You are heading due east (090) and observe a vessel's red sidelight on your port beam. The vessel may be heading _____________.

When you are heading due east (090 degrees) and observe a vessel's red sidelight on your port beam, it indicates the position of that vessel relative to your boat. The red sidelight is used to indicate the port side (left side when facing forward) of a vessel.

For a vessel's red sidelight to be visible on your port beam, that vessel must be approaching from a direction where its port side is facing towards you. If your heading is 090 degrees (due east) and you see the red light on your left (port side), the other vessel must be positioned at an angle that allows its port side to face you.

In this scenario, if you deduce that the other vessel is to your northeast, it would be traveling south-southeast (135 degrees), with its left side facing eastward where you are positioned. The only viable option that corresponds with this information is the vessel heading southwest (225 degrees), which places it within the view of your port side. This understanding allows you to interpret navigational lights and positions effectively, which is crucial for safe boating practices.

By recognizing how navigation lights work and their corresponding angles, one can make informed decisions about other vessels' movements and ensure safer navigation