What does an asterisk (*) next to an altitude indicate on a chart?

An asterisk (*) next to an altitude on a chart indicates the Minimum Obstacle Clearance Altitude (MOCA). This altitude is important for ensuring safe navigation over obstacles in the vicinity of the route. The MOCA provides the minimum altitude prescribed for obstacle clearance within a particular sector and ensures that aircraft maintain a certain vertical distance above terrain and obstructions.

MOCA is also critical for navigation, as it guarantees that even in areas where navigation aids might not be available, pilots can still clear obstacles by a set margin. This is particularly useful in mountainous terrain or regions with scattered tall obstructions.

Understanding this notation and its implications helps pilots make informed decisions regarding altitude selection for safe flight, especially when flying under instrument conditions. The other options do relate to altitudes in different contexts but do not refer specifically to the designation indicated by the asterisk.