Passage Summary: Since all stars in a far-off galaxy are about the same distance away, we can assume that if one looks brighter than another, it really is brighter, allowing us to study their characteristics.

Conclusion: We can determine the relationship between a star's actual brightness and its other traits by observing stars within the same distant galaxy.

Reasoning: Because the stars in a single distant galaxy are all roughly the same distance from Earth, any difference in how bright they appear must be due to their actual burning brightness.

Analysis: The argument relies on the assumption that distance is the only factor that could interfere with how bright a star looks to us. However, space is not empty; things like interstellar dust or gas clouds could block the light of some stars more than others, even within the same galaxy. The 'Gap' here is the assumption that no other external factors are distorting the apparent brightness. Look for an answer that confirms that distance is indeed the only significant variable affecting the light we receive from these stars.