People used to look up at both daytime and night sky since their existence on this planet. They were attracted by its beauty at night, but also intrigued by the real nature of all those different celestial objects which could be seen. Unfortunately except enjoying the views they did not know anything about the sky. They did not know anything about the Sun and the Moon, anything about the planets which moved slowly against the starry background on the sky every night, and anything about the stars and other phenomena, like sudden supernova or comet appearance from time to time which scared them. They were able to recognize several so-called deep-sky celestial objects on the sky - a few open clusters, globular clusters and galaxies, which are visible with naked eye like small whitish clouds on the night sky, but did not know their real nature. 
          In ancient times, there were some individuals - philosophers, mathematicians and astronomers who devoted much of their time and knowledge trying to solve the mysteries of the universe. They observed and wrote on paper the movement of the Sun, the Moon and the planets, drew pictures of the comets and supernovae that appeared on the sky with exact times and positions, they recorded the transits of Venus and Mercury in front of the Sun, the Sun and Moon eclipses, described the colors of the stars and their approximate brightness and a lot of other things. Also there were first attempts based on this drawings and recordings to calculate the diameter of the Earth, the diameter of the Sun, the distance between the Earth and the Moon and planets. They concluded that the Earth is round and not flat, that the Earth and other planets orbit around the  Sun. Also there were attempts to explain the physical nature of the Sun, the stars and the other several visible with naked eye celestial objects that were different than the stars.
          In 1610 the telescope was invented - made of small lenses which could magnify several times the objects observed through it. Galileo Galilei (1564-1642) was among the first to order one and point it towards the sky. That was dramatic moment in astronomy - he could see several satellites around the Jupiter and noticed that every night they change their position against Jupiter - he concluded that they orbit around Jupiter. He also observed the Sun spots and also was able to see more stars through the telescope at night than he could see with naked eye. Suddenly the universe become much bigger than previously thought and with more questions to be answered and solved. Theoretical physicists were able to solve the mysteries of our Solar system - the Sun was big object in the center of our solar system, and the planets were orbiting around the Sun with the furthest planet needed the longest time to make one orbit. But the practical observing of outer planets showed that their movement is a bit different than the theory predicted - astronomers assumed that there must be other bodies in our Solar system that gravitationally interact with the known planets and alter their movement not to match with their mathematical movement. The hunt for the planets started - and planet Neptune was discovered in 1781 and dwarf planet Pluto in 1930.
          Another big moment for the astronomy was the invention of another type of telescope - in 1668 Sir Isaac Newton (1642-1726) built a telescope using a small mirror (made of reflective metal alloy) instead of lens. He made the mirror by himself and properly stated that the shape of its surface must be paraboloidal in order to give sharp image of the objects, but the technology of the polishing materials could not enable him to make perfect mirrors. Except in the optics, also notable is to mention that Newton made discoveries in other fields of the science - motions of the bodies, gravitation etc. which when applied in astronomy could explain the movement of the celestial bodies in the universe.
          With a telescope astronomers were able to find and observe more celestial objects. Some astronomers started keeping records of their observing and publish the first catalogs of deep-sky objects. By far the most popular catalog was that one published by French astronomer Charles Messier (1730-1817). Most of the objects were discovered by him with his 4-inch refractor telescope, but also other astronomers submitted their discoveries to him to be included in the catalog. This catalog is popular even today and in use especially by amateur astronomers and contains 110 deep-sky objects and is known as Messier catalog. It contains almost all brightest and biggest, that means the most beautiful deep-sky celestial objects visible from the Northern hemisphere. With such small telescopes at that time, both Messier and other astronomers were only able to detect these objects like small clouds of stars - they were not able to see and enjoy all their beauty as we can with today's big telescopes.
          Soon after opticians were able to make bigger and bigger mirrors to be used in a telescope. Interesting is that at first the mirrors, including Newton's were made from metal alloy, not from glass. Their reflectivity was poor. Bigger telescopes enabled astronomers to observe dimmer celestial objects on the night sky. Now they were able to see better all that blurry objects which were something like clouds of stars, like nebulosity. But still they were not able to pinpoint their true nature. Astronomers were not sure how far and how big they are, and only estimated that they are further from the stars, but not very far. 
          Another person who made significant contribution to astronomy was Sir William Herschel (1738-1822). He was musician born in Germany and moved to Great Britain, but became also interested in astronomy and started making his own mirrors and telescopes. In 1774 he made as he described at that time big 6-inch mirror (still metal alloy). In the next years he started observing and exploring the sky systematically and recorded all his observations. He also discovered the planet Uranus. He observed double stars but also a lot of before mentioned objects which looked like clouds of stars. He give the name nebulae to this objects. Herschel was also famous mirror maker and telescope builder and observed the sky with his telescopes, one with almost 19 inch diameter mirror. He discovered several thousands of such nebulae in the next years and even started publishing catalogs. In his catalogs he divided the nebulae on several categories - bright, faint, very faint, large, small, and also on clusters of compressed stars and clusters of scattered stars. His catalogs and discoveries are base for today's very popular catalog of celestial objects amateur and professional astronomers use - so called the New General Catalogue (NGC) of 7840 deep-sky objects. In 1888 NGC catalogue was published for the first time including the objects Herschel discovered, together with discovered objects from his son and many objects discovered from other astronomers in the following years. Herschel also concluded that our Solar system is moving through the space and also introduced the word asteroid for small bodies in our solar system which cannot be seen as disc in the telescope (contrary to the planets which can be seen as discs in telescope).
          Amateur astronomers were also buying telescopes, which were very expensive at that time, to observe the sky and enjoy the views of the celestial objects. At the same time they made a lot of discoveries and contributions to astronomy. Some of them were making mirrors and building telescopes by themselves. One of them was William Parsons, the third Earl of Rosse (1800-1867). He made several mirrors and build several telescopes, each bigger than the previous. In 1845 he finished a telescope with 72-inch mirror (still made from metal alloy) which was the largest telescope in the world in the 19th century and until the early 20th century. The telescope could better reveal the structure of the nebulae - his telescope was first to reveal that some of the nebulae have spiral arms (today we know that these objects are spiral galaxies). Parsons made drawing of all these objects he was observing. He also discovered a lot of other up to then undiscovered deep-sky objects - he contributed over 200 new deep-sky objects to the NGC catalog. 
          Another important things to be mentioned were introduction of the spectrometry and astrophotography. Newton first noticed that a white light after passing through a prism showed spectrum of colors, but will be long time after when spectrometers will be used to study the chemical composition, temperature and other properties of the stars and celestial objects. The same was with the astrophotography. Around 1850 the first successful photograph of the Moon was made, and also of the Sun and the Sun eclipse which showed the Sun's corona. In 1880 Henry Draper (1837-1882) made the first photograph of a nebula ever, the Orion Nebula. Several years later one amateur astronomer - Andrew Common - imaged the same nebula with his 36-inch telescope he built by himself including the mirror (glass mirror), and the image showed stars which could not be seen with naked eye through the same telescope. Suddenly again the universe become bigger than was previously thought. And today - today we all know the well-known images of the Hubble Space Telescope, with the newly installed CCD camera it is capable of imaging galaxies and other faint objects located at the edge of our known universe, 13 billion light years away from the Earth.
          Last hundred years are years of great advancement and discoveries in all sciences, including astronomy science. Probably 99% of the knowledge in astronomy was acquired in the last hundred years. Eighty years ago scientists still did not know what kind of process is going on inside our Sun to make it such powerful source of energy. Today we know that it is the nuclear fusion of hydrogen into helium. And hundred years ago astronomers were still thinking that all stars and deep-sky objects we could see on the sky are part of our own galaxy and that they are relatively close. Yes, the whole universe at that time was thought to be only our galaxy. But Edwin Hubble (1889-1953) made one of the biggest discoveries in astronomy in the 20th century. He was working at Mount Wilson Observatory and was studying the nebulae, especially the spiral nebulae with the biggest telescope at that time - with 2.5 meter mirror diameter. He proved that spiral nebulae are much further than previously thought, and as such they can not be part of our galaxy, but in fact they are separate galaxies like our own galaxy. Suddenly, again the universe became hundreds times bigger than was previously thought. Before Hubble discovery, the whole universe was thought to consist of our galaxy and all celestial objects we could see on the sky and on astroimages was thought that are inside our galaxy  But with the Hubble discovery, now we know that the universe consists of our own galaxy, plus billions of other galaxies more or less similar to our with the furthest ones some 13 billion light years away from the Earth. Several years later studying these galaxies Hubble even proved that the universe is expanding. Today's Hubble Space Telescope is named after this great astronomer and scientist.
          Today's astronomy , like other sciences, has split into more than ten branches - some observational and some theoretical branches. Astronomy is not anymore only observing and writing notes about what is happening on the sky. It has interfered with other sciences in order to cover the research about the stars and other celestial objects, their physics and mechanics, their composition, their evolution, the possibility of life in the universe, building of research instruments. Separate branch of astronomy only study our Sun, and separate branch of astronomy only study the planets including the exoplanets and so on. Astrophysics become equally important in studying the celestial objects. Today in every bigger city on the planet we have university with astronomy department where some branch of astronomy is studied. They also operate hundreds of observatories all over the world, with the largest of them with mirrors from four to up to ten meters in diameter mostly located on Hawaii and Chile where there is no light pollution and most of the days in the year the sky is clear. Astronomers together with other scientists also build astronomy instruments which will be installed on the spacecrafts to study the celestial objects from space. Today tens of thousands of scientists work in many fields of astronomy.
          Today, with our knowledge and our instruments we have reached the edge of the universe, thanks to astronomy science. But it is hard to believe that our knowledge and discoveries will stop there. They never stopped and will not stop. There will be a lot of new discoveries and new theories in the coming years. That's why, maybe it is better only to say that we have reached the edge of our known universe. As some scientists propose, and many other agree, our known universe can be part of an unknown for now multiuniverse, where billions of universes like our own also exist, and our is only one of billions. 
          (to continue with learning click on ABOUT button on the main menu)                                                      June 2015, Toronto