Question

dust obscures visible light from distant stars.
therefore, how can astronomers confidently measure the rotation curve of the milky way?
astronomers use space - based telescopes to directly observe the galaxys rotation.
astronomers measure the motion of dwarf galaxies orbiting the milky way.
astronomers can measure the rotation curve of the milky way using only nearby visible stars.
radio telescopes capture data on the motion of hydrogen gas all through the galaxy.

Explanation:

Dust obscures visible - light from distant stars. Radio waves can penetrate dust. Radio telescopes can detect the motion of hydrogen gas in the Galaxy, which helps in measuring the rotation curve. Space - based telescopes still face issues with dust for direct observation. Measuring dwarf galaxies' motion gives information about the overall mass but not directly the rotation curve in detail. Using only nearby visible stars is not sufficient as it doesn't represent the whole Galaxy.

Answer:

Radio telescopes capture data on the motion of hydrogen gas all through the Galaxy.