Short answers, pulled from the story.
The first raindrop to ever fall on Earth began as a microscopic speck of dust, salt, or ice floating in the atmosphere. This particle serves as a condensation nucleus for water vapor to cling to and transform into a visible cloud. Without these invisible seeds, the water vapor in the air would remain suspended indefinitely.
A falling raindrop is never shaped like a teardrop as air resistance flattens its bottom. As a droplet grows larger, it takes on the appearance of a hamburger bun or, in extreme cases, a parachute. The largest raindrops ever recorded on Earth were measured over Brazil and the Marshall Islands in 2004, reaching diameters of 8.8 millimeters before air resistance caused them to fragment into smaller pieces.
Human activity creates the urban heat island effect, which increases the likelihood of rain by 22% on Saturdays compared to Mondays on the Eastern Seaboard of the United States. Rainfall rates downwind of cities can increase by as much as 116%, with some cities inducing a total precipitation increase of 51%. This influence extends globally, making eastern North America wetter while drying out the tropics.
The phrase acid rain was first coined by Scottish chemist Robert August Smith in 1852. Rain becomes acidic primarily due to the presence of two strong acids, sulfuric acid and nitric acid, which are derived from both natural sources and human activity. Local thunderstorms can even reach a pH as low as 2.0, making them highly corrosive.
Cherrapunji, situated on the southern slopes of the Eastern Himalaya in Shillong, India, holds the title of the confirmed wettest place on Earth. It has an average annual rainfall of 11,872 millimeters and recorded the highest rainfall in a single year there of 26,461 millimeters in 1861. Nearby, Mawsynram, Meghalaya, India, averages 11,871 millimeters of rain per year.
The phenomenon is known as virga, also called fallstreaks or precipitation trails. It is common in hot and arid climates but has been recorded in the Arctic and Antarctica. It is even known to occur on planets beyond Earth, including Mars and Venus, where the atmospheric conditions allow for such optical phenomena.