Final answer:
The most difficult wavelength range for obtaining information about the central region of the Milky Way is the visible light range due to the obscuring effects of interstellar dust, which is surmounted by utilizing longer wavelengths like radio and infrared light.
Step-by-step explanation:
Observing the central region of the Milky Way Galaxy presents challenges due to the obscuring effects of interstellar dust, which blocks shorter wavelengths of light, such as those in the visible range. Astronomers overcome this by using long-wavelength radiation, like radio waves and infrared light. The 21-cm line from cool hydrogen and infrared emissions allow astronomers to penetrate the 'smog' and undertake a clearer study of our galaxy's structure, despite us being embedded within it, similar to how difficult it is to map a city from within.
It is most difficult to obtain information using wavelengths that are easily absorbed or scattered by interstellar dust, such as the visible light range. In contrast, radio waves at 21-cm wavelength and infrared emissions at longer wavelengths, for example, 2 microns (2000 nanometers), can pass through the dust much more efficiently, allowing astronomers to study distant parts of the Galaxy and achieve a better understanding of its structure.