Why are rocket launches often timed to a narrow launch window?

A launch window is the period when a rocket can safely and efficiently leave Earth for its destination. For orbital missions, the target orbit must line up with Earth’s rotation, the vehicle’s path, and mission constraints such as lighting, communications, and weather. For trips to the Moon or other planets, the window may be even narrower because the destination is moving too. Apollo and interplanetary missions both depended on precise timing, where missing the window could mean waiting hours, days, or months for the next opportunity.