Final answer:
A light curve represents the brightness of a star as it is occulted by a planet. Key points on the curve indicate the beginning of coverage, total coverage, emergence, and full visibility of the star.
Step-by-step explanation:
The change in brightness of a star during an occultation by a planet can be described using a light curve, which shows the star's brightness as a function of time. The key moments on the light curve correspond to different phases of the transit of a planet across the star:
- C. Star is beginning to be covered: This is the point where the planet starts transiting across the star, causing a gradual decrease in brightness (first contact).
- A. Star is totally covered: At this point, the transit is at its maximum, and the planet fully covers the star (second contact), resulting in a significant drop in brightness.
- D. Star is emerging: This is when the planet moves away from being directly in front of the star, and the star's brightness begins to return to normal (third contact).
- B. Star is fully visible: The transit event has concluded, and the star's brightness is back to its original state (last contact).