example of how Galileo and his new methods of science can be brought into action.
ref. 6a V. Ronchi "Sopra i cannocchiali di Galileo," L 'Universo 4,791-804(1923)
ref 7 (Galileo) Greco, Vincenzo, G. Molesini, & F. Quercioli. Optical tests of
Galileo's lenses. Nature 358 (July 9, 1992) 101.
All photos and written material are by Jim & Rhoda Morris unless noted otherwise. Free personal and educational use and reproduction is encouraged; We would appreciate an acknowledgement. all commercial rights are reserved. copyright 07-07-2007 Jim & Rhoda Morris