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International Year of Astronomy
400 Years of Astronomical Telescope
T V Venkateswaran
VIGYAN PRASAR,
New Delhi
Galileo did not invent telescope
Nor was he the first to use it for
astronomy!
The telescope was unveiled
in the Holland.
In October 1608 patent
application was filed by
Hans Lipperhey
First known use for astronomical
purpose
We know that Thomas
Harriot observed the Moon
with a six-powered
instrument early in August
1609, months before Galileo
Significance of Galileo
• He did not just ‘use’ the
telescope- he fabricated
his own …
• He did not just ‘see’ the
heavens, but applied
scientific method to
interpret what he saw…
The actual term "telescope" was coined on April 14, 1611 by
Prince Frederick Cesi at a reception where Galileo was
demonstrating one of his instruments.
Development
of Telescope
is linked to
that of
spectacles
With
age,
the
eye
progressively loses its power
to accommodate, that is to
change its focus from
faraway objects to nearby
ones.
This
condition,
becomes noticeable for
most people in their forties,
when they can no longer
focus on letters/ books held
at a comfortable distance
from the eye. Magnifying
glasses became common in
the thirteenth century for
reading
Ancient Egyptian hieroglyphs
dated back to the 8th century
BC depict "simple glass
meniscal lenses".
A Tamil poet, Kapilar, of
Sangam era (about 1 C BCE)
states that a dewdrop on a
grass could make the image
as large as a Palmyra tree,
thus
indicating
an
understanding
of
the
principles of magnification.
The earliest evidence of
"a magnifying device, a
convex lens forming a
magnified image," dates
back the Book of Optics
published by Alhazen
(Ibn al-Haitham) in 1021.
Its translation into Latin
in the 12th century was
instrumental to the
invention of eyeglasses
in 13th century Italy.
At first the lenses (lens means lentil in Latin, so called
because of the shape of the pieces of glass used) for
the eyeglasses were made by cutting discs out of
balls of blown glass. These were called as ‘Reading
stones’.
Venetian glass blowers,
who had learned how to
produce glass for reading
stones, later constructed
lenses that could be held
in a frame in front of the
eye instead of directly on
the reading material. It
was intended for use by
one eye
Around 1284 in Italy,
Salvino D'Armate is
credited with inventing the
first wearable eye glasses.
Spectacles making and
usage spread rapidly with
the spread of literacy.
The earliest pictorial
evidence for the use of
eyeglasses, however, is
Tomaso da Modena's
1352 portrait of the
cardinal Hugh de
Provence reading in a
scriptorium.
Discovery of lenses
Those with farsighted had
problems of seeing things near.
They needed convex lenses.
Initially convex lenses were
made.
Those with nearsighted had
problem of seeing things at far.
They needed concave lenses.
Only after 15 century concave
lenses were fabricated.
•In the late 15th century the spectacle-makers of
Nuremberg began however to cut the discs out of plates
of flat glass and then grind one of the surfaces to either a
concave or a convex shape.
•Through this procedure, lenses with more accurate
spherical curvature could be produced.
•It was the spread of this perfecting technique that made
the invention of the telescope possible.
Lipperhey was one such spectacle maker in Holland. One
story behind the creation of the telescope states that two
children were playing with lenses in his shop. The children
discovered that images were clearer when seen through
two lenses, one in front of the other. Lipperhey was
inspired by this and created a device very similar to today's
telescope. Of course it was called ‘looker’ by him and not
telescope.
Lipperhey
Lipperhey applied for patent
in 1608 to the government.
He was unable to get a
patent, however, because
his invention was deemed
too easy to reproduce. He
however produced number
of opera glasses for viewing
opera in the theatre.
Soon telescope spread throughout Europe.
English scientist Harriot bought one from Dutch
and used it to observe moon
Galileo’s telescope
Galileo found out about this
invention in the early 1609
and immediately set about
improving it.
•He realized that the magnification was proportional to
the ratio of the power of the concave (eyepiece) lens to
the convex (more distant) lens.
•In other words he needed a weak convex lens and a
strong concave lens.
• Opticians only made glasses in a narrow range of
strengths, and three or so was the best magnification
available with off the shelf lenses.
Galileo learned to grind his own lenses, and by August
1609, he had achieved about eight-fold linear
magnification. He demonstrated his new invention to
a gathering of officials on August 1609. Initially Galileo
advocated its military potential as a spy glass.
Galilean Telescope
Galileo used a long focal length
objective and a short focal
length eye piece. If the focal
length of the objective is Fo and
the focal length of the eyelens is
-Fe, the distance between them
must be Fo - Fe, and the power
(angular magnification) is Fo/Fe.
Image is upright.
"When there are no glasses in the tube, the rays proceed to the object FG along the
straight lines ECF and EDG, but with the glasses put in they proceed along the refracted
lines ECH and EDI. They are indeed squeezed together and where before, free, they
were directed to the object FG, now they only grasp the part HI"
Galileo’s revolution..
His initial version 8x but was
soon refined to the 20x
• Mountains on the
moon
• Jupiter’s satellite
• Milky way
• Gibbous phase of
Venus
Galileo could see stellar
occultation, mountains on
moon, calculate the height
of the moon and so on. At
one stroke he could
change the way moon
looked.
January 19, 1610
stellar occultation
He observe that some parts
of the moon were illuminated
well before its surroundings
by the sunlight. We know that
mountain tops are illuminated
at the dawn well before the
valleys. He built a convincing
case for the reality of the
mountains by sketching the
appearance of parts of the
Moon’s surface at different
times of the month, that is,
under different angles of
lighting. Obviously this
caused uproar. The orthodox
were enraged, how can
Galileo claim that moon, an
celestial body to be
‘imperfect’
Galileo’s next major discovery began with
his observation on January 7, 1610, of
what he took to be a rather odd set of
three small fixed stars near Jupiter. These
‘stars’ were invisible to the naked eye.
Observations over successive night
revealed that actually four star-like
objects in a line with it. The objects
moved from night to night, sometimes
disappearing behind or in front of the
planet. Galileo correctly inferred that
these objects were moons of Jupiter and
orbited it just as our Moon orbits Earth.
By the 15th January 1610 had realized
that he was looking at moons of Jupiter.
Through naked eye
Through telescope
Galileo then turned his attention to most numerous objects in the night skystars. Rather to his disappointment the stars showed no features- they were still
point source, even through a telescope the stars still appeared as points of light.
Galileo suggested that this was due to their immense distance from Earth. On
turning his telescope to the band of the Milky Way Galileo saw it resolved into
thousands of hitherto unseen stars. In like manner when ex explored the region
of Pleiades, he found stars that were unseen to naked eye. His exploration of
the Orion nebula also revealed unseen stars.
Galileo Galilei published Sidereus
Nuncius, or the 'Starry Messenger ' in
March 1610. In it he provided a lively
and accessible account of his
telescopic observations. This
revolutionized the astronomy as well
as sciences.
Latter…
Copernicus
Galileo’s drawing of the phases of Venus
and modern photo-mosaic
Ptolemy
From observing the phases of Venus he could conclude heliocentric
theory
His telescopic observation of
Saturn resulted in total
shock. Initially Saturn
appeared to have ears, and
latter some kind of
appendage. Galileo could
not make sense of it.
Few decades latter,
Huygens using a better
telescope resolved it as ring
around Saturn.
In any case Galileo’s
observation showed that
stellar objects need not be
perfect sphere.
Aristotle believed that a
stone fell to the ground
because the stone and
the ground were similar
in substance (in terms of
the 4 basic elements,
they
were
mostly
"earth"). Likewise, smoke
rose away from the Earth
because in terms of the 4
basic elements it was
primarily air (and some
fire), and therefore the
smoke wished to be
closer to air. Likewise
heavenly bodies were
perfect
without
any
blemish and moved in
uniform circular motion.
Contrary to reality, Aristotle
claimed that heavier ball will fall
first !
To the first sight, for the
Earth-bound observers,
while rain, wind and
erosion kept changing
the features of the
Earth’s terrain, hardly
anything changed in the
heavens. Day after day
the sun rose in the east;
month after month the
moon waxed and waned
in the same manner; year
after year the sun
appeared to go around
the Earth, and all the
while stars appeared to
be fixed and immobile.
Aristotle thus made a clear distinction between
the heavenly (celestial) and terrestrial
(sublunar)
realms,
the
former
being
unchanging, perfect etc and the latter being
changeable, imperfect and so on. Hence it was
assumed that laws that were applicable to one
realm would not apply to another and this
cosmic divide lasted for centuries. This was
held by the orthodoxy as an immutable dogmato be taken as faith.
Seeds of doubt
Galileo had earlier observed a
‘new star’ in October 10, 1604.
Today we know it as supernovaexplosion of a star. It was first
observed by Kepler on Oct 9,
1604
in
the
constellation
Ophiuchus and hence called
Kepler’s Nova.
Galileo went a step further. He
made parallax measurements
and found it to be beyond Moon,
in the starry realm. Therefore he
had his first inkling that
something was amiss in the
Aristotelian idea of unchanging
cosmos.
Galileo's
extensive
telescopic
observations of the heavens made
it more and more plausible that
they were not made from a perfect,
unchanging
substance.
In
particular, Galileo's observational
confirmation of the Copernican
hypothesis suggested that the
Earth was just another planet, so
maybe it was made from the same
material as the other planets.
It was radical and an epistemic
rupture of celestial and terrestrial.
Same laws of physics applied in
both cases. One set of science is
all that is required to explain
‘heaven and earth’!
Just as Aryabhatta was condemned for his views against the purnaic
myth of Rahu -Ketu, Galileo was punished by the orthodoxy in Europe for
daring to put forth his theories. He was to suffer for many years for
upholding science and sprit of quest against mindless dogma.
In July 1633, he was imprisoned and latter his sentence was converted into
life-long house arrest, because of health reasons. He was not allowed to have
contact with the outside world. Until his death, even at his old age he kept
working.
Down but not Out
Although Galileo was ill and mentally exhausted, he started to write a book
about mechanics, based on his research in Padua. This book, Discorsi, or
Dialogues Concerning Two New Sciences was published by Elzevier in
Leiden, because it could, of course, not be published in Catholic lands. The
book convincingly argued against the Earth centered universe and upheld
the scientific sprit. No wonder the 400th annivesary of Galileo’s use of
telescope is celebrated as International Year of Astronomy.
The major goals of IYA2009 are to:
• Increase scientific awareness.
• Promote widespread access to new
knowledge and observing experiences.
• Empower astronomical communities in
developing countries.
• Support and improve formal and informal
science education.
• Provide a modern image of science and
scientists.
• Facilitate new networks and strengthen
existing ones.
• Improve the gender-balanced
representation of scientists at all levels and
promote greater involvement by
underrepresented minorities in scientific
and engineering careers.
• Facilitate the preservation and protection of
the world's cultural and natural heritage of
dark skies in places such as urban oases,
national parks and astronomical sites.