The small rockets you are referring to are most likely sounding rockets or rocket-powered vehicles used for scientific research or educational purposes. These rockets are typically launched into the atmosphere to gather data or conduct experiments, and they often leave a long trail or plume behind them as they ascend.
Sounding rockets are designed to reach suborbital altitudes, which means they don't achieve the velocity required to enter orbit around the Earth. They are primarily used for atmospheric and astronomical research, allowing scientists to study various phenomena such as atmospheric conditions, microgravity, radiation, or the behavior of materials in space-like environments.
The trails or plumes left behind by sounding rockets are typically composed of water vapor, exhaust gases, and other byproducts of the rocket's propulsion system. The exact appearance of the trail can vary depending on factors such as the type of propellant used, atmospheric conditions, and the angle at which the rocket is launched.
These rocket launches are often conducted from specialized facilities or launch sites, and they are typically announced in advance to ensure the public is aware of the activity and to prevent any unnecessary concerns or confusion.