Though early twentieth-century astronomers hypothesized that the interstellar medium was entirely devoid of matter, subsequent spectroscopic analyses revealed a sparse distribution of gas and dust. Specifically, the detection of interstellar absorption lines demonstrated that cold sodium and calcium atoms were absorbing starlight, thereby confirming the existence of diffuse matter between stellar bodies. While these gaseous elements are widely dispersed, their presence is not uniform; rather, they accumulate in discrete clouds that attenuate light from background stars. This attenuation, long mistaken for an absence of stars in certain regions of the sky, actually indicates areas of higher density where interstellar dust scatters shorter wavelengths of light, leaving only the longer, redder wavelengths to pass through to Earth.
Based on the passage, the attenuation of starlight in certain regions of the sky is indicative of which of the following?
- regions with greater concentrations of dust that selectively block shorter light wavelengthsAnswer
- Bzones where a total absence of stellar bodies prevents any light from passing through
- Careas where cold sodium and calcium atoms accumulate to scatter red wavelengths of light
- Dregions where the scattering of longer wavelengths of light makes background stars appear blue