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In celestial navigation this means the visible planets Venus, Mars, Jupiter, and Saturn. Mercury is also visible to the naked eye at times, but always too low to be used for sights. Mercury data are not given in the Nautical Almanac, but are available in StarPilot calculators and software. Only Venus and Jupiter have special significance to celestial navigation. Because of their extreme brightness their sights can be taken during the brightest part of twilight with a daylight horizon, which makes them accurate sights that are easy to do. Every 16 years or so, Mars becomes unusually bright (even brighter than Jupiter) and then enters the Venus-Jupiter category of special value.

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