You see a vessel's green sidelight bearing due east from you. The vessel might be heading _____________.

When observing a vessel's green sidelight bearing due east, it indicates the vessel’s starboard (right) side is facing that direction. In the context of maritime navigation and the positioning of lights on vessels, the green sidelight is visible from the starboard side, while the red sidelight is visible from the port (left) side.

If you see the green light directly to your east, it means the vessel is likely turning towards a direction where its starboard side is facing you. The possible headings for this scenario would typically be either heading towards the east or a direction where you would also be able to see the starboard side, such as northeast or southeast.

However, the correct answer points more specifically to the northwest heading, as from your perspective, if the green light is directly east, the vessel must be oriented such that it is moving towards you from a direction along the arc of the circular horizon you share with it.

Thus, the vessel might indeed be heading northwest, because although you see the green light now, as it moves further along, you would be observing its path moving across your direct line of sight from the east moving towards the northwest. In maritime navigation, this directional understanding is critical for safe navigation practices.