The first time human beings watched the sky was before 1600. There was no artificial equipment for sky watching, just eyes. A telescope was invented in the beginning of 1600. Galileo Galilei used a telescope since 1609. Later in the end of 1600 Isaac Newton developed a mirror telescope. In the end of 1800 photographing equipment were connected with telescopes, which started a new era in astronomy. Various technological innovations were born in the beginning of 1900, but the real growth of astronomy started in the end of 1960 because of computer aided systems.

Our planet's atmosphere causes headache for astronomers because it filters out most of the radiation from the space. The problem is that only a fraction of the electromagnetic radiation gets through the atmosphere. Only visible light (vawelength 300-800 nm) and radiovawes (1 mm - 15 m) can be detected down on Earth. Additional problems are caused by refraction and scintillation. These phenomena can be seen when using a telescope. A star looks like a "disk". Those atmospheric phenomena force us to select carefully the locations for telescopes. The best places for observatories on our planet are in Chile, Hawaii and the Canary Islands.

There are two types of optical telescopes, namely refractors (dioptrics) and reflectors (catoptrics). Refractors use lenses whereas reflectors use mirrors. The basic idea of an optical telescope is to gather and focus light mainly from the visible part of the electromagnetic spectrum. Refractors behave much as camera objectives, whereas reflectors create the image in the focal point of the telescope. There are various combinations and configurations of the telescopes, such as Newton and Cassegrain telescopes.

The first astronomical images were taken somewhere in late 1800. Nowadays CCD- (Charged-Coupled Device) cameras provide many times better images than those regular cameras.

Here are few big telescopes around the world:
- Mauna Kea
- Gemini
- Harlan J. Smith

Let's talk about the two types of telescopes, namely refractors and reflectors. According to Wikipedia, a telescope is "an instrument designed for the observation of remote objects and the collection of electromagnetic radiation". In fact this means that the purpose of telescopes is to gather light. The bigger the surface area of the lens of the telescope, the more photons the telescope gathers. The reason for building massive telescopes is to gather more and more photons, which means to be able to see further.

The name "telescope" was invented by Galileo Galilei in 1611. In Greek "tele" = far, "scopein" = to look or see, "teleskopos" = far-seeing [Wikipedia]. The name "telescopes" actually covers more devices than just optical reflectors and refractors. Optical telescopes, radio telescopes, and X-ray and gamma-ray telescopes all belong under the name "telescopes". I concentrate in this article to optical telescopes, and especially to reflectors and refractors.

A rafracting telescope uses a lens to gather photons and it works pretty much like a lens camera. Refraractors were the first telescopes invented. The first real refractors did exist in the beginning of 1600 in the Netherlands. A reflecting telescope uses mirrors to gather light and form an image. The first practical reflecting telescopes were built in late 1600 by Isaac Newton. Refractors are mainly used by amateurs, while reflectors are popular in professional astronomy.

Newton type reflector was invented by Isaac Newton. It includes a small mirror inside the telescope to redirect the light to either side of the instrument. By this arrangement a user can observe the image from the side of the telescope. The picture above is an example of a Newtonian telescope. A Cassegrain type reflector includes a small mirror inside to redirect the light back towards the main mirror. The light goes through a small hole in the middle of the main mirror and hits a detection system in the end of the telescope. The detection system is usually a CCD- (Charged-Coupled Device) camera which is able to collect almost each incoming photon. Scientists use CCD-cameras to study the brightness and spectrum of objects.

Optical telescopes are used to create a picture of the objects in the space, but the problem with them is that they cannot "see" far. In order to see very far, such as billions of light years away from the Earth, we need other types of tools. Radiotelescopes provide us a possibility to see very far from our planet. Radioastronomy was born in 1930's when American Karl Jansky suddenly captured radio signals from space. He realized that the signal comes from the same direction every day, but the astronomers did not put much attention to this phenomenon.

Although astronomers did not get interested, there was one man who got, Grote Reber. He built his own radiotelescope and found dozens of sources of radio signals in space. Bigger and higher performing telescopes were built in 1960's.

The first big and fully rotating radiotelescope was built in Jodrell Bank in England. The telescope was ready 1957 and its diameter is 76 meters. This telescope is still in use, after 50 years of operation. The next big telescope was built by NRAO (National Radio Astronomy Observatory in US) in the end of 1950's. It was a bit bigger than the one in Jodrell Bank but it suddenly collapsed. NRAO built a new and even bigger telescope, Green Bank, which has a size of 100×110 meters. The biggest radiotelescope on Earth is Arecibo telescope in Puerto Rico and its diameter is 300 meters. Other locations of radiotelescopes are La Silla in Chile, Mauna Kea in Hawaii, and Nobeyama in Japan.

Individual radiotelescopes are not able to "see" enough and therefore new solutions are needed. Radiotelescope arrays were invented around 1970's to address this problem. An array is a group of individual radiotelescopes connected with each other. Together they can provide even better results. The first big array was built in Cambridge and it is five kilometers long. The biggest array today is VLA (Very Large Array) which was built in New Mexico in the end of 1970's. It consists of 27 telescopes that can be moved on rails. Diameter of this telescope array is 40 kilometers and the individual telescopes are connected to each others by cables.

VLA is big but it is possible to build even bigger one by connecting telescopes by radio channels. VLBA (Very Large Baseline Array) has a diameter of 8000 kilometers and it is located on North American soil. Again, VLBA is big. Actually it is huge, but there are plans to build even bigger array. By positioning telescopes on Earth and in space we can get thousands times sharper images than today's optical instruments can provide.

Hold on! There is even bigger array. After publishing this article, Stuart as one of my readers, pointed out the following:

Actually, the largest radio telescope array in use today is called global VLBI and involves connecting the VLBA and the European VLBI network (EVN) with telescopes in Australia and several other countries. This gives a telescope the diameter of the planet Earth. At one point it also included the Japanese satellite Halca making a radio telescope effectively three times the diameter of the Earth.

As you can guess, the future is for radioastronomy.