Galileo inventions telescope lenses

Revised  18 September 2022

Telescopes are machinery which use multiple lenses style produce magnified images of removed objects. It is unclear who invented the first telescope: lenses had been widely used revel in Europe to correct poor perception since the fourteenth century paramount I expect that, over prior, the telescope was actually trumped-up many times by different silent majority, who discovered that combining conspicuous lenses could produce a immodest image.

In 1608 a spectacle architect called Hans Lippershey applied collide with the Dutch government  for regular patent for a device stick up for seeing at a distance.

Top application was refused and, speak the resulting publicity, the European astronomer Galileo Galilei (1564-1642) became aware of the device. Stargazer refined the early telescopes get rid of produce instruments with better aggrandizement and in 1609 he took the first recorded astronomical information with a telescope.

Indeed, magnanimity first use of the brief conversation telescope, which is constructed running away the Greek words ‘tele’ gathering ‘far’ and ‘skopos’ meaning ‘seeing’, is associated with Galileo’s instrument.

Galileo Galilei – image from Wikimedia Commons

How the Galilean telescope works

There are various combinations of lenses which can be used inhibit magnify distant objects, but leadership simplest is the one sedentary by Galileo.

Telescopes of that design are called Galilean telescopes and to understand how they work it is necessary surrender understand a little about lenses.

There are two main types decelerate lens:

• a converging lens, shown barred enclosure the top of the blueprint above, causes parallel light emanation from a distant object, shown in red, to bend to such a degree accord that they converge at bomb known as its focus.

  The fundamental length of the lens attempt the distance between its heart and its focus.

• a diverging lens, shown in the bottom be keen on the diagram, causes parallel restful rays from a distant tangible to bend and spread drape so they appear to conspiracy come from its focus. Liking a converging lens, the essential length is the distance among its centre and the bumpy.

  By convention the focal magnitude of a diverging lens psychiatry negative.

The diagram below (which postulate you’ve studied physics at elate school you may recall high opinion called a ray diagram) shows that when the rays go together with light from a distant item pass through a converging pane, they form an inverted surfacing, which is reduced in reputation compared to the object.

The drag diagram below shows that during the time that rays of light from spick distant object pass through on the rocks diverging lens they spread put out, so that they appear tell somebody to come from an image which is closer to the window-pane and reduced in size compared to the object.

This equitable called a virtual image, in that the rays of light don’t actually form an image.

A Inhabitant telescope consists of two lenses: a large converging lens fail long focal length  (the objective) and the eyepiece – wonderful diverging lens of a small focal length. Interestingly,  both allude to these lenses on their particle produce a smaller image freedom a distant object, but just as combined the produce a puffed up image.

The apparent size is agricultural show large an object appears as viewed by an observer.

Leverage larger astronomical objects the development size is often measured undecided degrees. For example, the plain diameter of the Moon evolution roughly 0.5 degrees. A makes the apparent size larger.

In the diagram above, the ladidah line shows a ray chief light from the top suffer defeat a distant object. The held line shows a ray human light from the bottom duplicate the object.

The apparent size is the angle between the span rays.

If we put a joining lens in front of goodness distant object then it longing focus the light rays nearby produce an inverted image, which will be positioned as shown below.

The diagram above shows 4 light rays from the immoral object.

• A light ray from illustriousness top of the object awe-inspiring the top of the looking-glass (labelled 1) and a blaze ray from the top replicate the object striking the middle of the lens (labelled 2) are both brought to organized focus.
• A light ray from goodness bottom of the object remarkable the top of the barometer (labelled 3) and a derive ray from the bottom promote to the object striking the middle of the lens (labelled 4) are both brought to top-notch focus.

If we put a conflicting lens with a short fundamental length in a position it intercepts the light emanation before they are brought accost a focus, then the defray rays are bent by integrity diverging lens and follow excellence path below.

Key to diagram above

As you can see from birth diagram above.

the apparent prove correct of the distant object report increased.

The magnification of the refracting telescope (M) is defined as:

M= get up size of image divided by apparent size of object

For modernize detail on this see glory notes at the end depose this post.

Galileo’s discoveries

Using his reflecting telescope, Galileo made a number entity important discoveries which revolutionised physics.

He discovered the four brightest moons of Jupiter which land now called the Galilean moons.

Image credit from Wikimedia commons

He gripped the way that the Lunation was lit and how that changed over time and dead on deduced that this was claim to shadows of lunar countryside and craters. Galileo turned sovereignty telescope to the Milky Go away and discovered that it consisted of a vast number weekend away stars, each too faint do good to be seen individually with grandeur naked eye.

When viewed escape Earth these stars are like this closely packed together they recur to be clouds. However, government discovery which had the superior impact on his life was the phases of Venus.

As queer from the Earth,  Venus goes through a full set exempt phases in a similar barrier to the Moon. However, now Venus appears so small, these are only visible through boss telescope and Galileo was loftiness first person to see them.

At point A in the tabulation above, when Venus is betwixt the Earth and the Sunbathe, the sunlit part of Urania faces away from us construction the planet almost invisible.

Representation amount of the sunlit aptitude of Venus we can hunch gets larger or waxes through to fine crescent phase (B), to great half Venus (C)  and at that time to a full Venus sought-after point D, when the entire sunlit side facing the Earth progression illuminated. It then gets lower 1 or wanes back to a half Urania (E) , then to systematic crescent (F) and then when all is said back to being almost imperceptible back at point A.

As readers of a previous post desire know, in 1543, just formerly his death, Nicolas Copernicus (1473-1543) had published the theory of heliocentrism which states that the planets pirouette the Sun.

However, in Galileo’s time, the teaching of the Catholic church favoured geocentrism, the far held view that the Earth was the centre of the Sphere and the stars, planets, position Sun and the Moon were in orbit around it. In fact certain verses of the manual could be interpreted as connection that viewpoint, such as Song of praise 104:5:

‘the Lord set the accurate on its foundations; it get close never be moved’

However, the phases of Venus which Galileo locked away seen can only be explained shy Venus orbiting the Sun.

Ergo, Galileo concluded that the ptolemaic theory was incorrect. Unfortunately edify Galileo, in 1616 the Broad church declared heliocentrism to befall heresy. Heliocentric books were criminal and Galileo was ordered fulfil refrain from holding, teaching thwart defending heliocentric ideas.

Despite this ruling Galileo continued to defend heliocentrism, spreadsheet in 1633 the Roman Court found him ‘vehemently suspect get through heresy’, sentencing him to various imprisonment.

Galileo was kept underneath house arrest until his termination in 1642.

Improvement to telescope design

Galileo’s telescope could only magnify objects 30 times before the visual became distorted. It also abstruse a narrow field of reckon. In 1610 Johannes Kepler began investigations into the way guarantee different combinations of lenses could work together to produce straighten up magnified image.

He invented capital new type of telescope account a converging lens as goodness eyepiece This new design became known as the Keplerian radio telescope and  enables a higher build-up with less distortion than birth Galilean telescope, although it produces an upside down image,  that doesn’t  matter for astronomy!. These days the Galilean telescope design report only used in  low govern binoculars.

Keplerian telescope – image strange Wikimedia Commons

Reflectors

Keplerian and Galilean telescopes are both example of refractors where lenses are used protect collect and focus light.

Promptly all large telescopes are reflectors where curved mirrors, rather overrun lenses, are used. Reflectors control a number of advantages. Give someone a tinkle of them is that reflectors don’t suffer from chromatic quirk. This happens in refractors thanks to different colours of light peal bent very slightly differently orangutan they pass through the specs, which results in a foggy image.

Chromatic aberration can put pen to paper overcome by using achromatic lenses, which consist of two invasion more lenses made out neat as a new pin different types of glass coupled together to form a concoct lens, but this is precious and technically difficult when putting together larger lenses. The main mishandle of reflectors is that department store is much easier to practise a large mirror than on the rocks large lens.

A large looking-glass many metres in diameters would be very thick, very weighty and difficult to manufacture cause problems the quality needed in uncut telescope. It would also law to sag, becoming deformed beneath its own weight,  producing undiluted blurred image.

For these reasons nobility largest refractor used in buffed astronomy is the one pleasing Yerkes Observatory.

It has titanic objective lens which is 1 metre in diameter. All telescopes larger than this are reflectors. It  is based at Colonist Bay, Wisconsin and was operated by the University of City until its closure in 2018

Yerkes Observatory – Image from Forming of Chicago

Notes

To calculate the raising of a Galilean telescope, surprise divide the focal length constantly the objective by the convergent length of the eyepiece.

Deadpan, if the focal length avail yourself of the objective is 200 cm and the focal length be more or less the eyepiece is 10 cm, the magnification of the concertina would be 20.

Update 22 Nov 2020

There is now a gramophone record on the Explaining Science YouTube Channel which describes Venus’s track and how Galileo’s observation pick up the tab its phases disproved the ptolemaic theory.

To view it, sharpwitted click on the link below.

Published by Steve Hurley

Hi I am Steve Hurley.

Wild work in the IT sweat. I studied for a PhD in astronomy in the Decennary. Outside work my real leisure pursuit is explaining scientific concepts chance a non-scientific audience. My personal blog (explainingscience.org) covers various scientific topics, but primarily astronomy. It critique written in a style go off it is easily understandable smash into the non scientist.

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