Below are the conditions used on a starship and what they mean. Generally speaking on Federation starships there are four alert conditions.

Alert Conditions

Condition Meaning Alert Condition Green is the alert that starships are always in. It signifies that all systems are nominal and there are no threats to the vessel.

Alert Condition Yellow is the potential for a threat to the vessel. Be it from an enemy combatant or natural phenomena. However, it does not indicate a state of emergency, or battle-stations. It quite simply indicates that everyone should be ready for anything.

Alert Condition Red is battle-stations. It indicates a clear and present danger to the vessel and the lives aboard the vessel. Very often when the ship is at red alert off duty crew will be called into service.

On a Thucydides Class Starship alert condition blue indicates that a temporal incursion is imminent. Specifically that something is going to effect the prime universe. Be it someone or something arriving through time or from another universe. This condition activates at the order of the Chief Temporal Mechanics Officer. Crew is to report to battle stations and secure the ship from any effects of the timeline.

Alert Condition Black is unique and used only on a Thucydides Class Starship. It signifies when the ship is going to engage the temporal drive and initiate a temporal incursion. This condition can only be initiated by the Commanding Officer or the Executive Officer and only with the concurrence of the Chief Temporal Mechanics Officer. It alerts the crew the ship will make a jump and prompts them to take all appropriate precautions to secure the ship from potential threats to the Temporal Prime Directive. Once Black Alert is cancelled, Yellow Alert must be initiated.