8/13/2023 0 Comments Spectra definition in scienceThe next generation of spectrographs, like those planned for the Extremely Large Telescope (ELT), will go beyond anything we can currently achieve. But HARPS, installed on the ESO 3.6-metre telescope, is certainly one of the most famous for its leading role in the detection of exoplanets. Some spectrographs at the Very Large Telescope in Paranal produce high-resolution spectra like UVES and CRIRES others obtain spectra of many objects at the same time like FLAMES and VIMOS and a few, like KMOS, MUSE and SINFONI, can even take spectra over their whole field of view (see Integral Field Spectroscopy).Īt the La Silla Observatory, the instruments installed at the New Technology Telescope (NTT), EFOSC2 (and its predecessor EMMI) and SOFI are also spectrographs. Only that light is sent to the spectrograph (not shown here), and produce a spectrum of that slit. Most spectrographs select the light to be split using a slit, which can be long or very short, or even just a small hole. They cover different ranges of wavelength (from the near-ultraviolet to the mid-infrared) and offer different spectral resolutions (the higher the spectral resolution, the stronger the dispersion of the light, and the smaller the details of the spectrum that can be detected). Most of the telescopes at ESO’s observatories have spectrographs or have a spectroscopic mode. Spectra also contain information on the magnetic field present in the object, the composition of the matter and much more. This effect is used to discover extrasolar planets, and a similar effect allows astronomers to measure the distances to galaxies. Spectra can also tell us about motion: by using the Doppler effect, the speed of a star or a galaxy with respect to the Earth can be measured. The spectrum of a star or any astronomical object not only reveals the presence of certain chemical elements, but also informs about the prevailing physical conditions, such as temperature and density. The spectra are recorded on a CCD detector and finally saved in computer files for further processing and analysis. Instead of a simple rainbow, the output is a spectrum in which the light is much more dispersed than in a rainbow. Spectrographs are fundamental pieces of astronomical instrumentation and they are far more sophisticated than a prism. The energy that is absorbed by the gas is then re-emitted in all directions, also at the specific colours characteristic of the elements present in the gas, producing bright lines at certain wavelengths this is known as an emission spectrum. In the same way, as light from a star goes through the gas of a nebula - or even just the atmosphere of the star - specific colours (or wavelengths) are absorbed by the elements contained in the gas, producing dark lines over the continuum. When white light goes through a prism, it forms a rainbow, its spectrum. A star emits light across the spectrum - a continuum.
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