“Traian” Highschool, Constanta, RomaniaA project realized by: Andreiev Vasile

Apetroaie ClaudiuDobre AlexandruDeoanca RaresFlorea Andrei, Ganescu Andrei

Teacher: Tanasescu Gabriela Violeta

The earliest known working telescopes appeared in 1608 and are credited to Hans Lippershey. Among many others who claimed to have made the discovery were Zacharias Janssen, a spectacle-maker in Middelburg, and Jacob Metius of Alkmaar. The design of these early refracting telescopes consisted of a convex objective lens and a concave eyepiece. Galileo used this design the following year. In 1611, Johannes Kepler described how a telescope could be made with a convex objective lens and a convex eyepiece lens and by 1655 astronomers such as ChristiaanHuygens were building powerful but unwieldy Kepleriantelescopes with compound eyepieces. Hans Lippershey is the earliest person documented to have applied for a patent for the device.

Isaac Newton is credited with building the first "practical" reflector in 1668 with a design that incorporated a small flat diagonal mirror to reflect the light to an eyepiece mounted on the side of the telescope. Laurent Cassegrain in 1672 described the design of a reflector with a small convex secondary mirror to reflect light through a central hole in the main mirror.

The achromatic lens, which greatly reduced color aberrations in objective lenses and allowed for shorter and more functional telescopes, first appeared in a 1733 telescope made by Chester Moore Hall, who did not publicize it. John Dollond learned of Hall's invention and began producing telescopes using it in commercial quantities, starting in 1758.

Important developments in reflecting telescopes were John Hadley's production of larger paraboloidal mirrors in 1721; the process of silvering glass mirrors introduced by Léon Foucault in 1857; and the adoption of long lasting aluminized coatings on reflector mirrors in 1932. Almost all of the large optical research telescopes used today are reflectors.

The era of radio telescopes (along with radio astronomy) was born with Karl Guthe Jansky's serendipitous discovery of an astronomical radio source in 1931. Many types of telescopes were developed in the 20th century for a wide range of wavelengths from radio to gamma-rays.

Lastest kind of telescopes are Radio Telescopes

Radio astronomy began in 1931 when Karl Jansky discovered that the Milky Way was a source of radio emission while doing research on terrestrial static with a direction antenna. Building on Jansky'swork, Grote Reber built a more sophisticated purpose-built radio telescope in 1937, with a 31.4 feet (9.6 m) dish; using this, he discovered various unexplained radio sources in the sky.

Interest in radio astronomy grew after the Second World War when much larger dishes were built including: the 250 feet (76 m) Jodrell bank telescope (1957), the 300 feet (91 m) Green Bank Telescope (1962), and the 100 metres(330 ft) Effelsberg telescope (1971). The huge 1,000 feet (300 m)Arecibo telescope (1963) is so large that it is fixed into a natural depression in the ground; the central antenna can be steered to allow the telescope to study objects up to twenty degrees from the zenith. However, not every radio telescope is of the dish type. For example, theMills Cross Telescope (1954) was an early example of an array which used two perpendicular lines of antennae 1,500 feet (460 m) in length to survey the sky.

High-energy radio waves are known as microwaves and this has been an important area of astronomy ever since the discovery of the cosmic microwave background radiation in 1964. Many ground-based radio telescopes can study microwaves. Short wavelength microwaves are best studied from space because water vapor (even at high altitudes) strongly weakens the signal. The Cosmic Background Explorer (1989) revolutionized the study of the microwave background radiation.

Because radio telescopes have low resolution, they were the first instruments to use interferometry allowing two or more widely separated instruments to simultaneously observe the same source. Very long baseline interferometry extended the technique over thousands of kilometers and allowed resolutions down to a few milli-arcseconds.

A telescope like the Large Millimeter Telescope (active since 2006) observes from 0.85 to 4 millimetres (850 to 4,000 µm), bridging between the far-infrared/submillimeter telescopes and longer wavelength radio telescopes including the microwave band from about 1 mm (1000 µm) to 1000 mm (1 meter) in wavelength.

Adaptive optics

Adaptive optics (AO) is a technology used to improve the performance of optical systems by reducing the effect of wavefront distortions: it aims at correcting the deformations of an incoming wavefront by deforming a mirror in order to compensate for the distortion. It is used in astronomical telescopes and laser communication systems to remove the effects of atmospheric distortion. Adaptive optics works by measuring the distortions in a wavefront and compensating for them with a device that corrects those errors such as a deformable mirror or a liquid crystal array.Other methods can achieve resolving power exceeding the limit imposed by atmospheric distortion, such as speckle imaging, aperture synthesis, and lucky imaging, or by moving outside the atmosphere with space telescopes, such as the Hubble Space Telescope.

A project realized with VioletaTanasescu’s support