Nautical Twilight

Did you know…

Sunrise is defined as when the sun appears above the horizon and sunset is when the sun disappears below the horizon.

This is important to boaters because of regulations when boat lights are to be used and personal watercraft are to be operated.

Boaters should not confuse sunrise or sunset with civil twilight when the center of the sun is 6 degrees below the horizon and outdoor activities can take place without the need for additional artificial light.

Besides civil twilight, there is also nautical twilight and astronomical twilight.

The period of nautical twilight is when the center of the sun is 12 degrees below the horizon. The outline of objects can be seen at its beginning in the morning or at the end at night and the horizon is indistinct.

The period of astronomical twilight is when the center of the sun is 18 degrees below the horizon. At the beginning of the period in the morning or its end in the evening, the sunlight does not illuminate any portion of the sky and faint stars can be seen.

Make sure to visit the Ultimate Guide to Boating at Grand Lake to find handy links to GRDA and state boating rules and regulations on Grand Lake.

Are you interested in joining a boating club on Grand Lake to have fun, plus the opportunity to take courses online or in the classroom to improve your boating skills and knowledge? 

Visit online or, on Facebook: America’s boating club-grand lake for more information.

Boating Safety - Did You Know

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