Extracted by Permission from
"Electronic Imaging in Astronomy; Detectors and Instrumentation"
by Ian S. McLean
Professor, Physics & Astronomy, UCLA
ISBN 0-471-96972-9, Praxis Publishing, Chichester, UK, 1997:  order from publisher only
http://www.praxis-publishing.co.uk
  
     All astronomers speak about "going observing", but what does this mean? If you are an
amateur enthusiast then it may mean going no further than your back yard or your local
astronomy club to use a telescope to view your favorite objects. For professional astronomers
however, the phrase means much more. Implicit in the phrase is the fact that to understand the
Universe we must observe it, and to do so we will need more than our human eyes, more than a
telescope in the back yard. We will need all that modern electronic technology can offer. The
largest ground-based telescopes in the world are located at relatively remote, pristine sites, high
above sea level where the air is thin and the skies are astonishingly clear   so "going observing"
can also mean going far away from home. 

     Access by professional astronomers to national ground-based optical/infrared
observatories, as well as at most university or privately owned facilities, is on a highly
competitive basis. To obtain an allocation of "observing time" an astronomer must submit in
writing a well-argued scientific case for permission to carry out his or her observational
experiment. Deadline dates are set typically twice or three times per year. Selection is done by
peer review, that is, by a committee formed from the body of scientists who actually use the
facility. Unfortunately, all of the major telescopes are heavily oversubscribed, so disappointment
is a fact of life. To maximize the progress of scientific experiments at each facility, and to make
the optimum use of weather conditions, the astronomical community world-wide is expending
considerable effort on technology. As we shall see, this means highly-automated observatories
with much reliance on well-engineered instrumentation and computers, and it also implies new
cost-effective solutions for the design and management of telescopes and measuring equipment.
  
     Observing time on large telescopes is therefore difficult to obtain and is very valuable; it is
important that no time be wasted. Also, since the telescope and instrumentation is quite complex,
guest astronomers who may visit the observatory only twice per year cannot be expected to learn
the myriad of operational details. To solve this problem all large observatories provide one or
more highly-trained personnel to support the visitor. Usually a Night Assistant/ Telescope
Operator is provided; he or she will be responsible for control of the telescope and dome,
ensuring efficient operation, keeping an observatory logbook and the preparation of observatory
equipment. The night assistant has the final word regarding safety matters such as closing the
telescope dome if the wind speed becomes too high. Sometimes a Support Scientist, who is a
professional research astronomer on the observatory staff familiar with the application of the
instrumentation in question, is also available to assist first-time or irregular users of the
observatory.
  
     A guest observer (or G.O.) planning to use a modern, computer-controlled electronic
imaging camera or spectrograph at one of these major facilities might encounter the following
pattern of work. The visiting astronomers will probably arrive by air a few days before their
allocated time to ensure that they are not travel-weary and to discuss their plans with observatory
staff. They may have traveled from North America or Europe to Mauna Kea, Hawaii, or from
Europe and North America to Chile or Australia, or any of several other destinations. By
mid-afternoon on the day of the first night on the telescope, the observatory staff, which may
include the support scientist and an engineer experienced with the system to be used that night,
will be in the telescope dome making sure that the telescope control system and the instrument
are both functioning correctly. The visiting astronomer(s), often including graduate students
receiving training in observational methods or seeking data for a thesis topic, may well elect to
be present for these checks, and may wish to practice using the instrument. This may mean
becoming familiar with a control panel, or with the operation of a computer console on which the
experimental modes can be displayed and changed by typing at a keyboard. To feel confident
that they understand the operation of the instrument, the visiting astronomers will carry out some
tests of their own such as a "noise check" on the detector, or a calibration image or spectrum; all
of these terms and procedures will be described later.  With everything in readiness for the
evening, they return to the observatory residential lodge where a meal is prepared for them. This
is usually a great chance to meet people from all over the world, and the dinner conversation is
often buzzing with astronomical jargon! Between one and two hours prior to sunset the
"observers" go back to the telescope dome, usually in the company of the night assistant, to
complete their preparations. This entails discussing the "observing plan" with the night assistant,
providing him/her with a list of object names and positions or "coordinates" in the sky which get
typed into the telescope "control" computer, and taking some important calibration data such as
"dark" frames with the detector covered and "flat fields" or "arc lamps" which are exposures
using special artificial sources (lamps).
  
     As the twilight fades and the sky becomes dark enough to commence work, the night
assistant will "call-up" the first object on the target list and a computer will instruct
electrically-driven motors on the telescope's rotation axes to move or slew to that position.    
Using a special TV-type camera at the focus of the telescope, the guest astronomer examines the
field of view to confirm that the telescope is pointing at the object of interest   usually by
reference to an existing star chart. Sometimes of course, nothing can be seen because the
object(s) are too faint and require a long exposure; in that case the field must be confirmed by
checking the pattern of brighter non-target objects in the vicinity. When the object is correctly
centred, the observation begins. Having put the camera or spectrograph to the required settings
by typing command words or letters into the "instrument" computer (rather than the telescope
control computer), all that is required next is to issue a "start" command. The total time for which
the measurement lasts is called the "integration time" and this may be anything from a fraction of
a second to hours depending on the brightness of the object, the efficiency of the instrument plus
detector, the wavelength, and the nature of the experiment. If the integration time is fairly long
then it is essential to ensure that the telescope continues to track the object very accurately. In
principle, this can be done manually by viewing the object or a nearby star with the TV camera,
and pushing buttons on a "hand-set" electronically connected to the telescope drive motors in
such a way as to counteract any drift of the image. More likely, this action which is known as
guiding, will be performed automatically by the telescope control computer which analyzes the
image of the guide star on the TV screen, computes any motion and issues a correction to the
drive motors of the telescope. When the exposure is complete the image or spectrum will be
displayed on a  computer screen, an adjustment to the setting of the instrument might be made
and another exposure started. Meanwhile, some rapid analysis of the first result is undertaken
using the observatory computing facilities. Analysis and display of the measurements the
moment they are obtained is crucial to the optimum use of telescope time. The same pattern of
work is used repeatedly throughout the night.
  
     The night can be long, from before dusk until well after dawn, typically twelve hours
non-stop. Considerable concentration and often a degree of patience is required   sometimes the
latter is in relation to the other observers rather than with the experiment   and so some
sustenance or "night lunch" might be taken "on the job". Some look forward to opening up the
little brown bag collected at dinner, others would just as soon not watch! Depending on how
smoothly the experiment has progressed or on what has been found, tactical decisions may be
required to optimize the use of the night. Certainly, as dawn approaches, an extra effort is made
to get the most out of the remaining time. A golden rule of observing, which many newcomers
forget to follow, is to assume that "every night is your last" and never leave a crucial
measurement or calibration until tomorrow. Finally, with the last exposure complete, the night
assistant is given the go-ahead to close the dome, a few more calibration frames are made and
then the mirror covers are closed and the telescope is returned to its parked position. At last the
equipment is shut-down or placed in standby mode, logbooks or fault reports are filled-out, and
the weary group rally round for the walk or drive back to the lodge. The observers sleep until
early afternoon and then rise to prepare and review for the next night. Several days of this
activity constitutes the "observing run". The visitors will then spend a few days at the offices of
the observatory perhaps to obtain copies of their data on magnetic tapes, discuss their
observations with observatory staff and then fly back to their home institute to analyze the
astrophysical content of their data in detail and write a scientific paper.
  
     If you plan to use single dish radio telescope facilities then you may well follow the same
pattern as optical and infrared astronomers, particularly for sub-millimeter observations.
Interferometer and aperture synthesis telescopes such as the Very Large Array (VLA) near
Socorro, New Mexico are too automated to have visiting astronomers present for interactive
sessions. Usually one submits an "observe" file and the observations are taken as part of a larger
preprogrammed sequence. It may however be necessary for the astronomer to visit the facility
during the data analysis phase to make use of computers and software not available at their home
institute. Of course, the same process of competitive application for telescope time based on
scientific merit is used. 

     A similar situation is also encountered for telescopes located in space. While it may be
necessary to visit the "home" institute of the satellite, such as the Space Telescope Science
Institute in Baltimore or the ST-European Coordinating Facility near Munich, in the case of the
Hubble Space Telescope, it is rarely necessary to visit the ground-station and operations center.
Time on the Hubble Space Telescope and many other satellites is very competitive and is
awarded in cycles on the basis of scientific proposals reviewed by a peer committee. Once again
when time is awarded it is necessary to submit a detailed observing request that is programmed
into a larger sequence by observatory staff. You will definitely not get to "play" with the
telescope! Often, your data will simply arrive in the mail on magnetic tape and usually in a
reduced form ready for you to begin scientific analysis.

     Of course, there are numerous privately-owned observatories throughout the world,
mostly associated with universities and research consortia. Some of these facilities are quite large
and others are fairly small. At many of these places there is a much greater degree of "do it
yourself". Nevertheless, the pattern of preparation and work is essentially the same.

     Whatever the circumstances, professional astronomers usually work in the comfort of a
warm control room, rather than in the darkened telescope dome or the open air, while electronic
imaging devices and computer systems gather data. Occasionally, forays are made into the chilly
mountain air outside to check on the weather, or as in my own case, simply to look up at the
star-studded canopy of the night sky, marvel at its awe-inspiring beauty and remind oneself that
this is what it is all about!