<Tr> <Td> Protostar outburst - HOPS 383 (2015). </Td> </Tr> <P> Key elements of star formation are only available by observing in wavelengths other than the optical . The protostellar stage of stellar existence is almost invariably hidden away deep inside dense clouds of gas and dust left over from the GMC . Often, these star - forming cocoons known as Bok globules, can be seen in silhouette against bright emission from surrounding gas . Early stages of a star's life can be seen in infrared light, which penetrates the dust more easily than visible light . Observations from the Wide - field Infrared Survey Explorer (WISE) have thus been especially important for unveiling numerous Galactic protostars and their parent star clusters . Examples of such embedded star clusters are FSR 1184, FSR 1190, Camargo 14, Camargo 74, Majaess 64, and Majaess 98 . </P> <P> The structure of the molecular cloud and the effects of the protostar can be observed in near - IR extinction maps (where the number of stars are counted per unit area and compared to a nearby zero extinction area of sky), continuum dust emission and rotational transitions of CO and other molecules; these last two are observed in the millimeter and submillimeter range . The radiation from the protostar and early star has to be observed in infrared astronomy wavelengths, as the extinction caused by the rest of the cloud in which the star is forming is usually too big to allow us to observe it in the visual part of the spectrum . This presents considerable difficulties as the Earth's atmosphere is almost entirely opaque from 20μm to 850μm, with narrow windows at 200μm and 450μm . Even outside this range, atmospheric subtraction techniques must be used . </P> <P> X-ray observations have proven useful for studying young stars, since X-ray emission from these objects is 100--100,000 times stronger than X-ray emission from main - sequence stars . The earliest detections of X-rays from T Tauri stars were made by the Einstein X-ray Observatory . For low - mass stars X-rays are generated by the heating of the stellar corona through magnetic reconnection, while for high - mass O and early B - type stars X-rays are generated through supersonic shocks in the stellar winds . Photons in the soft X-ray energy range covered by the Chandra X-ray Observatory and XMM Newton may penetrate the interstellar medium with only moderate absorption due to gas, making the X-ray a useful wavelength for seeing the stellar populations within molecular clouds . X-ray emission as evidence of stellar youth makes this band particularly useful for performing censuses of stars in star - forming regions, given that not all young stars have infrared excesses . X-ray observations have provided near - complete censuses of all stellar - mass objects in the Orion Nebula Cluster and Taurus Molecular Cloud . </P>

What primarily makes it difficult to observe the process of star formation
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