SOUTHERN ASTRONOMERS and
AUSTRALIAN ASTRONOMY
ASTROMETRY and TRANSIT TELESCOPE
at
SYDNEY OBSERVATORY
The following page is based on my guest speaker
lecture that I gave several years ago to then the British
Astronomical Association (B.A.A.) New South Wales Branch meeting,
that was based on the once functioning large transit telescope at
Sydney Observatory. I also gave a demonstration with the transit
telescope, which is missing from this — but this will be added
when I get some more images next time I visit Sydney Observatory.
By Andrew James
Update : 30th March 2012
Figure 1 : Old Entrance to Sydney
Observatory. This shows the
‘old’
front entrance of Sydney Observatory (1981). Note the transit
instruments slits. The one on the right is where the present transit
instrument is placed, while the old slit has been covered by the
doorway. The alignment hole lies at the bottom of the right-hand slit
covered by a cream painted piece of metal.
Sydney Observatory : 1972
Recollections of Sydney Observatory
When I was young, probably somewhere between the ages of eleven
and twelve, I was fortunate enough to have been given a conducted
tour on one of the public nights through Sydney Observatory.
During 1972, as still is the case today, you could not visit this
once functioning observatory without an appointment for nighttime
viewing. To attend one of these nights, you had to book several
months in advance, which required a phone call to arrange. After
giving your general details and address, a letter would arrive
several days later confirming the visiting date and time of. The same
card was enticing, and stated you should come irrespective of the
observing conditions. If cloudy, there would be alternative
presentations.
Figure 2 : Sydney
Observatory
Entering Sydney Observatory
If you arrived at Sydney Observatory in the early 1970s, you would
have found the visitors entrance along the south side of the
observatory and right next to the unusual slit of the main Transit
Instrument. This is different from today, as the entrance is now on
the south-side of the building. To get to the door, you had to follow
the gravel path to the rear car park, and then turn into a narrow
bricked path that passed close to the stone pyramid, more
correctly known as the thermometer shed that is over the
marker and the stone of the trigonometric survey marker.
The entrance of the doorway then was marked by some very well worn
slate steps, which in central parts of both the third and last steps
had worn down right to the sandstone.
(See Figure 1.) Looking at the steps today, they have again been
repaved since the observatory’s recent
refurbishment. Illuminating the pathway, but more exclusively
directed toward see the dark grey steps, was a overhead light that
looks like it was probably designed in the 1920s, sitting on the
overhanging roof above the porch. However, this entrance has not
always existed.
Originally this was part of the second slit of the transit room,
where for a short time they once operated in tandem two transit
telescopes. By late-1888, the then New South Wales Government
Astronomer, Henry Chamberlain Russell (1836-1907) had reorganised the
transit room to be divided — and this partition still exists
today. This leaves the present transit telescope with the western
slit becoming the older entrance. This change occurred after
the installation of the 11½-inch f/13 Schröeder telescope
in the south dome.
After Mr. Russell had returned from Paris from the international
conference undertaking the enormous Astrographic Catalogue project.
These modifications became the observatory side entrance that I
passed through as a child. I have assumed this passageway was
designed so that visitors did not have to pass through the transit
room while visiting the south dome. Yet the present roof, and above
this door, still shows the position of this older slit.
The Anteroom of Sydney Observatory
To enter the building, you had to push a doorbell that they surely
was designed in the earlier 20th century. Frequently, if my memory
serves me correctly, it did not work very well. At the designated
time, the night assistant then greeted you, but this time on my first
visit it was by the Assistant Government astronomer, later Government
Astronomer, the late W.H. (Bill) Robertson. To the left of the
entrance, was a huge old government bound book, with a well weathered
spine, for all the visitors to sign. Usually, the first words was a
request to sign this book. The next thing you noticed, was the musty
air upon entry. This always seemingly highly traditional and noble,
giving the impression of a well-used institution steeped with an
interesting history — leaving the feeling that if
“the walls could
talk.”. At that time, you would then
notice the small anteroom, which was decorated on all the walls with
any old photographs in dusty frames of the southern sky —
including the montage of photographs of all of the previous N.S.W.
Government Astronomers. A small brass telescope sat on a small table,
whose origin was once from the defunct Parramatta observatory. Also
contained in this small area was an elegantly old-style celestial
globe, dated to 1791, the 1820s 3¼-inch Troughton Transit
Telescope, and the two tall ticking clocks made in
1820’s — again, all from Sir
Thomas Brisbane’s Parramatta
Observatory. For a time, most of this equipment was stored at the
Powerhouse Museum, though these days it is lock
behind glass on display after some much needed restoration.
To the far left were the narrow stairs that lead to the
observatory’s second level and the
telescopes south dome. The door directly ahead leads into the
astronomical office containing many astronomical books and
catalogues, placed in sumptuous bookcases. Here they often crowded
two large desks with books and paperwork, and here, the primary
reduction and calculation work of the observatory was made. (Later
when I was on the committee of the BAA. NSW Branch, this was used for
the group’s committee meetings,
typically commencing one hour before the general meeting.)
To the right was another door, which was nearly always closed,
that lead directly to the transit room. At this time it was always
dim, poorly lit and dusty. To young eyes, it appeared too wondrous,
an echo of the astronomical past. Most visitors took little notice of
this room — or even pondered its use — as they still do
today. For me, I still pause here for several moments pondering the
memories of the now distant past. For all the arriving visitors, the
night assistant did not usually include the transit room on the
nights’ agenda. However, there was the
most enticing sound from the transit room, with the sound of
incessant clicking of the clock hidden in the room.
The picture of the transit room is very different today, but it is
still recognisable from the Observatory photographs like by C.
Bayliss in “Town and
Country” on the 13th November,
1897, and some of those that still exist today that were also taken
by Russell.
Some of the fraying ropes, desks and cedar shelves cannot be seen
there today.
‘Screwed-in’ circular rope loops attached the ropes that
partitioned the north-south slits and opened either all, or just one
slit. The hooks on long wooden rods, like some used on the old
sailing ship of the 18th Century, hung in circular rope loops; either
near the transit telescope, or stood angled against the walls. Some
chronographic drum parts (dated to 1920, and made by Sir Howard Grubb
and Sons.) and the associated electrical wires either are not there
or have been trimmed down, especially around the table that once held
the chronograph drum. Also missing, placed in storage for safe
keeping, is the position or transit micrometer, it was at this time
was always placed in the rear of the transit telescope. Surrounding
the micrometer was the wiring that electronically placed marks on the
chronograph drum (or recorder), timing each of the transit events.
They conveniently attached these wires under the old traditionally
designed carpet, where a small worn ridge had been made a visible
impression.
Outside the observatory very little has changed. Since the
observatory change into a museum and for the badly need renovations,
the transit telescope has been painted, and the transit room has had
a new coat of paint. However, they have now relegated the magic and
romance of the transit room succinctly to the distant past.
Early History of Astrometry
The first astrometric measures were made by the Babylonians, but
it was not until Hipparchus that a serious observation program of the
stars and planets was undertaken. Hipparchus contributions made
immense advancements into the science of astronomy. [1]
Unfortunately, His observations and reputation in regard astronomy
were considered, even in his age, as brilliant. Today, even the most
ardent critics do agree, he remains he true Father of Astronomy, or
at least the greatest astronomer of antiquity.
We know that Hipparchus built the first observatory on the eastern
Mediterranean island of Rhodes, equipped with suitably accurate
instruments to measure the planetary and stellar positions. Our only
information on these instruments and his measurements are from
Ptolemy who briefly mentions that Hipparchus between 146 and 126 B.C.
made most of the observations We have accredited five major
discoveries to him.
a) He further developed the branch of mathematics
known as trigonometry, which allowed calculations on geometric
figures, especially with two and three-dimensional objects, that
includes the circle and the sphere.
b) He also developed extensive observations of the
planets and the stars, producing the first star catalogues which we
believe was inspired by a new star in 134 BC in the constellation of
Scorpius and a bright comet. Ptolemy later used Hipparchus
observations in his catalogue of stars, which he simply updated 270
years later. [2] We believed 129 BC completed this work, and the
catalogue listed 850 stars. Classification for each star was based on
their magnitudes, close to the modern one. Positions were calculated
very accurately, reported in terms similar to the latitude and
longitude on Earth. This catalogue was also used by Edmund Halley
1,800 years later.
c) By using the observations of the past, slow changes
in the star positions were found, and by this he discovered what we
now call the Precession of the Equinoxes. By his own
catalogue, the bright first-magnitude star Spica appeared 6°
from the autumnal equinox or the point where the sun crosses the
celestial equator, from the north hemisphere to the south. A previous
astronomer Timocharis of Alexandria had measured this value as
8°, some 150 years earlier. Hipparchus correctly deduced that it
was movement was not due to the star Spica but it was the east-west
movement of the Earth’s axis by
precession. It is this movement that produces later and later times
for the beginning of each season and the changing positions of the
stars and planets along the ecliptic. He calculated the value for
precession to be between 45 and 46 arc seconds per year, which is
close to the current accepted value of 50.26 arcsec per year.
Hipparchus had been remarkably close. This discovery is one of his
best achievements, and keeps him among the best ever astronomers that
the world ever produced.
d) He discovered the simple geometric schemes that
represent the motions of the Sun and the Moon. The motions of the
planets he knew were based on the sun-centred or heliocentric system.
He could not improve or drastically change the mathematics to the
meet true positions of the planets. The representation of the orbits
of the planets by the heliocentric system was still impossible to
reconcile, especially for the orbit of Mars that was out by more than
1° than the theory predicted. The only advantage with the
heliocentric system was that it was much simpler in structure. As the
results were just as inaccurate as the geocentric system or
earth-centred universe, proving which theory was correct was
difficult.
e) Hipparchus discovered the exact period of the
Moon’s orbit around the Earth to be 29
days 12 hr 44 min 02.5 sec. This value is remarkably close, only
differing too short by a tiny one second! From this result he could
calculate a particular lunar eclipse to an accuracy of about one hour
or for a solar eclipse to about 4½ hours. This result
reflects the painstaking accuracy that he placed in his observations
and the rigours in the mathematics.
Unfortunately for all his genius, his contemporaries took little
notice, as the size of the then known universe seemed just too
incomprehensibly large to be true. This caused him some personal
ridicule from other natural philosophers at the time, and the
results of his great works were essentially rebuked. The discoveries
of the precession of the equinoxes and his star catalogue will always
remain great contributions towards the development of astronomy.
Today, Ptolemy is not perceived as the most important of the
astronomers from antiquity — yet he has certainly gained the
best notoriety. [3] His major works that have been passed down to us
in their complete form, unlike his contemporaries in which we have
only fragments or from here-say from other writers. The major work
produced by Ptolemy was “Megalle
Syntaxis tes Astronomias” meaning
“The Great Astronomical
System” that simply is called the
“Syntaxis”, in which he gives the chronological
history of the Greek astronomers in the five centuries before his
time. Syntaxis come down to us from the Arabs, under the title the
Algamest or “Kitab al Magisti”. From this Arabic form, it became the major
textbook through the middle ages on the instruction of astronomy.
This book describes Ptolemy’s own
geocentric theory of the planets and was used for nearly 1 350 years
until the time of Copernicus. His theory has been thought to be an
adoption of the works of many others. We think his belief in the
geocentric theory to be based on the writings of Plato (c.420 B.C
− 340 B.C). Plato held the belief, similar to Pythagoras, that
the entire Heavens were based on the harmony, symmetry and the
exactitude of mathematics. To achieve this perfection, the gods
intentions were to have all things spherical. All spheres they
argued, were the most perfect figures of all. Hence, the shape of
Earth and the orbits of the planets had to be also to be based on the
sphere. Assuming the Earth itself was the centre of gravitational
force, all bodies including the planets must always yield to its
power. This leads to the conclusion that the Earth is the centre of
the Universe.
Plato’s logic tempted Ptolemy into a
true belief in the geocentric universe. Having access to the writings
of the most notable of astronomers from the famous Alexandrian
Library, each concluding that the heliocentric or sun-centred
universe was more likely correct. Yet Ptolemy still dismissed it. If
Ptolemaic system was to work, the geocentric form of circles for the
planets orbits must be suitably adapted. This meant that the
retrograde motions of the planets, for example, needed to be
explained. Ptolemy introduced idea of geocentric epicycles. The
planets orbited in circular orbits, in which smaller circular orbits,
called epicycles, orbited within the main system. The method
kept all orbits circular but was obviously very clumsy and
complicated.
Ptolemy’s book also contains a star
catalogue that was taken almost in its entirety from the Hipparchus
catalogue. Ptolemy had added his own observations, with most of the
positions of Hipparchus changed in epoch due to the effects of the
precession of the equinoxes. We know he copied most of this work, as
many mistakes made by Hipparchus were directly translates as
Ptolemy’s. This catalogue is still in
use today, being the basis of an historical record of stellar
positions.
Al-Sufi (903-986 AD) was employed as court astronomer and
teacher of astronomy to Prince Adhad al Daulet, who eventually ruled
all of Persia. He made observations, and produced a catalogue of
1,018 stars that included star magnitudes, colours and positions,
named the “Book of the Fixed
Stars”. We luckily have this book
in its entire form, and numerous fragments of his other publications.
This book was an update but also based on
Ptolemy’s
“Megale
Syntaxis”. Inthis book he revised all
of star positions of Ptolemy. Each part, was elaborately illustrated
with beautiful drawings of the constellation figures. From his
latitude, in today’s southern Iraq, he
observed many southern stars, such as Canopus and the star cluster
around the star Omicron (ο.)
Velorum. Such observations of stellar positions did not seriously
again occur until the 15th Century.
Later Ulugh Beg (1394-1449AD), who was born in Sulaniyya in
Central Asia in Persia on the 22nd March 1394, improved these
observations. By the age of fifteen, he had become the ruler of
Samarkand, succeeded the throne of Persia in 1447, where his son
murdered him on the 27th October 1449. He did, however, built the
largest non-telescopic observatory in the eastern world.
One of the first systematic measures of the positions of the stars
and planets was begun by Tycho. [4] Tycho persuaded King Frederick II
of Denmark to allocate monies for an observatory. The construction
was vast and elaborate and was appropriately named Uraniborg (Castle
of the Heavens). This observatory later provided the important data
that Kepler used to calculate the planetary orbits. One of the first
observational uses of the Observatory was positioning the bright
comet of 1577. Tycho noted that it varied in its velocity, which was
hard to explain, but it also did this rather erratically. Obviously,
the comet had to pass through the theory of the crystalline spheres,
and this observation could only conclude that they did not exist.
Tycho also noted the change in the apparent lunar positions from
different locations throughout Europe, later called parallax,
and showed it could be used to figure out the lunar distance. Using
all these postulates, he correctly concluded that the comet was
actually several times more distant than the Moon.
Although not mathematically trained, his observations were of the
highest precision and accuracy. He discovered, for example, the
length of the year to an accuracy of less than a second. This single
advanced significantly helped to the adoption of the Gregorian
calendar in November 1582. He also contributed improvements in both
measurement and design, and manufactured various instruments, like
the astrolabes, quadrants and equants. [5] He was first to discover
refraction of light through the Earth’s
atmosphere.
This showed that the true position of the star would be actually
lower than its apparent position in the sky, especially when near to
the horizon. He worked out how to fix this anomaly, which is
determined by knowing the true height or altitude of the star above
the horizon.
Kepler later used the use of these positions, and subsequently
Newton, to find the position of the planets. Their contributions were
used to determine the laws of planetary motion, and the prediction of
their apparent positions in the sky. Their stories are well
documented, by the reliability of those places relied heavily of the
known positions of the fixed background stars. It was noted that the
positions, when established, were not as fixed as once presumed. This
was primarily caused by the proper motions of stars that were
constantly changing in their relative positions. We established that
the goals of astrometry could now be extended. Since the accuracy of
the instruments and the mathematical reductions were understood, then
the data could give knowledge of either;
1) Proper Motions of the stars in the solar neighbourhood
2) Nature of the Milky Way
3) Stellar Distances
Between the 1700s and the early 1800s these goals were slowly
obtained. Naturally, other practical uses were also found and the
observers promoted these with vigour at the time. Common sense told
that the pure research into the stellar positions would not be easily
funded unless there was a practical use. The Western world at this
time expanded. The discovery voyages, for example, both Christopher
Columbus and Ferdinand Magellan showed that the Earth was not only
spherical, but had economic and material viability, especially in the
colonisation of the New World. The journeys of these explorers were
fraught with danger, especially regarding the navigation of the
oceans. It is obvious navigation of the oceans, having knowledge
celestial objects was important so they could be used for position
the observer on the Earth. In importance the Sun and the Moon became
the tools for navigation, and began to establish the process known as
dead reckoning. The positioning at the time of the Portuguese in the
1650s (like Magellan) was crude. A sailor could establish the
latitude of his ship to about fifty kilometres, but had no
means of finding the position in longitude. We did not make the first
longitude positioning until 1767, and this was based on knowing the
time accurately by using a ship’s
chronometer. [6] By the analysis of the position of the Sun and Moon
against the background stars, the nautical tables and instruments
were vastly improved. Eventually this lead to the rapid expansion by
fleets of ships exploring all the oceans of the world, like the
voyages of Captain Cook, and in the case of Australia, the discovery
and eventual establishment of the mainland colonies. Production
of these positions lead to the publication of the annular publication
of the Nautical Almanac, that started in 1767.
Later in the 1750s onwards, these positions could be also used for
surveying purposes. These established the rights of ownership of
land, but also a means of determining of property boundaries. (This
also leads to the rights of government to tax land owners, based
accurately on the amount of property that the owners held in their
possession.)
Together astrometry held sway with all governments, so they funded
them, but only meagrely at first. This offshoot meant that
astronomers held some practical advantage, and in turn, provided
astronomers with the means of pursuing the true nature of the
Universe.
More Precise Astronomical Measuring Instruments
The Heliometer
Fraunhofer in the 1820s developed another angular measurement
device called a heliometer. Initially the telescope was
developed to measure the diameter of the Sun to deduce the true
eccentricity orbit of the Earth. This was later adopted to be used to
observe the stars. The heliometer comprises the split objective,
which could be manipulated to merge the solar disk, or two separated
stars some distance apart. Mounted on an equatorial mount, apparent
separations became true measured separations. This instrument
measured the first proper motions and parallaxes.
By 1830, 61 Cygni, or well named
Bessel’s Star, given after
Bessel and Groombridge found the very large proper motion of 7.07
arcsec per annum. This was followed in 1834, the trigonometric
parallax was found, which needed small corrections as the method was
improved, as 0.33 arcsec. (330 mas.), indicating 61 Cygni was one of
the nearest stars. All these devices were typically used to determine
the planetary positions, by they were used also in determining star
places in the heavens.
The Transit Telescope
The transit telescope is an instrument in a long series of
improvement in designed. In the days of its use it was also known as
the universal instrument. As a group that started from the quadrants
and meridian circles of ancient times — with the telescope
attached instead of looking alone a fixed straight path. The transit
telescope was established as a primary instrument somewhere between
1760 and 1780.
Its use is based on the determination of the time when some star
crosses the meridian at the place of observation. When accurately
determined, of which the transit telescope is the most famous, this
place marks the local sidereal time, and hence, the true apparent
time for that longitude. The precise graduated circles also give the
star altitude on the meridian from the zenith or northern and
southern horizon — simply based on these two values, thus
obtaining the precise longitude of the location. We measure longitude
from the position of the transit telescope at Greenwich Observatory
in England, now parts of the National Maritime Museum. This
instrument marks the internationally agreed zero longitude of the
world.
When we have proved the position of the transit, this fixed
position can be used to measure the accurate position of the stars
then, and over time, the motions of the stars in question. Although
explaining the device of a transit telescope, explaining how we
obtain the results is hardly simple. The regimes of mathematical
calculations and of the errors are too broad based for a simple
discussion in this paper. Understanding the mechanical complexities
of the instrument and the history of the mathematical computations is
possibly more useful. The nature of the mechanics problems of the
transit telescope are complex, but the following quotation summarises
this adequately;
“We cannot falter ourselves that the
instruments, even if still perfected, will allow us to advance
farther and to increase accuracy beyond one second of arc. It is
quite possible that Bradley has therein the limits of our
knowledge.”
Jean Sylvan Bailly (1782)
The precision of mechanical devices at the time of the
pre-Industrial Revolution was inadequate for the highly accurate
needs of astrometry. They faced two problems; the accuracy of screw
threads and the high precision needed in milling graduated circles.
For example; 1.0 arcsec (arc seconds), represents the required
accuracy for two-metre meridian circles to one hundredth of one
millimetre.
The instrument makers of the company of J. Repsold in 1802, who
made first accurate circles that were suitable for astrometry and
then by Reichenbach in Munich in 1804. The first meridian circle of
note was by Reichrenbach’s, and was
used by Bessel in Prussia. Each of these circles was initially used
for geodetic work, which they later adopted for improvements in
sextants in use for navigation. Similarly, trigonometry developed the
mathematics in obtaining accurate star place, latitude, longitude and
the ability of handling astronomical corrections. The oldest methods
for accurate transit telescopes date to America in 1844.
Instead of looking at a star and listening to the ticks of a
clock, observers registered the moment of transit across the
cross-hairs of the micrometer by trapping the signal key set to a
chronograph, with the clock registering the time in seconds. Using
this method, accidental errors were reduced from 0.5 sec to 0.06 sec
in time. Multiple measures across the graticule further improved the
results using several parallel wires, and reduced the systematic
errors.
The mathematically talented German astronomer Bessel in the
1810s developed the new astronomical field of precision astrometry by
improving instrument designs and developed some mathematical methods
to improve accuracy. Due to this work early in his career, he started
to reduce the vast backlog of data produced in the years before. I.e.
Mostly Bradley&38217;s observations, but also some others. Bessel
then joined with the English astronomer Bradley, analysing his
observation because of Bradley’s
precise measurements with their known errors. It was from these
accurate analyses that both Bessel and Bradley discovered the sources
of errors, like nutation (about 8 arcsec), the aberration of
starlight (about 20 arcsec) and refraction. The culmination of these
results lead to the first set of astronomical constants in the
“Fundamenta
Astronomiae” in 1818.
By 1820, he had installed a new meridian circle, and again later
on 1841 an instrument by Repsold. This lead Bessel to personally
made 60,000 transits. These all lead to final measuring the distances
of the stars, by stellar parallaxes. Unfortunately, many problems
still existed then with transit instruments in measuring the
parallaxes by either micrometry or timings. The problem — the
angles were too small. However, by the 1850s, they reduced the errors
to make parallaxes a bit more practical. To show the general problem,
each Transit Instrument has to have enough corrections applied to the
mechanics of the system. Bessel uses to quotation quite often;
“Every instrument in
this way is made twice, once in the workshop by the artisan, in brass
and steel, and then again by the astronomer on paper, by means of the
necessary corrections which he derives by his
investigations.”
Errors were typically between 1/1000th and 1/100th millimetre for
the measurement, combined with atmospheric refraction, temperatures,
pressure, time of day, etc. Next was the need for corrections for
precession, nutation and light aberration. The reductions by the
1850s fell to 0.01 arcsec in declination, and 0.001 seconds in Right
Ascension. In 1848, George Airy, helped by the engineer Charles May,
built the first modern transit circle, now called a transit
telescope. Its first use did not occur until 1851. Three years
later, transits were also first timed electronically by Airy [7],
when he had first reduced most of the planetary and stellar transit
data when coming into office as Astronomer Royal in 1835. He then
held this position until 1881. At the time, the English had mostly
lagged behind most of these technological aspects, but British pride
presented by the King was beginning its ascendency. Under
enthusiastic Airy, and due to
Greenwich’s unbroken series of
observations, Greenwich became the new centre of world affairs for
navigation by sea, astrometry and geodesy. Greenwich under him also
grew during this time, both nationally and internationally.
All meridian work developed in a set up positions for so-called
fundamental stars. Bessel set up the 3,436 stars. This was later
increased by “zone
work” for all the stars, which
developed (as a natural progression) into the Astrographic Catalogue
of stars between the 1870s to 1880s.
This was later completed in the August 1958, concluding after
further correction in 1971.8. Further information was then deemed
necessary by Bessel and Lalande — whose drive and motivation
was later extended by Airy, because they all knew that the proper
motions were not very well known. They also knew if such data were to
be gathered it would take beyond their own lives. Bessel estimated
that a hundred years must elapse before we would reliably obtain such
information. (This partly concluded in early 1900s to 1930s)
The problems of the southern sky became paramount, and the legacy
of southern astrometry beginning late compared with the northern
stars, lead to poor knowledge of stellar motions even into the 1960s.
The first accurate portioning and parallax culminated in the southern
hemisphere with the SAO (Smithsonian Astrophysical Observatory
Catalogue). Here the precision of this data is slightly poorer
compared with their northern cousins. Recently, the Hipparchus
satellite improved the data. Released in August 1996, the parallaxes
for some 100,000 stars were obtained, and we changed the role for
transit telescopes forever.
Short History of the Astrometry in New South Wales
William Dawes made first astrometry in March 1788. This was mainly
to set local time and standardise the longitude and latitude of
Sydney. His second goal was to observe the positions of the return of
a periodic comet, which never came about. Next Parramatta Observatory
was established in 1821. (34 years after the arrival of the First
Fleet.) It began observations in the next year, under the
directorship of Sir Thomas Brisbane, and the two observers
Rümker and James Dunlop. [9] Brisbane defrayed the original cost
instruments and the wages of two observers himself.
Quickly, Parramatta Observatory established an extensive observing
programme. The primary undertaking was a catalogue of star positions
in the southern skies using a mural circle, a meridian telescope, and
then a small 3¼-inch transit. Within three years, in 1825, the
places of 7 385 stars were determined, the basis of which became
known as the Parramatta Catalogue of Stars. The Royal Astronomical
Society rewarded the efforts for this to Brisbane in 1828 with the
prodigious Gold Medal. [10]
In the years after about 1836, Parramatta Observatory fell into
disuse [11], so astrometry progressed sporadically — mainly to
the determination the local time by the measures of the sidereal
time. Stellar positioning only re-emerged in the mid-1850s. The
meridian telescope of the old Parramatta observatory was sent to
England for repairs in early 1857, and was returned in late in
1858.
Reverend William Scott had arrived in 1856. After being nominated
by Airy himself, who was highly he was interested and motivated by
astrometry, he began almost immediately when Sydney Observatory was
completed — started his work on 5th December 1868. Scott
particularly observed stars culminating near the zenith, and towards
the south celestial pole. His work was meant to be extended
(according to Airy) at the Cape of Good Hope and the results climaxed
in two published volumes in 1859 and 1862.
H.C. Russell continued this programme and work, who was primarily
enlisted because of recent graduation from the University of Sydney
as dux of mathematics and physics. The Transit Telescope at Sydney
Observatory, replaced the relocated the Edward Troughton
3¼-inch Transit Telescope, from Parramatta Observatory, which
was made in 1820. The transit telescope, is the 6-inch Transit Circle
Troughton and Simms instrument that was made in 1876, as order and
organised on the behalf of the NSW Government, by the English
Astronomer Royal, Sir George Airy. The manufacture was concluded in
March 1876, so it is now more than 120 years old.
The first observations started in 1877, but because of this was in
the middle of the two transits of Venus (1874 and 1882) and
Russell’s other undertakings, Russell
devoted a small percentage of time to the extensive observation
programme. However, Russell did carry out positional measures of the
Tebbutt’s Great Comet of 1881. In 1878,
the Observatory was also responsible for the surveying.
The Government decided to handed over this work to the New South
Wales Lands Department, whom from then on produced the detailed
trigonometric survey of NSW.
This year also marked the deviation of non-astronomical ventures
by Russell, required by the elected Colonial government. A nominated
Board became then responsible for the Observatory running and
requirements of capital works and funding projects. (Probably under
the direct influence Russell himself.) This broke away from the
directions of single-minded Airy. From then on, transit observations
became very sporadic in the next few decades.
The introduction of the Astrographic Catalogue replaced
many of the observations that the transit telescope was supposed to
fill. However, the central positions of the plates were checked from
time to time, and in some ways, both the transit and the Astrographic
Camera were really used in tandem. In the 1920s, W.E. Cooke initiated
the last true positioning of stars using the transit in the survey of
1,068 stars within the Astrographic Catalogue. This was completed
successful but was greatly hindered by the encroaching light
pollution from the city of central Sydney. It is fascinating to see
that astrometry has remained very prominent throughout the history of
Sydney Observatory. This is despite the worldwide direction of the
astronomical community moving towards the sub-science of astronomy;
namely, astrophysics.
Aspects of the Sydney Transit Telescope
Usual the first established areas of transit telescopes are the
azimuth piers, that give the telescope the north-south alignment.
This would have been field tested with a small transit telescope or
theodolite.
The first is made using two wooden pegs some 150 to 200 metres
away, and secondly using an alignment telescope. Originally, it would
have been marked by the temporary stone pier, and some ten of metres
away to the north and south of the position of the transit
instrument. [12] The important 5.0cm (2-inch) alignment refractor on
the north side of the transit room was placed when not in use in a
wooden box. [13] A hole in the wall aperture is for this instrument
alignment. It is used for checking the actual north-south line, that
must be occasionally checked, and is place in case of misalignment
either by accident, sagging of land or earthquakes. This also allows
the mechanism to be aligned east-west by another alignment telescope
or by a mirrored arrangement. Normally this alignment is through the
centre of the altitude-azimuth axis and also passes through the
centre of the transit telescope.
The telescope itself is placed between two fixed piers, supporting
the graduated meridian circles, and is more properly called the
vertical circle. Towers towards the west an east hold the meridian
circles, are made so they can be independently aligned. Each tower
has a set of alignment screws, that is adjustable outside their
respective cabinets. The vertical circle, and other mechanical
information is then extracted by the various eyepieces around these
adjustments. Initially, these were illuminated by gas light, but were
replaced around 1910 by incandescent lights using electricity. The
observer placed the telescope alignment to the declination of the
star in question.
Next the observer is placed under the telescope and waits until
the star in question entered the field. A single transit is never
taken, as multiple measurements prove to be much better to decrease
the errors. Originally, stars are measured by the ear/eye method, but
this was soon replaced by the electronic signal sent to the drum
chronograph. The chronograph produced regular ticks on the graph
paper in the drum, except for the 59th second. Later, some results on
other similar instruments actually printed the time. Observers simple
to pushes the button when the star was occultated by the micrometer
wire, that placed a permanent mark on the paper that was wrapped
around the recording drum.
Results, could then be calculated later at a time more convenient
the astronomer, especially if the position of the star was required.
Otherwise a brief calculation, could be used to adjust clocks and
other chronometers to give the correct sidereal or local time.
Transit telescopes were eventually replaced by the portable
theodolite (1908), with the last Airy Transit of this generation was
made in 1888.
Final Summary
I hope that this general paper may have stirred some interest when
we look at the transit telescope through the eyes of the annals in
history. The transit telescope at Sydney Observatory is an instrument
that has become antiquated for modern astronomy. Although they have
superseded its role thrice since its working life over its one
hundred and twenty-year history, it remains from a vital reminder in
the development of astronomy in Australia. It is unfortunate that the
many visitors to this establishment will quickly walk by the
telescope, giving it only a short glance. Perhaps it is the
enthusiasm of getting up to the domes and peering at the night sky,
but it is more likely the disrespect our modern times have placed on
all things that are old. To me, the design, the mechanics of the
mount and the amount of thought required for its use is the
absolutely amazing. Unlike most of the modern instruments of today at
least I can touch it. (Still, don’t
tell the staff of this Observatory I have done so!)
Reference Notes
#1 : Hipparchus, or more correctly Hipparchos,
was born in Nicaean Bithynia. We have very little information on his
life or any of his personal qualities. We know that he was not a
philosopher, but it was his mathematical techniques and analysis that
gave him fame. Unfortunately, all books written by him, save one of
his unimportant works, have been destroyed. Details of Hipparchus
(and Eratosthenes) are given in Pliny’s
“Historia
Naturalis” (Natural History). Pliny
(23 AD.−79 AD.) describes him as a major contributor to science
and summarises his achievements.
#2 : Some of Hipparchus mistakes, for instance
were duplicated by Ptolemy.
#3 : Claudius Ptolemaeus Pelusiniensis or
Ptolemy (c.90 - c.141-151 AD) was born, it
is suggested, in Ptolemaic Hermii on the banks of the Nile. His date
of birth and death are uncertain, however we know he was a geographer
and an astronomer, living and working in Alexandria. In this city, he
is believed to set-up an observatory on the high roof of a temple.
Ptolemy is thought to have died at the age of seventy-six
years old, in either 141 or 151 A.D.
#4 : Tycho was born into nobility in 1546, in
Kudstrup, South Sweden under the then Danish Government. In his later
life his most distinguishing feature was that he had a gold nose,
that was lost in a sword duel. His personality was said to be
abrasive, to the point of almost being rude, and with the aristocracy
he was considered a drunkard. He became interested in astronomy at a
young age of thirteen or fourteen, until his
observational interest increased by the appearance in the northern
constellation of Cassiopeia with a “new
star” in November 1572. This star
continued to increase in brightness over several weeks to become as
bright as Venus. It remained in view for a few months before it fell
again fell below naked-eye visibility. This amazing star was later
classified as an exploding star or supernova. Tycho did not
have any significant academic background, and as such, was was not
talented enough to properly analyse his data. Yet when it came to
observation, he was dedicated and exact, especially with his
non-telescopic equipment. When his patron, King Frederick II died,
Tycho left for Germany in 1597. Eventually he travelled to Prague, at
the request of the emperor, to become the Assistant Astronomer.
Subsequently he was introduced to Johannes Kepler who was also
employed under King Frederick II. Kepler saw, and gratefully accepted
Tycho’s tables and observations, that
continued other important developments with planetary motion. He died
in Bentatky, Prague on the 24th October, 1601 at the age of
fifty-six, possibly from excessive drinking during his later
life.
#5 : These were the ancient instruments to
measure stellar or planetary objects as they travelled across the
celestial sphere.
#6 : Anson in 1741 knew this problem directly.
He had underestimated, guessing wrongly of his longitude. Distance at
sea was typically made by travelling along a parallel of latitude and
roughly estimating the distance travel by the speed of the ship. His
crew, and nearly himself, suffered from loss of live by scurvy, and
in his case, loss of life in a shipwreck.
#7. : This, like the instrument at Sydney
Observatory, is more correctly called an Airy Transit Instrument.
#8 : Sydney contribution to the Astrographic
Catalogue finished in 1964. Sydney took over the Melbourne
Observatory portion of the catalogue in 1944 when Melbourne
Observatory was closed. The final publication of the Astrographic
volume No.52 concluded the work in 1971. The entire work measured
over one million stars in the declinations from −36° to
the south celestial pole.
#9 : The actual transit observations are
relatively simple to undertake, (a common fault with most of the
astronomers at the time who saw them as
“cannon
fodder”, and therefore paid for their
assistance a pittance. (except Flamsteed between 1660 to 1680.)
However, the reductions for the positions were very difficult, so the
astronomer typically took all the credit. The mathematics, once the
procedure was organised, could be done by computers; operators who
did the tedious calculations by hand.
#10: James Dunlop in 1828 was similarly
awarded the Gold Medal for his observations and catalogue of 621
nebulae and clusters and his 253 double stars. Most of these were
discovered during the period when the observations were being made
for the Parramatta Catalogue. It seems that the majority of these
transit observations were actually made by both Dunlop and
Rümker. Later during 1858, Rümker was to be recognised by
the Royal Astronomical Society for his contributions in many if the
observation made at Parramatta.
#11: Today, the only visible existence of
Parramatta Observatory is the transit piers, located near the
south-eastern entrance of Parramatta Park, some three hundred
metres from the building of the old Colonial Government House.
#11: The first southern alignment pier, a
two-metre stone piece has been physically removed out of the ground
(presumably during the observatory’s
renovations after 1983?)
#13: This was removed in May, 1987 and placed
into storage.
Last Update : 10th August 2012
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(2012)
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