The
Observations
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With
just a few dim lights, astronomers would have witnessed
a beautiful sky. 15 August 1852 3.45am, looking directly
south towards Wimbledon
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Soon
after the telelscope was completed, Craig was keen to begin
observing evenings. He invited many prominent astronomers
to visit his telescope, including William Parsons, builder
of then the World's largest reflector - having a mirror six
feet in diameter.
We
can imagine what the summer sky would have looked like in
the early hours of a warm autumn morning. The huge constellation
of Cetus the whale would have been stretching across the southern
horizon with Taurus the bull swinging high up over the south
eatern sky. The vista would have been punctuated with a miriad
of stars. With only the small town-lights of Wimbledon glowing
very faintly on the southern skyline, the heavens would have
been a magnificent sight. Added to this, Saturn will have
been shinning brightly with its pale hues towards the south
east.
Perhaps
Craig had been inspired by the Great Exhinition in London
in 1851. Perhaps he had made a visit especially to see what
wonders were inside the Crystal Palace. Ceratinly inside there
were many scientific inventions and aparatus including a wonderful
26-inch refractor. Richard Panek author of "Seeing and
Believing: How the Telescope Opened Our Eyes and Minds to
the Heavens" refers to a specific display,
"In
1848, only a year after the telescope went into operation,
Bond (the observatory's director) and his son George Phillips
Bonds (himself a future director) discovered Hyperion, the
eighth satellite of Saturn. But it was their ongoing interest
in the application of photography to astronomy that perhaps
most distinguished this telescope's early contributions. Their
daguerreotypes of the Moon won a medal at the Great Exhibition
of 1851 at London's Crystal Palace. A few years later, after
the addition of a new clock drive to the telescope, the younger
Bond embarked on an ambitious program of photography based
astrometry (the measurement of the positions, parallaxes,
and proper motions of celestial bodies) and photometry (the
measurement of light)".
The
main purpose of Craig's telescope was to observe both Venus
and Saturn. John Craig believed that he could use the telescope
to confirm the existence of the Crepe Ring discovered inside
the main ring system of Saturn by W. C. and G. P. Bond in
1850. Actually the ring had been observed on several occasions
many years earlier by a number of prominent astronomers.
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In
an extract from the Illustrated London News 16 October 1852
we find, "When news of this reached
England, the Northumberland achromatic, at our Cambridge University,
was brought to bear, by Professor Challis, on the rings of
Saturn, and he failed in discovering the third: so, also,
with the giant reflector of the Earl of Rosse. Hence it became
a matter of intense interest, as to whether there was in reality
a third ring. We are happy now to exhibit an Engraving of
the Ring, as seen in this country. In the Craig Telescope
- engraved and described in the Illustrated London News for
August 28 - this third ring is quite palpable; so that there
can be no longer any doubt as to its existence. The colour
of this ring is a brilliant slate. The great quantity of light
which the telescope at Wandsworth brings to the eye of the
observer from this planet gives, we presume. this bright appearance
to what in instruments of less power is in fact completely
invisible."
There
are references about photographs being acquired through the
telelscope. However, since the instrument was in no way driven,
it was unable to track any celestial object. This would have
limited its photographic capability greatly. The only objects
where exposures were short enough to have foregone a drive
would have been the Moon and the Sun.
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In
paper read at the annual meeting of the British Association
of 1854, it refers to "photographs" that had been
taken through the Craig Telescope, "Dr.
Diamond, who printed the positive of the moon, found the sun
picture, however, rather overdone for transferring. "It
will be necessary, therefore, either to use collodion and
nitrate of silver simply without any or but little sensitive
solution or else pass the sun's rays through some coloured
glass, which will partially retard their energy. A series
of pictures of the spots of the sun, as well as of the general
surface, may then be successfully obtained; and hence it is
not too much to anticipate some accession to our knowledge
of the physical character of both our great luminaries by
means of this gigantic telescope, which Dr. Diamond enables
me to exhibit photographically to the [Astronomy] section."
It
was also a wish of Craig to finally answer the question as
to whether Venus possessed any moons. The debate had been
around for some time and it was hoped that the new telescope
would be able to solve the issue.
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Illusory
Satellite of Venus
by
Montaigne of Limoges in 1761 |
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Venus
lies inside the orbit of the Earth. Through a telescope it
exhibits phases just like our Moon - with some of its surface
not illuminated by the light of the Sun. If it possessed a
moon it too would exhibit phases. The illustration by Montaigne
which he sketched in 1761 shows what appears to a moon of
Venus at various positions in its orbit around Venus. Certainly,
from this drawing it shows that if indeed there was a moon
it appeared the same size as our moon but orbiting considerably
closer!
There
are essentially two ways in which to discover a moon for Venus.
Firstly to observe it directly. This is a little tricky as
Venus always stays close to the Sun in the sky. Great care
would have to be exercised. Potentially, it could mean accidently
looking directly at the Sun leading to imediate blindness!
Secondly, wait for Venus to transit over the Sun's disk. Using
a special solar filter, it would be possible to see any little
moons of Venus as very small black spots moving over on the
Sun's surface. However, these transits are extremely rare
occuring in pairs every 122 years. When Craig built his telescope
in 1852, the next Venus transit would occur in 1876. Unfortunately
the telescope had already been demolished by then.
To
discover a moon would resolve Venus' mass and density; it
would give scientist a better understanding of Venus as a
planet.
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