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10-Inch Siderostat-type Refractor Telescope

In The People's Observatory


Description: This is much more than a historic artifact. It is an operable piece of scientific apparatus that is as useful today, as it was when first installed in 1941. As with much older telescopes at the Allegheny Observatory of the University of Pittsburgh(these three telescopes, still in active use, date from 1912, 1906, and 1861!), telescopes never become obsolete!

The primary instrument of The People's Observatory is a 10-inch Siderostat-type Refractor Telescope, manufactured by the Gaertner Scientific Company of Chicago. This is the second largest operable Siderostat telescope in the world!

The largest operable Siderostat telescope, which includes a refractor telescope with a 15-inch objective lens, is installed in the Flower and Cook Observatory, of the University of Pennsylvania, in suburban Philadelphia. A much larger Siderostat telescope was demonstrated at a special exhibition in Paris late in the Nineteenth Century; after the exhibition, this telescope was dismantled and never reassembled!

The Siderostat telescope differs from other telescopes in one major way: the telescope tube never moves(except, of course, by the same motions of the Earth that move us all, at the same time!). Instead of moving the telescope tube, a flat first-surface mirror is used to reflect celestial objects from the sky into the telescope. However, since this mirror is flat, and the telescope gathers light with a 10-inch objective lens, this is a refractor telescope, not a reflector telescope.

To reflect objects into the telescope, a sidereal coelostat(i.e. "siderostat"), with an electric motor, moves the mirror north or south, in declination, and east or west, in right ascension. The switches on the control console include a slow-speed position for fine-tuning the observation. Once the object is found, a clock-drive motor allows the mirror(moving at the same rate of speed as the rotation of the Earth) to follow the object across the sky, so it continually appears in the telescope view.

In addition to large setting circles(for right ascension and declination) and motor controls, the control console includes a sidereal clock. As the apparent movement of the stars differs slightly from the apparent movement of the Sun(from which we derive our civil time), sidereal time differs from the time on normal clocks. Sidereal time must be used, in a simple equation, to determine the celestial coordinates for finding astronomical objects with the Siderostat telescope. In fact, except for the Sun, all celestial objects must be found using celestial coordinates, when using a siderostat telescope!

For nighttime observing, the public would use the Observer's Platform to look into the telescope at the object in view. The telescope was specifically designed to view objects in the southern sky, where the Moon and planets can be viewed. And, when the Moon and planets are in the proper position, they can also be viewed in the daytime sky with the Siderostat telescope. The Moon; the planets Mercury, Venus(often showing its phase, similar to lunar phases), Mars, and Jupiter(including cloud belts; but no Galilean Moons are visible in the daytime); and stars down to third-magnitude have been viewed by the public in the daytime using Buhl's Siderostat telescope.

When viewing the Sun, the public does not look into the telescope. The image of the surface of the Sun(including surface granulation and often sunspots) is projected onto a large, specially-constructed projection screen, for simultaneous viewing by all people in the Observing Room. The large circular projection screen includes two diagrams, which allows the public to compare the size of sunspots to the size of the Earth(many sunspots are larger than the Earth!).

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Often, Observatory observing sessions would also include a couple special demonstrations. When the clock-drive motor is deactivated, the public can see the object apparently move out of view. This demonstrates the rotation of the Earth. Actually, with the clock-drive motor deactivated, the telescope moves with the Earth until it can no longer see that particular celestial object.

During a solar observing session, the astronomer would place a piece of wood near the telescope's eyepiece(where the public would look into the telescope during evening sessions). The piece of wood would immediately start to burn! This, purposely, is a dramatic demonstration, to show the public, particularly children, why they should never use a telescope or binoculars to look at the Sun!

The People's Observatory is actually a fairly small space, on Buhl Planetarium's third floor, consisting of two rooms. The Observing Room(one-third of the Observatory, including the Observer's Platform) is where the public view celestial objects either by looking into the telescope eyepiece or by viewing the Sun on the projection screen. The Telescope Room(two-thirds of the Observatory) is where most of the telescope, and the siderostat motor unit, is located. The telescope is actually mounted so that it is in both rooms, with the tube going through the wall between the two rooms.

For the comfort of the public, the Observing Room is heated during cold weather. Unfortunately, the Observing Room is not air-conditioned, as is the rest of the Buhl Planetarium building[first public building(not commercial office building) in the City, and possibly the State, to be air-conditioned!].

The Telescope Room is neither heated nor air-conditioned! It was purposely built this way. Heat from the building would disrupt light entering the telescope, which would make viewing celestial objects very difficult. Hence, telescope rooms in all observatories are purposely not heated.

The Siderostat telescope was particularly installed in Buhl Planetarium, with children in mind. Children do not have to climb ladders, or strain their neck, when looking through the Siderostat telescope, as they often would for looking through telescopes in other observatories. And, when looking through other telescopes, often a child may accidentally bump the telescope, requiring the astronomer to find the object again. This cannot happen with the Siderostat telescope, since the telescope cannot move!

Jean Leon Foucault of France invented the Siderostat telescope. As he was a very sickly man, he died before he could construct a prototype.

Jean Leon Foucault also developed the Foucault Pendulum, which demonstrates that the Earth rotates on its axis. A beautiful brass and marble pit for a Foucault Pendulum was constructed as part of Buhl Planetarium's Great Hall in 1939. Although Buhl's original Foucault Pendulum(which is also the property of the City of Pittsburgh) is currently in public display at The Carnegie Science Center, it is our understanding that it will be returned and will again demonstrate an important astronomical principal at the Pittsburgh Children's Museum and Center.

Looking through a fairly large telescope in an observatory has always impressed visitors to Buhl Planetarium. Children would be amazed with their first live views of the craters on the Moon or the rings of Saturn, with the Siderostat telescope; video images or photographs cannot compare with actually looking at a celestial object through a telescope. Even teenagers, who would come to Buhl Planetarium in the evening to see a laser-light show and did not expect to look through a telescope, were quite impressed with, often, their first telescope experience!

History: The People's Observatory opened on the third floor of The Buhl Planetarium and Institute of Popular Science on November 19, 1941. Famous Twentieth Century Astronomer Harlow Shapley, at that time Director of the Harvard College Observatory, gave the keynote address at the dedication of this Observatory and the 10-inch Siderostat-type Refractor Telescope.

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The People's Observatory was constructed at a cost of $30,000(1941 dollars). Although the design specifications met research observatory standards, it was primarily designed for use by the public, hence the name The People's Observatory. Although little research has been carried-on at The People's Observatory, the Observatory's primary telescope was used to assist in the improvement of maps of the Moon's South Polar Region in the 1980s.

"First Light" through Buhl's Siderostat telescope was the ringed-planet Saturn. This was the first celestial object viewed by the public with this new telescope.

An interesting historic anecdote: On the same evening of the Observatory dedication, Buhl started a new Planetarium Sky Show and opened a new gallery exhibit. The Sky Show, regarding Celestial Navigation, was titled "Bombers by Starlight"(Buhl provided Celestial Navigation classes to many military servicemen, during World War II). The new exhibit, in Buhl's lower-level Octagon Gallery(which encircles the planetarium projector pit, below the planetarium theater) was titled "Can America Be Bombed?" This exhibit opened two and one-half weeks before the Japanese bombed Pearl Harbor, Hawaii!

Public observing sessions, in Buhl Planetarium's People's Observatory, ceased with the last session on the evening of August 31, 1991. Among other celestial objects, the public viewed the planet Saturn that evening, which had also been viewed at the opening of the Observatory in 1941. With the opening of the new Henry Buhl, Jr. Planetarium and Observatory in The Carnegie Science Center, on October 5, 1991, the original Buhl Planetarium assumed a new role.

The Carnegie Science Center had originally been constructed without classroom space, as it had been decided that all Science Center Science and Computer classes for children would continue to be taught in the original Buhl Planetarium building. Hence, from then on, both the Zeiss II Planetarium Projector and the 10-inch Siderostat-type Refractor Telescope were used for teaching Carnegie Science Center children's Astronomy classes. This lasted until February of 1994, when the Buhl Planetarium building was completely closed; the building and all contents were returned to the City of Pittsburgh in December of 1996.

More information on the 10-inch Siderostat-type Refractor Telescope and The People's Observatory can be found on the Internet at URL:

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Two Proposed Options --

Proposal I: This is our preferred proposal. The 10-inch Siderostat-type Refractor Telescope would be kept in The People's Observatory, on the third floor of The Buhl Planetarium and Institute of Popular Science, and used for astronomical demonstrations for children and other patrons of the Pittsburgh Children's Museum and Center.

The plans for the Pittsburgh Children's Museum and Center illustrate a connection between the third floor of Buhl Planetarium and the third floor of the "Nightlight Building." Hence, since the "Nightlight Building" will include an elevator, The People's Observatory would now be handicapped-accessible for solar observing sessions.

A means for allowing wheelchair patrons to reach the Observer's Platform(three steps higher than the Observing Room floor) would have to be found for evening observing sessions to be completely handicapped-accessible. Since the difference is only three steps, we would seek such a means, which we anticipate would be of reasonable cost.

We note that the architect's plans included with the Lease Agreement, between the City and the Pittsburgh Children's Museum and Center, include no alternate plan for The People's Observatory. There is probably a

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very pragmatic reason for this. As the Observatory is really a pretty small space, it would not be cost-effective to add heating and air-conditioning to this space, as would be necessary for any other use(other than, perhaps, storage).

Volunteers from Friends of the Zeiss could operate the Siderostat telescope for public viewing. Friends of the Zeiss would operate the telescope as a supplement to the Children's Museum's programming. If there is the interest, staff and volunteers of the Pittsburgh Children's Museum and Center could also be trained to

operate the telescope. However, we would not expect Children's Museum staff or volunteers to operate this instrument.

We are seeking paid consultants to assist us with getting the Siderostat telescope, and its motors, operating after eight years without regular maintenance. Of course, it would make a lot of sense to have technicians, who have worked on our Siderostat telescope, do this work. However, these technicians now work for The Carnegie Science Center. Since The Carnegie Science Center management wants Buhl's Siderostat telescope not to operate, it would be very difficult for any of these technicians to help us.

There are a couple of people, who have worked on the Siderostat telescope in the past in a volunteer capacity, who would be willing to assist us as volunteers in the telescope's maintenance. Once the Siderostat telescope is running again, a schedule of regular maintenance should ensure continuing operation at a very reasonable cost.

We anticipate that, from time-to-time, a major part may fail in the machine. Then we would need to have a new part fabricated specifically for this instrument. Having this done is nothing new or special. Other historic operating equipment in the region, including the machinery that operates The Duquesne Incline, has had the same problem. The Duquesne Incline has a couple very good machinists, which they work with, when there is a problem with their equipment. These machinists have expressed a willingness to work with us, when the need arises.

Should the Siderostat telescope be removed from the Buhl Planetarium building, it will not be displayed. It would make no sense to display an unusable telescope, in The Carnegie Science Center or elsewhere. Considering the cost of erecting a new observatory, with special requirements, for the Siderostat telescope, it likely will remain in storage forever!

Proposal II: The 10-inch Siderostat-type Refractor Telescope would be kept in its original installation in The People's Observatory, on the third floor of The Buhl Planetarium and Institute of Popular Science, in a

"mothballed" condition. We would maintain the telescope, in a "mothballed" condition, until such time that use of the telescope was agreed-to.

Such a "mothballed" condition would not preclude the use of the Observatory, by the Pittsburgh Children's Museum and Center, for other purposes, provided the Observatory is not modified in any way to preclude future use of the telescope.

Use of the Observatory for other purposes would probably be limited, since one-third(Observing Room) of the Observatory is heated, but not air-conditioned, and two-thirds(Telescope Room) of the Observatory is neither heated nor air-conditioned. The Observatory could certainly be used for storage, without adversely affecting the future use of the Siderostat telescope. Even when Buhl was open, and the telescope was in use, part of the Telescope Room was used for storage.