Explanation:
waterfalls are temporary features of rivers because stream erosion is greatest at waterfalls and rapids. The water that falls at the base of the waterfall erodes rock there, leaving the rock at the tops of the waterfalls to overhang. Overall, undermining causes waterfalls to recede farther upstream.
Watching the light level dip as a planet moves across its star at a regular interval.
Analyzing Spectra from the surface of the star in which matter may have been accreted onto it.. i. e. Carbon or heavier elements like tin.
The answer is a Lunar eclipse