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Arkansas Sky Observatories' 100,000 Milestone

by P. Clay Sherrod

Arkansas Sky Observatories will reach it's sixth decade of serving science
through research, publications and teaching in March, 2021,
becoming one of the world's oldest active and contributing observatories worldwide
that is completely privately funded for its research and activity.

During the morning of June 8, 2017, Arkansas Sky Observatories' Petit Jean Mountain South facility - H45 - reached a milestone.  At 09:37 Universal Time, its precise measurement of the position and magnitude of the Near Earth Object asteroid 2017 HY50 resulted in the 100,000th astrometric measurement of comets and minor planets for the International Astronomical Union's Minor Planet Center.

The Legacy of Arkansas Sky Observatories

Founded by P. Clay Sherrod in 1971, the first principal focus of Arkansas Sky Observatories (ASO) was the study of Mars during its very close opposition in that year of the planet Mars.  The subtle surface and atmospheric changes noted throughout the close approach resulted  in the desire  to concentrate studies of celestial objects of change:  the planets Mars and Jupiter which demonstrate very pronounced changes over time, the motions and orbits of asteroids and comets, and cataclysmic stars - novae, supernovae and variable stars of irregular activities.  Located in the then-dark skies near the North Little Rock, Arkansas airport north of the city, volunteers at the two observatories were instrumental in the actual determination of the rotational period and shape of the large asteroid Eros (433).  The Observatories became well known worldwide for its contributions in the studies of planets, comets and variable stars.

Clay Edigewood1974s

Sherrod at ASO's Edgewood Observatory - North Little Rock Airport location, 1974
Late in the evening on night in 1974 after the public fury of the fizzled fate of Comet Kohoutek had been forgotten, the phone at ASO's Edgewood Observatory rang unexpectedly as I was sketching details of my views of the planet Jupiter in the telescope room next door.  We had no cell phones, no fax computers.  Just an old black desk phone which served us well.

"Um, ...Clay Sherrod?" the distinct voice with British accent asked somewhat apologetically.  The poor quality of the call told me that it was long distance
"Yes, this is Clay Sherrod," I replied.
The voice continued somewhat excitedly without much explanation:
" see....this is Brian Marsden from the Harvard-Smithsonian Central Bureau of Astronomical Telegrams [CBAT], and we have something you have clear skies tonight?"  he asked.  "I wonder if you might check and see if there is a comet about."

Where did he get my name, my phone number I wondered, but there was some inherent honor in hearing from the Harvard-Smithsonian Observatory I thought.

Dr. Marsden gave the the celestial coordinates of a suspected faint comet that had been discovered and provided what he thought might be the apparent direction of motion and wanted me to confirm as to whether the discovery was real or spurious.  There was no comet anywhere near that position and my follow-up call was met with great appreciation and gratitude from this gentleman whom I had never met nor spoken with until that unexpected phone call.

Brian Marsden refractor  Marsden at the Harvard Refractor shortly before his death in 2010.

Thus began an active role in verification of reported celestial events - new comets, asteroids, novae and supernovae.  The small Arkansas Sky Observatory became one of about a dozen "stations" as he called them, worldwide - each selected he later explained so that any two of them had a good chance of having a clear sky when needed.  Over time, as ASO continued its studies of celestial transient phenomena, growing to  a complex of several observatories throughout the state of Arkansas, Dr. Marsden's career as a leader in the studies of comet and minor planet orbits and origins reached the pinnacle of achievement and he became a world leader in the subject.

Our relationship and contact continued weekly and sometimes daily until his untimely death on November 18, 2010.  Dr. Brian Marsden became my mentor and closely guided me as my career in science and astronomy grew.  He served as my academic advisor and guided me through my advanced education in astronomy, and always remained a close friend throughout a period of nearly 35 years.
Old School Astrometry - Mathematics and No Sleep

A  brief academic counseling session with Brian Marsden a couple of years later led to my understanding and hands-on use of astrometry - the precise measurement of any celestial object - a tool vital for determining the orbits of comets and asteroids as they orbit the sun.  In the 1970's there were very few known asteroids, or minor planets as astronomers prefer to call these celestial rocks.  Today, the number of known minor planets number in the hundreds of thousands, most of which are "main belt" or big chunks of rock that orbit within the asteroid belt between Mars and Jupiter and maintain fairly stable orbits.  Among those is minor planet 117736 Sherrod, never a threat to anyone.

However, in addition there are tens of thousands classified as Near Earth Objects, or NEOs, that have the potential to intersect with the orbit of the Earth at some point in their trips around the sun, and thus there is a potential for impact of Earth by those objects.

Although computers had begun their development and rise to power in the 1970's, there was very little use for astronomical purposes outside of testing and development; the measurement of moving objects in the sky - comets as well as NEOs - was done the old school way:  by hand and the power of mathematics.  The first step in orbital determination is to accurately plot the object at a very precise moment - accurate TIME is of the essence with each observations.  Of course, unlike 150 years ago when rather inaccurate positions were measured at the telescope visually, we relied on photographs from which the comet or asteroid would be measured as it moved across a field of fixed stars.  At least three photographs were required in order to obtain a proper orbital determination, the three plots necessary for determining an arc, rather than a straight line of motion.

Unitron film camera The Unitron 3" x 5" sheet film camera used at ASO for astrometric measurements

Unlike the speed and ease of today's CCD and digital cameras which can utilize rapid computerized "plate solving" software to very precisely place the exact right ascension (east-west) and declination (norht-south)
position of an object in less than two seconds, we needed to use photographic glass plates (preferred) or large format sheet film that could be placed onto a light box and carefully measured.  Since ASO and its projects was a totally private and in the strictest sense non-profit, I was forced to rely on sheet film in a primitive Unitron 3 x 5 sheet film camera, loaded and unloaded in the dark,  one piece of film at a time after the long exposures were taken, usually a minimum of 45 minutes, carefully guided through one of the observatories' telescopes.

The three sheets of film would have to be processed, then completely dried before loading onto the light table for measurement.  Once properly prepared, the tiny image of the moving object (comet or asteroid) would be carefully compared against the positions of  THREE fixed stars as determined from the (now obsolete) Smithsonian Astrophysical Observatory Star Catalog, a voluminous 4-book set of numbers.  Triangulation from those stars to the moving object resulted in a rather precise position of the object which was then forwarded by MAIL (or relayed by phone) to Marsden at the CBAT.  The measurement of ONE OBJECT required a full night and much of the daylight morning following.

measuringLightBoxS  The old school method of measuring a comet or asteroid from film.

Today, using sensitive CCD astronomical cameras which can reach magnitude 20.4 in the ever-increasing lighted skies of Petit Jean Mountain, and computerized plate solving programs (Charon, from Project Pluto - Bill Gray) it is not uncommon for me to obtain over 200 measurements in ONE NIGHT.  All are recorded in sequence on the computers and with one push of a button a complete report of all measurements of all objects are sent to the IAU Minor Planet Center.

Milestone at the Push of a Computer Key

Rather than the typical 150 or 200 observations on the morning of June 8, 2017, I was only able to obtain 73 measurements due to clouds and the full moon in the sky.  When the moon is out, its light pretty much blocks all of the faint objects from view, but on this night were some potentially hazardous NEOs flying about and I was able to obtain that small number.  Among them was the asteroid 2017 HY50, rated as a potential impactor at this time, and one of the six measurements of this celestial rocks provided one of the most important milestones of ASO's illustrious career in astronomy:  it was the 100,000th measurement submitted to the Minor Planet Center by ASO in its 15-year stretch of digital measurements; the number did not include all of the laborious hand-derived measurements from the 1970's through 1990.  From 2002 to June 8, 2017, Arkansas Sky Observatories logged 100,033 measurements submitted.  Unfortunately this number represents ONLY those since digital recording began - 2002 - and not those laborious measured by hand prior to the advent of digital astronomy.

Although there are computerized robotic sky surveys operating today that take all-sky shots nightly and provide in some cases quite inaccurate measurements of masses of moving objects via computerized plate solving of large chunks of sky, ASO - with its modest equipment by comparison - still isolates on each and every object individually and carefully measures its motion exclusively.  These sky surveys surpass millions of observations, but the precision needed to really pin down the orbits of the comets and asteroids comes from individualized precise measurements from several dozen stations such as ASO.

In terms of numbers, the 100,000 mark by ASO may seem pale in comparison to the publicly supported "big guys", but it is the most measurements contributed to date by any privately funded (no grants or public funding of any sort) observatory worldwide and I am quite proud of the progress made by the seven observatories associated with the history of Arkansas Sky Observatories.

100k  From ASO: (

The screen shot (above) shows the summary of he MPC report for June 8, 2017 on which the 100,000 milestone was reached by ASO.  This page (see URL above for direct access) is accessible by any person visiting the ASO website ( and will reflect the nighty, monthly, yearly and total observations to date.  Another feature of the Astrometry tab on the ASO website is that any OBJECT (comet or asteroid) can also be accessed to examine ALL observations of that object since 2002; the MPC "packed format" designation must be used however to access those objects.  This page of astrometric observation is used by astronomers worldwide on a daily basis.

In addition to daily reports being sent to the Minor Planet Center, ASO serves to provide astrometric observations for updates and special projects by NASA, the Jet Propulsion Laboratory, Arecibo  Radio Telescope, Goldstone, the Oriental Astronomical Association, Lockheed-Martin, and many other public and private enterprises.
Moving Past 100,000

The future of Arkansas Sky Observatories will continue to include the studies of small bodies of the solar system in addition to other scientific research in astronomy as well as paleontology, archeology, geology and environmental sciences.  That being said, sadly I admit that there will likely not be a 200,000 milestone if you simply run the numbers against the age of the ASO founder and operator to the amount of time required for such studies.  Perhaps out there is some young, bright protege who may be willing to learn the focus, philosophy and challenges that have always been the hallmark of the Arkansas Sky vision.

One thing I am certain of:  I can say without hesitation that I am very proud of the accomplishments of Arkansas Sky throughout the past 50 years, through its teaching, publications ( ) and outreach throughout the scientific and educational communities.  Few people can truly say that they have lived the dream that they imagined as a child.  The success of Arkansas Sky Observatories and its programs has fulfilled all of my expectations of life.

PCS, 2017
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