Astronomical observations (starlight): The light that we receive from very distant stars is affected primarily by what? Consider both near-Earth and interstellar influences on incoming starlight. Choose the correct combination.

Given data

• Asks what modifies the light of distant stars before it reaches observers.

Concept/Approach
Interstellar dust causes extinction and reddening of starlight over vast distances. Near Earth, the atmosphere introduces seeing effects (scintillation/twinkling), absorption and scattering (especially at shorter wavelengths). Thus, both significantly affect the observed light.

Final Answer
Both (a) and (b)