Observatory Overview From The Director

On The Nature Of The Astrophysical Observatory

{ Abstracted from the document On The Nature Of The Astrophysical Observatory written by Professor Irving K. Robbins, College of Staten Island, CUNY }

Table of Contents

Of course, you probably have concern that the campus area within the NYC metropolitan area has "light pollution" (excessive or misdirected light) and you are correct. To improve astronomical "seeing" on the campus the observatory is located on the darkest part of the campus. It is true that with your naked eye you will not see a sky as pretty as a mountain or desert area on campus but with our telescopes, which gather from 400 to 1600 times as much light as an eye can, we can easily see many of the wonders of the heavens. For research purposes, the telescopes at the observatory will be equipped with CCD (Charge Coupled Device) digital cameras that capture images and put them into a computer. These CCD cameras effectively increase our telescope's area ten times (effectively our 16" telescope becomes a 51" one). All modern observatories use this state of the art approach to astronomical observing. A small telescope equipped with a CCD camera could pull an image of a faint galaxy out of the Manhattan skies during the full moon phase! Since the final image taken with these systems is in a computer we use can use "image processing" software to get rid of unwanted light and enhance the quality of the image.

The observatory has a dome which blocks some outside light, as well as, has a "red light" system. These precautions are all designed to give the observer maximum "night vision". Humans have very good night vision. In order to achieve night vision, light must pass through the pupil and be transduced by receptor cells in the retina. Messages sent from the retina to the brain and spinal cord begin reflexes which regulate the pupil's diameter. A fully dilated pupil lets through only about sixteen times more light than a fully constricted pupil -- hardly enough to account for the almost millionfold range of visual sensitivity. The bulk of the adjustment is done by the receptors. In the case of dark adaptation, that task falls mainly on the rods (about 120 million in each eye increasing in concentration from center to periphery). The photopigment in the rods breaks down on exposure to light and this, in turn, begins the signal that may eventually result in seeing light. Once broken down, the pigment has to be re-manufactured and stored in the rods (Vitamin A plays a role here). This resynthesis takes almost 30 minutes to get full night vision. The rods also account for the fact that red lights do not affect night vision since they are completely insensitive to the extreme wavelengths (we see these with the cones).

You might have experienced this so-called "Night Vision" effect in entering a movie theater during the day. You are at first blind but shortly you can pick out fine detail from your seat as your eyes adapt to the low level of light. It take about twenty to thirty minutes to achieve full night vision. Urban and Suburban dwellers rarely develop night vision because car lights and street lights keep us from reaching maximum sensitivity. They rarely notice the wonders of the sky. From the observatory people rediscover what our sky looks like. In fact, it is easier to learn the constellation patterns in our area because we can see clearly all the major stars that form the patterns. As mentioned above, the red lights in the observatory do not effect night vision and permit us to see what we are doing, similar to a photographer's darkroom.

When we look at images of various objects from the CSI observatory's telescopes we can use special filters to remove the main light rays of City lights which are mostly sodium and mercury lamps. For the Sun, Moon and Major Planets very little of the above precautions are necessary except for very fine detailed work since they are very bright objects. Many people are under the misconception that if they visited the Major observatories they would see these objects a lot better than at CSI. This is not true! Theoretical a telescopes ability to see fine detail (called the resolving power) is dependent upon the aperture (main mirror or lens size) of the telescope. We have for our main telescope a 16" diameter aperture at CSI. Because of the earths atmosphere Solar, lunar and planetary details are just as good at CSI as the larger major observatory telescopes! Large telescopes are actually built to observe the faintest of distant objects (galaxies etc.) because they gather more light (wider openings) then smaller telescopes.

There is more to good observing conditions than a cloud free sky. The atmosphere's freedom from moisture and dust is called transparency and causes us the most problems in this area. The atmosphere's freedom from turbulence is called "seeing" and causes problems all over the world. Good transparency or seeing is needed depending upon different types of astronomical observations. Faint objects demand good transparency, hence, large telescopes are built in places that minimize this effect. For detailed viewing one needs good seeing. Lunar, planetary and bright nebulas and stars do not require excellent transparency because we are dealing with bright objects. They are so bright that sometimes we have to use filters to cut back the light received in order to see details on the campus.

In general, on cloudless nights our "seeing" is pretty good, especially from September to May when we will do most of our research work. Over the years we have noticed that we do get exceptional days and these have given us the best views of our solar system and beyond. All of the "bad" atmospheric effects are minimized the closer one works the telescope to the zenith (the point directly over our head) and this will be the case for the major research projects. There are some "bad" lights on our campus that effect the depth of space we can penetrate out to. A few of these interfering lights have been corrected but a fairly large number need further changes and it is hoped this will take place so that the observatory can reach its theoretical potential for observing dim objects.

The dimensions of the observatoy are 24-ft. by 24-ft. with a 16 ft. diameter dome. The main optical instrument is a computerized 16" f/10 Schmidt Cassegrain Telescope described below. The observatory is linked via ETHERNET to a well equipped astrophysical Laboratory (in building 5N) known as the "warm room". The warm room/Observatory setup is because observatories have no heat (or air conditioning) and are designed to keep ambient temperatures for their equipment year round. Remote operations of the observatory from the warm room are for human comfort during the coldest days of the year . This past year days extremely cold enough to use the remote facility did not appear and heavily dressed astronomers ran the observatory drinking lots of hot chocolates.

We have installed a traditional observatory dome which is motorized and under the control of the main telescope operator. The dome is a universal symbol of astronomical work and has added a scientific ambience to the new campus. The new 12 foot Radio Dish should add to this image. One can see that the main telescope is attached to a custom heavy duty metal pier which sits upon a large mass (called an inertial foundation) which is not attached to the building. This arrangement will mean very steady viewing for high magnification work which promises us very spectacular views of the Sun, Moon and Planets, as well as, permitting meaningful research.

You can see from the figure that if you want to view the heavens directly from the main telescope you have to get up to an observatory deck. A curved spiral concrete stairwell from the door pictured brings one up to the deck (not seen in the figure). We installed a special electric lift that runs on tracks at the side of the stairs for wheelchair bound individuals so that they can get to the observation deck. As far as the author knows, this handicap access arrangement is unique in the astronomical world.

The 16" Meade Schmidt-Cassegrain astronomical telescope shown to the left is our primary viewing device. A 16" mirror is the main focusing device located within the telescope. The telescope is fully computer controlled with over 64,000 celestial objects in its memory. The computer gives us tremendous power. It permits very accurate alignments, as well as, rapid finding of celestial objects. This computerized locating ability permits us to view objects in our urban skies which would be otherwise very difficult if not impossible in previous generation telescopes.

This speedy technique of obtaining objects results in eliminating much of the time consuming mechanical drudgery that many people have experienced with setting up and operating astronomical telescopes. Even a novice can simply control the computer console to view an on screen sky map and with a mouse quickly find what they are interested in. A simple "click" and the telescope will go to the object of interest. In order to make this possible the telescope has to be aligned to a very high precision with the sky. The custom steel piers pictured in the previous figure will make this task very attainable. When lots of people want to view through the telescope, saving time becomes a premium. By finding objects quickly, the educational capabilities of this system are extremely enhanced.

The chosen Meade 16" telescope is the finest commercially mass produced telescope in its class for university research programs. For the planned laboratory and research work, some modification were a must. We have obtained the telescope from the "California Telescope Company" with the following modifications to ensure success for the observatory objectives.

1. As mentioned, the observatory was planned around the customized permanent steel pier that the telescope sits upon. The pier in addition to being massive is latitude and telescope specific.

2. Special software for local computer control of the telescope has been provided.

The recent electronic breakthroughs now permit small observatories to use equipment previously only available to major observatories that could afford very expensive equipment. As mentioned above CCD imaging systems capture images electronically and store an image in a computer to allow one to enhance it. Once we have stored images in our computer showing what we are doing, we are free to display them on high resolution monitors. We also have stored most images taken by NASA and the Jet Propulsion Laboratory. (Visitors who come during the day or on previously scheduled night that turns cloudy or rainy can still give get a presentation of magnificent views of our solar system and the universe.)

CCD images are many times more efficient than photographic films which results in markedly reduced exposure time. For example, a fast film used to photograph Saturn might require ten minutes but with CCD we do the same job in ten "seconds"! Most light pollution in our images can now be subtracted out. Even an out of focus image can be changed using image processing techniques. Faint details in images can be brought out by using a variety of coloring techniques in conjunction with mathematical methods built in to our image processing software. Positional and brightness data can be obtained via software. In other words, this system is an extremely smart "camera" for the observatory.

A major field of astronomical measurement that will take place at the Observatory is "photometry" which requires obtaining the brightness of a celestial object called its magnitude. The CCD camera systems we have, as well as, a dedicated photometric camera are designed to carry out this work. Many of our planned research projects require measurement of celestial brightness. Essentially the observer centers the object of interest into the Photometer instrument which is attached to the telescope and gets a reading on the objects brightness. The data obtained is then sent to the computer for data reduction which produces will known standard meaningful results from the raw experimental data.

Listed below with explanations (if needed) are 21 representative types of exercises to be undertaken with the portable systems and in some cases in conjunction with the CSI Astrophysical Observatory..