The phenomenon you witnessed, a green light in the sky that was moving and then disappeared, could potentially be attributed to a variety of natural or man-made causes. One possibility is that you observed a type of atmospheric phenomenon known as a green aurora. Auroras occur when charged particles from the Sun collide with atoms and molecules in the Earth's atmosphere, resulting in the emission of light. Green auroras are commonly seen in regions closer to the Earth's poles and are caused by the interaction of solar particles with oxygen in the atmosphere.
Another potential explanation could be a sighting of a meteor or a fireball. Meteors are small particles from space that enter the Earth's atmosphere, and as they burn up due to the friction with the air, they produce a streak of light known as a meteor or shooting star. Occasionally, larger meteors can produce very bright and colorful displays, including greenish hues.
Additionally, it's worth considering the possibility of man-made sources such as fireworks or other pyrotechnic displays. These can produce various colored lights and are often used during celebrations or events.
To determine the exact cause of the green light you observed, additional information and investigation would be necessary. It's important to note that without more specific details, it is challenging to provide a definitive explanation. If you are curious about the event you witnessed, you may want to consult local astronomical societies or organizations who could potentially provide more insights based on your specific location and time of observation.