1. Telescopes

2. Earliest Mention of Telescope
Leanord & Thomas Diggs s Son publishes book
“…by proportionall glasses duely situate in convenient angles, not onely discovered things farre off …”

3. By 1609 – telescopes can be bought in spectacle-makers shops in Paris
Annual fair at Frankfurt - telescope for sale with convex & concave lens, magnifies 7X
October 2, 1608 – Johann Lippershey of Middleburg in the Netherlands files a patent for a telescope
By 1609 – telescopes can be bought in spectacle-makers shops in Paris
Lippershey was denied a patent because of the difficulties in establishing his priority for the invention and because it was too easy to copy. However, he was asked by the Dutch government to produce a 'two-eyed' version of the telescope - we now call them binoculars - and in 1609 spy-glasses were actually on-sale in Paris! They gave upright images and were intended for terrestrial use. Interestingly, there is a note in a brochure, dated November 22, 1608, that says that a telescope could also be used for "seeing stars which are not ordinarily in view because of their smallness"

4. Harriot is also the 1st to record sunspots December 1610
Thomas Harriot – 1609
His drawing of the moon is the first on record, beating Galileo’s by several months
Nothing is known of Harriot's life up to the time when, at age seventeen, he matriculated at the University of Oxford. The record states that he was from the county of Oxford and that his father was a commoner. Harriot studied at St. Mary's Hall, took his degree in 1580, and went to London. Here he was employed by Sir Walter Ralegh and in 1585 went with the expedition to Virginia organized by Ralegh as cartographer and one versed in the theory of navigation--in our terms, as staff scientist. Harriot returned in 1586 and wrote an account of Virginia and its natives, A Briefe and True Report of the New Found Land of Virginia , published in In the meantime, Harriot had joined Ralegh in Ireland, which the English were colonizing at that time. Ralegh granted Harriot a former abbey, where Harriot lived for a few years. Back in London, Harriot came into contact with William Percy, 9th Earl of Northumberland, and in 1598 he left Ralegh and entered the service of Northumberland, who gave him a pension and living quarters (and later a separate house) at Syon House, just west of London. In 1605 Harriot was briefly imprisoned along with Northumberland as a result of the Gunpowder Plot. Harriot was quickly released but the earl remained in the Tower of London until Harriot lived at Syon for the rest of his life. In 1613 he developed an cancerous ulcer (on his nostril), which was the eventual cause of his death. Except for A Brief and True Report, Harriot published no books. At his death he left a large number of manuscripts on various scientific subjects, and over the past three centuries these have slowly come into the mainstream of historical research. Harriot studied optics (about which he corresponded with Johannes Kepler) and, he made important contributions to algebra, and, from 1609 to 1613, he made numerous telescopic observations. His telescopic drawing of the Moon of early August 1609 is the first on record and preceded Galileo's study of the Moon by several months .
Harriot is also the 1st to record sunspots
December 1610
BUT he does not publish

5. 1609-1610 Galileo studies variety of celestial objects
Using his telescopes Galileo studied a variety of objects in the solar system beginning in the winter of Actually, he refers (in Latin) to his device as a 'perspicillum' often translated as 'spyglass'; the word telescope was not coined until the year 1611.
In December 1609 he made detailed observations of the moon, see figure 10. He measured the heights of mountains from the shadows, and found some were several miles high. It was, of course, this type of observation and conclusion that set him head and shoulders above his contemporaries.
Early in January 1610 he discovered 4 moons orbiting Jupiter, see figure 11. As I mentioned earlier, he was wanting to return to Tuscany and so in order to re-ingratiate himself with the Medici family, who were the Grand Dukes of Tuscany, he first called the group the Medicean planets and named the moons after the Medici children. Although the Medici's were impressed, it was not well received generally and shortly after they became known as the Galilean moons and were re-named Io, Europa, Ganymede and Callisto.
Early in March 1610 Galileo published these discoveries in his Siderius Nuncius (Starry Messenger) dedicated to Grand Duke Cosimo de' Medici of Tuscany. Not surprisingly, having expressed a strong desire to return to Tuscany and having flattered the Duke, he was appointed as chief mathematician and physicist to the Grand Duke with a non-teaching appointment at the University of Pisa. He moved to Florence in September 1610 having sent his daughters (then aged eight and ten years) there earlier to be with his mother and leaving his son (aged four years) with Marina Gamba until he was old enough to leave her care.
Chief among his discoveries, published in Siderius Nuncius,, were:
A 'rough' moon was entirely inconsistent with Aristotelian philosophy that required all heavenly bodies to be pure, i.e, perfect spheres. Although he and his supporters did their best to convince clerics that the moon did indeed have mountains, the contrary argument they put forward was that since the mountains disappeared when the telescope was removed they must be an artifact of the lenses!
Orbiting moons around Jupiter that contradicted the idea of natural philosophers that the Earth was the center of all celestial motions.
He also determined that the Sun was not 'pure' - it was 'spotty' - and that it took about 3-4 weeks to spin on its axis, see figure 12.
Soon after arriving in Florence, he also found that Venus was a planet, with phases like the moon, proving conclusively that Venus revolved not around the Earth but around the Sun.
Almost everything he looked at seemed to contradict the earth-centered theory of Ptolemy and the 'perfect' models of Aristotle but these discoveries had put him in serious danger and he was beginning to get himself into very deep water with the Catholic Church. In fact, he and his colleagues used to send coded messages and anagrams to each other to announce their findings and to ensure that they would be properly credited later with their discoveries! (Anagrams and coded messages were similarly used by both Newton and Huygens.)

6. 1672 Isaac Newton - Reflecting Telescope
A Scottish astronomer, James Gregory, came up with the design for the reflecting telescope in Newton was bothered by chromatic aberation – colors that appeared at the edges of images made with lenses. Isaac Newton made the first model of the reflecting telescope in 1688.
Chromatic Aberration

7. What kind of lens? What kind of mirror?
Concave
Convex

8. Things to explore with the light box
How does light behave with a concave lens?
How does light behave with a convex lens?
How does light behave with a flat mirror?
How does light behave with a concave mirror?
How does light behave with a convex mirror?
Why are things upside down in a telescope?
Why are things magnified in a telescope?
What is chromatic aberration?

9. Concave Convex
Lens
Mirror

10. Mirror
The law of reflection says that a light ray and its reflection make equal angles with the normal to the reflecting surface                    
Lens
James Harriot discovered some of these principles and had discovered what is now known as Snell's Law of refraction before Snell did.
When light travels from one medium to another, it generally bends, or refracts. The law of refraction gives us a way of predicting the amount of bend. This law is more complicated than that for reflection, but an understanding of refraction will be necessary for our future discussion of lenses and their applications. The law of refraction is also known as Snell's Law, named for Willobrord Snell, who discovered the law in 1621.
Snell's Law
Like with reflection, refraction also involves the angles that the incident ray and the refracted ray make with the normal to the surface at the point of refraction. Unlike reflection, refraction also depends on the media through which the light rays are travelling. This dependence is made explicit in Snell's Law via refractive indices, numbers which are constant for given media1.
Snell's Law is given in the following diagram.
As in reflection, we measure the angles from the normal to the surface, at the point of contact. The constants n are the indices of refraction for the corresponding media.
Refraction involves the angles that the incident ray and the refracted ray make with the normal to the surface at the point of refraction

11. How do lenses & mirrors work in a telescope?

12. Refracting Telescopes
The convex/concave combination is the same type of instrument refined and used by Galileo for his ground - breaking observations and is today known as the Galilean telescope and is shown in the top diagram of figure 4.
Actually, the Galilean telescope was quickly abandoned for other types, in particular the design suggested by Johannes Kepler. This Keplerian telescope (bottom, figure 4) employs a converging lens as the eyepiece and gives a wider field of view (i.e., takes in more of the sky ) than the Galilean arrangement. Its main disadvantage is that the resulting image is upside down, but it was quickly realized that this is has no significance in astronomical observations.
Telescopes which use a lens as the objective are known as refracting telescopes or simply refractors. The second major type of telescope employs a curved mirror as the objective. This is known as a reflecting telescope or reflector. The reflecting telescope was suggested by Leonard Diggs in the late 1500s, but the first practical design was demonstrated by Isaac Newton in 1671.

13. Why does a Concave or Diverging Lens
Convex Mirror
Shrink Images?
Angle of Reflection = Angle of Incidence  Angles are measured with  respect to the normal line  (the perpendicular line).

14. Why does a Convex or Converging Lens
Concave Mirror
magnify images?

17. Objective lens has longest focal length; eye piece has shorter focal length
What is "focal length?" The "focal length" of a lens is the distance between the optical center of the lens and the place where it focuses its image.

18. Magnification is defined as (angle subtended by image)/(angle subtended by object). In an astronomical telescope this is almost exactly the same as (focal length of objective)/(focal length of eyepiece).
Magnification = F / f