Final answer:
When an observer views the emission of a star unobstructed, they see the star's original color and brightness. However, when the emission is obstructed by a cloud of hydrogen gas, the color shifts toward red for the obstructed observer, the brightness decreases, and the spectrum becomes more continuous.
Step-by-step explanation:
When an observer views a star's emission unobstructed, they will see the star's original color and brightness. However, when an observer views the emission while obstructed by a cloud of hydrogen gas, there are several differences in their observations.
- The color shifts toward red for the obstructed observer. This occurs because the hydrogen gas absorbs certain colors of light, particularly the shorter wavelengths (such as blue and violet), leaving behind the longer wavelengths (such as red). As a result, the star appears more red to the obstructed observer.
- The brightness decreases for the obstructed observer. The hydrogen gas scatters and absorbs some of the star's light, reducing the amount of light that reaches the observer. This leads to a decrease in the overall brightness of the star when observed through the cloud of gas.
- The spectrum becomes continuous for the obstructed observer. When the star's light passes through the cloud of gas, the absorption lines in the spectrum, which are characteristic patterns of missing wavelengths, are filled into some extent. The scattered and reemitted light from the gas more evenly fills in the absorption lines, making the spectrum appear more continuous to the obstructed observer.