Final answer:
Geosynchronous satellites can remain overhead in Singapore due to its proximity to the equator, but not over cities far from the equator like San Francisco, Chicago, or New York City. These satellites are placed in an orbit that keeps them fixed relative to a point on Earth, making them ideal for communication and weather observation.
Step-by-step explanation:
A geosynchronous Earth satellite is one that has an orbital period of precisely 1 day, meaning it remains fixed above a single point on the Earth's equator. The satellite can remain directly overhead Singapore because Singapore is near the equator, where an ideal geosynchronous orbit lies. However, cities like San Francisco, Chicago, or New York City cannot have a geosynchronous satellite directly overhead because they are located far from the equator, and the orbital path of such satellites does not align with their latitude.
Geosynchronous satellites are very important for applications requiring a fixed position relative to the Earth, such as for communication and weather observation. They require a considerable amount of energy to be placed into their specific orbit and once there, and if high enough to avoid atmospheric drag, they can remain in orbit indefinitely. All fixed satellite dishes on the ground, such as those for TV reception, are aimed at these satellites because they offer stable reception from a constant location in the sky.