International Year Of Astronomy

International Year of Astronomy400 Years of Astronomical

Telescope

T V Venkateswaran

Galileo did not invent telescopeNor 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 Telescopeis 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.

Those with nearsighted had problem of seeing things at far. They needed concave lenses. Only after 15 century concave lenses were fabricated. Those with farsighted had

problems of seeing things near. They needed convex lenses. Initially convex lenses were made.

Discovery of lenses

•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. Lippershey 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 telescopeGalileo 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 advocates its military potential as a spy glass.

His initial version only magnified 8x but was soon refined to the 20x magnification he used for his. It had a convex objective lens and a concave eyepiece in a long tube.

Galileo’s revolution..

• Mountains on the moon • Jupiter’s satellite• Milky way• Gibbous phase of Venus

Scientific Method to understand nature deeper…

August 25, 1609

January 19, 1610 stellar occultation

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.

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 drawing of the phases of Venus and modern photo-

mosaic

Copernicus

Ptolemy

From observing the phases of Venus he could conclude heliocentric theory

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.

Galileo then turned his attention to most numerous objects in the night sky- stars. 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.

Through naked eye Through telescope

Galileo Galilei published Sidereus Nuncius, or the 'Starry Messenger ' in 1610. In it he provided a lively and accessible account of his telescopic observations. This revolutionized the astronomy as well as sciences.

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. Thus there is a two distinct

areas- Terrestrial- with all the imperfections; Celestial with no blemish and all perfect. Aristotle believed that the laws governing the motion of the heavens were a different set of laws than those that governed motion on the earth.

Contrary to reality, Aristotle claimed that heavier ball will fall first !

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.

That is there was epistemic rupture between 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 Ragu -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, his imprisonment 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 was kept working.

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.