Teleskop
Dari Wikipedia bahasa Melayu
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Perkataan "teleskop" (dari bahasa Greek tele = 'jauh' dan skopein = 'mencari atau melihat'; teleskopos = 'berpandangan jauh') biasanya merujuk kepada teleskop optik, tetapi selain itu terdapat juga teleskop yang digunakan untuk kebanyakan spektrum sinaran elektromagnet dan untuk isyarat jenis lain.
Teleskop terdiri daripada 2 kanta iaitu kanta objektif dan kanta mata. Kanta objektif menumpukan sinar cahaya yang jauh lalu membentuk imej yang nyata, songsang dan mengecil di titik fokus kanta mata manakala kanta mata membesarkan imej kanta objektif itu.
Ciri imej terakhir ialah infiniti, maya, songsang dan lebih besar dari objek.
Jadual isi kandungan |
[Sunting] Sejarah
- Rencana utama: Sejarah teleskop
Teleskop pertama kemungkinannya adalah kanta kristal masyarakat Assyria[1], tetapi kanta Visby buat sementara waktu mencadangkan bahawa teknologi tersebut diketahui oleh orang Arab dan Parsi. Leonard Digges kadang-kala dianggap ciptaan bersama dengan ciptaan Inggeris pada zaman 1570-an, tetapi biasanya kredit untuk kumpulan teleskop pertama diberikan kepada pembuat kaca mata Belanda yang tidak dikenali kira-kira pada tahun 1608. Sesetengah menamakannya person sebagai Hans Lippershey (kk. 1570 – kk. 1619), tetapi Jacob Metius dan Zacharias Jansen juga mendakwa telah mencipta sebuah telescope pada waktu yang sama. Walaupun Lippershey tidak membuat teleskop yang pertama, dia telah mengeluarkannya.Galileo Galilei membuat teleskopnya sendiri pada tahun 1609, memanggilnya "perspicillum," dan kemudian menggunakan istilah "telescopium" dalam Bahasa Latin dan "telescopio" dalam Bahasa Itali (dari mana perkataan Bahasa Inggeris berasal).
Galileo is generally credited with being the first to use a telescope for astronomical purposes. Galileo's teleskop consisted of a convex object lens dan a concave eye lens, yang is universally called a Galilean teleskop (used as a viewfinder in many simple cameras). Later, Johannes Kepler described the optics of lenses (see his books Astronomiae Pars Optica and Dioptrice), including a new kind of astronomical telescope with two convex lenses (a principle often called the Kepler telescope). Optical interferometer arrays dan arrays of radio teleskop telah developed much more recently.
[Sunting] Jenis-jenis teleskop
Telescopes are frequently characterised by their design details, and usually named after the principal designer or designers of that type of telescope. For optical telescopes, especially optical astronomical telescopes, there are three main types:
- Teleskop terbias which uses solely an arrangement of lenses.
- Teleskop terbias which uses solely an arrangement of mirrors.
- Teleskop katadioptrik which uses a combination of mirrors and lenses.
Di mana teleskop digunakan untuk lihatan langsung oleh mata manusia, yang mana ia biasa menggunakan keping mata untuk melihat imej, dan kebanyakan,
Where the telescope is used for direct viewing by the human eye, then very few telescopes are pure reflectors, as it is usual to use an eyepiece to view the image, and most, if not all eyepiece design use an arrangement of lenses. Much astronomy is performed using photographic film or digital sensors which are usually used without an eyepiece, so for mechanised operation more telescopes are used as pure reflectors.
Untuk penerangan selanjutnya sila lihat Daftar jenis teleskop
[Sunting] Research telescopes
Kebanyakan teleskop kajian boleh dijalankan sebagai sebuah teleskop Cassegrain (pelosok fokal yang lebih panjang, dan a narrower field with higher magnification) or a Newtonian telescope (brighter field). They have a pierced primary mirror, a Newtonian focus, and a spider to mount a variety of replaceable secondary mirrors.
A new era of telescope making was inaugurated by the Multiple Mirror Telescope (MMT), with a mirror composed of six segments synthesizing a mirror of 4.5 meters diameter. This has now been replaced by a single 6.5m mirror. Its example was followed by the Keck telescopes with 10 m segmented mirrors.
The largest current ground-based telescopes have a primary mirror of between 6 and 11 meters in diameter. In this generation of telescopes, the mirror is usually very thin, and is kept in an optimal shape by an array of actuators (see active optics). This technology has driven new designs for future telescopes with diameters of 30, 50 and even 100 meters.
Relatively cheap, mass-produced ~2 meter telescopes have recently been developed and have made a significant impact on astronomy research. These allow many astronomical targets to be monitored continuously, and for large areas of sky to be surveyed. Many are robotic telescopes, computer controlled over the internet (see e.g. the Liverpool Telescope and the Faulkes Telescope North and South), allowing automated follow-up of astronomical events.
Initially the detector used in telescopes was the human eye. Later, the sensitized photographic plate took its place, and the spectrograph was introduced, allowing the gathering of spectral information. After the photographic plate, successive generations of electronic detectors, such as the charge-coupled device (CCDs), have been perfected, each with more sensitivity and resolution, and often with a wider wavelength coverage.
Teleskop kajian terkini ada banyak alat untuk dipilih seperti:
- imagers, of different spectral responses
- spectrographs, useful in different regions of the spectrum
- polarimeters, that detect light polarization.
Pada tahun recent, sesetengah technologies digunakan untuk menewaskan distorsyen dicausekan oleh atmosphere pada teleskop ground-based dideveloped, dengan hasilan bagus. Lihat adaptive optics, speckle imaging dan optical interferometry.
Fenomenon optical diffraction memberikan sebuah had ke kualiti resolusi dan imej sebuah teleskop can achieve, which is the effective area of the Airy disc, which limits how close two such discs can be placed. This absolute limit is called the diffraction limit (or sometimes the Rayleigh criterion, Dawes limit or Sparrow's resolution limit). This limit depends on the wavelength of the studied light (so that the limit for red light comes much earlier than the limit for blue light) and on the diameter of the telescope mirror. This means that a telescope with a certain mirror diameter can resolve up to a certain limit at a certain wavelength. If greater resolution is needed at that wavelength, a wider mirror has to be built or aperture synthesis performed using an array of nearby telescopes.
[Sunting] Imej Tak Sempurna
No telescope can form a perfect image. Even if a reflecting telescope could have a perfect mirror, or a refracting telescope could have a perfect lens, the effects of aperture diffraction could still not be escaped. In reality, perfect mirrors and perfect lenses do not exist, so image aberrations in addition to aperture diffraction must be taken into account. Image aberrations can be broken down into two main classes, monochromatic, and polychromatic. In 1857, Philipp Ludwig von Seidel (1821-1896) decomposed the first order monochromatic aberrations into five constituent aberrations. They are now commonly referred to as the five Seidel Aberrations.
[Sunting] Lima aberrasi Seidel
- Spherical aberration
- The difference in focal length between paraxial rays and marginal rays, proportional to the square of the aperture.
- Coma
- A most objectionable defect by which points are imaged as comet-like asymmetrical patches of light with tails, which makes measurement very imprecise. Its magnitude is usually deduced from the optical sine theorem.
- Astigmatism
- The image of a point forms focal lines at the sagittal and tangiental foci and in between (in the absence of coma) an elliptical shape.
- Curvature of Field
- The Petzval curvature means that the image instead of lying in a plane actually lies on a curved surface which is described as hollow or round. This causes problems when a flat imaging device is used e.g. a photographic plate or CCD image sensor.
- Distortion
- Either barrel or pincushion, a radial distortion which must be corrected for if multiple images are to be combined (similar to stitching multiple photos into a panoramic photo).
They are always listed in the above order since this expresses their interdependence as first order aberrations via moves of the exit/entrance pupils. The first Seidel aberration, Spherical Aberration, is independent of the position of the exit pupil (as it is the same for axial and extra-axial pencils). The second, coma, changes as a function of pupil distance and spherical aberration, hence the well-known result that it is impossible to correct the coma in a lens free of spherical aberration by simply moving the pupil. Similar dependencies affect the remaining aberrations in the list.
[Sunting] Aberrasi kromatik
- Longitudinal Chromatic Aberration
- As with spherical aberration this is the same for axial and oblique pencils.
- Transverse Chromatic Aberration (Chromatic Aberration of Magnification)
[Sunting] Teleskop optikal termasyur
- Teleskop Angkasa Hubble is in orbit beyond Earth's atmosphere to allow for observations not distorted by astronomical seeing. In this way the images can be diffraction limited, and used for coverage in the ultraviolet (UV) and infrared.
- Teleskop Keck are currently (seperti pada tahun 2005) the largest, but will soon be superseded by the Gran Telescopio Canarias and Southern African Large Telescope.
- The Very Large Telescope array (VLT) is currently (as of 2002) the record holder for total collecting area in an array of telescopes, with four telescopes each 8 meters in diameter. The four telescopes, belonging to the European Southern Observatory (ESO) and located in the Atacama desert in Chile, are usually operated independently for faint astronomical observations, but up to three telescopes can be operated together for aperture synthesis observations of bright objects.
- The Navy Prototype Optical Interferometer is the optical telescope (array) that can currently (as of 2005) produce the highest resolution images at visible wavelengths.
- The CHARA (Center for High Angular Resolution Astronomy) array is the telescope array that can currently (as of 2005) produce the highest resolution images at near-infrared wavelengths.
- There are many plans for even larger telescopes. One of them is the Overwhelmingly Large Telescope (OWL), which is intended to have a single aperture of 100 meters in diameter.
- The 200-inch (5.08-meter) Hale telescope on Palomar Mountain was the largest conventional research telescope for many years. It has a single borosilicate (Pyrex™) mirror that was famously difficult to construct. The mounting is a special design of equatorial mount called a yoke mount, which permits the telescope to be pointed at and near the north celestial pole.
- The 100-inch (2.54-meter) Hooker Telescope at the Mount Wilson Observatory was used by Edwin Hubble to discover galaxies and the redshift. The mirror was made of green glass by Saint-Gobain. In 1919, the telescope was used for the first stellar diameter measurements using interferometry. The telescope now has an adaptive optics system, and is still useful for advanced research.
- The 72-inch Leviathan at Birr Castle (in Ireland) was the largest telescope in the world from 1845 until it was dismanlted in 1908. It was not exceeded in size until the construction of the Hooker Telescope.
- The 1.02-meter Yerkes Telescope (in Wisconsin) is the largest aimable refracting telescope in use.
- The 0.76-meter Nice refractor (in France) that became operational in 1888 was at that time the world's largest refractor. This was the last time the most powerful operational telescope in the world was located in Europe. It was exceeded in size one year later by the 0.91-meter refractor at the Lick Observatory.
- The largest refractor ever constructed was French. It was on display at the 1900 Paris Exposition. Its lens was stationary, prefigured so as to sag into the correct shape. The telescope was aimed by the aid of a Foucault sidérostat, which is a movable plane mirror with a 2-meter diameter, mounted in a large cast-iron frame. The horizontal tube was 60 m long and the objective had 1.25 m in diameter. It was a failure.
- The Gran Telescopio CANARIAS ( Grantecan, also GTC), is a high performance segmented 10.4 meter telescope that is being installed in one of the best sites of the Northern Hemisphere: the Roque de los Muchachos Observatory (La Palma, Canary Islands, Spain).
- The 1-meter refracting Swedish Solar Telescope (SST) on La Palma (Spain), is currently the highest-resolution solar telescope in the world.
[Sunting] Teleskop termasyur lain
- Arecibo Observatory
- Atacama Large Millimeter Array
- Very Large Array
- Chandra X-ray Observatory
- XMM-Newton
- LIGO
- IceCube Neutrino Detector
- Isaac Newton Telescope
- William Herschel Telescope
[Sunting] Lihat juga
- Amateur telescope making
- Aperture synthesis
- ASCOM open standards for computer control of telescopes
- Binoculars
- Depth of field
- Dynameter
- Eyepiece
- First light
- f-number
- History of telescopes
- List of largest optical reflecting telescopes
- List of largest optical refracting telescopes
- Maksutov telescope
- Microscope
- Optical telescope
- Radio telescope
- Reflector telescope
- Refracting telescope
- Robotic telescope
- Timeline of telescope technology
- Timeline of telescopes, observatories, and observing technology
