What defines sunrise?

Master the Navigation, Seamanship, and Shiphandling (NSS) – Officer of the Deck (OOD) Phase 2 Exam with engaging flashcards and multiple choice questions, complete with hints and explanations. Prepare comprehensively for your test!

Multiple Choice

What defines sunrise?

Sunrise is defined by the moment the upper edge of the Sun’s disk first becomes visible as it rises above the horizon. Because the Sun is not a point but a disk, you don’t see it all at once; the top limb appears first while the rest of the disk is still below the line of sight. At that instant the Sun’s center is about one solar radius (roughly 16 arcminutes) below the horizon, so the event is a consistent, observable reference for dawn. Atmospheric refraction can shift the apparent position slightly, but the standard reference remains the upper limb crossing the horizon. The other descriptions don’t match this observable moment: the Sun’s center being several degrees below the horizon is far from visible; the lower limb crossing horizon would occur later in the rise; and the entire Sun above the horizon occurs even later, after the Sun has fully risen.

Sunrise is defined by the moment the upper edge of the Sun’s disk first becomes visible as it rises above the horizon. Because the Sun is not a point but a disk, you don’t see it all at once; the top limb appears first while the rest of the disk is still below the line of sight. At that instant the Sun’s center is about one solar radius (roughly 16 arcminutes) below the horizon, so the event is a consistent, observable reference for dawn. Atmospheric refraction can shift the apparent position slightly, but the standard reference remains the upper limb crossing the horizon.

The other descriptions don’t match this observable moment: the Sun’s center being several degrees below the horizon is far from visible; the lower limb crossing horizon would occur later in the rise; and the entire Sun above the horizon occurs even later, after the Sun has fully risen.

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