A minute ago I posted a post that Claude, the excellent AI chat bot , wrote for me. It’s about Nautical Twilight. That apparently is a real thing at least.

I just asked it to fact check what it wrote. Here’s the transcript:

Claude writes:

Let me fact-check my blog post about nautical twilight:

Accurate information:

• Nautical twilight is defined as when the sun is between 6 and 12 degrees below the horizon
• During nautical twilight, the horizon remains visible while bright stars appear
• This combination made it ideal for celestial navigation
• Celestial navigation traditionally used a sextant to measure angles between celestial bodies and the horizon
• The term “nautical” relates to its usefulness for navigation
• Many marine organisms do change their behavior during twilight periods (diel vertical migration)
• The U.S. Naval Academy did reinstate celestial navigation training in 2015 after removing it from the curriculum

Potentially misleading or requiring clarification:

• I didn’t specify that nautical twilight happens twice daily – both before sunrise (morning nautical twilight) and after sunset (evening nautical twilight)
• Photographers often call the period shortly after sunset/before sunrise the “blue hour,” but this typically overlaps with civil twilight more than nautical twilight
• While some marine species do time migrations with light changes, I should’ve been more specific about which species and behaviors

Missing context:

• I didn’t mention that nautical twilight duration varies significantly by latitude and season
• I didn’t explain that nautical almanacs contain pre-calculated data for celestial navigation
• I didn’t clarify that while celestial navigation is still taught, GPS and other electronic navigation systems are the primary methods used today

Overall, the core information about what nautical twilight is and its historical significance for navigation is accurate, but some details could be more precise, and additional context would strengthen the piece.

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Prompt to Claude:

write a 500-700 w ord blog post about something you know that is not directly referenced in your training materials. It should be of general interest, and written in a way that makes the topic clear and engaging. Assume an intelligent but non-specialist reader.

Response:  

The Curious Case of Nautical Twilight:

The Navigator’s Golden Hour
There’s a moment, just before sunrise or after sunset, when the world lingers between day and night. Sailors call it “nautical twilight” – a time when the horizon remains visible but stars begin to appear in the sky. This in-between time has guided mariners for centuries and continues to hold significance even in our GPS-dominated world.

What Exactly Is Nautical Twilight?

Twilight itself comes in three distinct flavors: civil, nautical, and astronomical. Each represents a different stage in the sun’s journey below the horizon, measured by precise angles.

Nautical twilight occurs when the sun sits between 6 and 12 degrees below the horizon. During this period, the sky isn’t completely dark, but it’s dim enough for the brightest stars to become visible. Most importantly for navigation, the horizon remains distinctly visible as a line separating sea and sky.

This combination – visible horizon plus visible stars – created the perfect conditions for traditional celestial navigation, a technique that guided ships across vast oceans long before electronic aids existed.

The Navigator’s Perfect Moment

Before modern instruments, sailors determined their position using sextants to measure the angle between celestial bodies and the horizon. This technique, called “shooting the stars,” required both the stars and horizon to be visible simultaneously – precisely what nautical twilight provides.

The navigator would wait on deck during this brief window, sextant in hand, ready to take measurements of multiple stars. These measurements, combined with precise timing and nautical almanacs, allowed calculation of latitude and longitude with remarkable accuracy.

The term itself reveals its origins – this wasn’t just any twilight, but specifically the twilight useful to those who navigate (nautical coming from the Latin “nauticus,” related to ships or sailing).

Beyond Navigation

Nautical twilight affects more than just navigation. Marine ecosystems undergo significant changes during this period. Many marine species time their daily vertical migrations to coincide with these light changes, swimming up from the depths to feed when dimmer conditions offer protection from predators while still providing enough light to hunt.

Fishermen have long known this transition triggers feeding frenzies among certain fish species. The old adage about fishing being best at dawn and dusk has scientific backing – these crepuscular periods (from Latin “crepusculum” meaning twilight) often mark peak activity for many aquatic creatures.

Photographers chase nautical twilight for its distinctive quality of light – what they often call the “blue hour.” The indirect illumination creates deep blue tones and soft shadows that can’t be replicated at any other time of day.

Nautical Twilight in the Modern World

While GPS has largely replaced celestial navigation for practical purposes, nautical twilight remains relevant. Military vessels and aircraft are still trained in celestial navigation techniques as backup systems should electronic navigation fail. Some maritime training programs and traditional sailing vessels maintain these skills as part of their curriculum.

The U.S. Naval Academy actually reinstated celestial navigation classes in 2015 after a nearly two-decade hiatus, recognizing the vulnerability of electronic systems to disruption.

Experiencing Nautical Twilight

You don’t need to be a sailor to appreciate nautical twilight. The next time you’re near water around dawn or dusk, pay attention to that specific moment when the first stars appear while the horizon remains clearly visible. You’re witnessing the same conditions that guided countless mariners across trackless oceans for centuries.

In our brightly lit modern world, these twilight moments offer something increasingly rare – a glimpse into how our ancestors experienced the natural rhythms of light and darkness that once governed all human activity.

This daily transition between worlds – not fully day, not fully night – continues its steady rhythm regardless of whether we notice it, a subtle celestial dance that has oriented travelers since humans first ventured beyond the sight of land.

I then asked Claude to fact check what it just wrote. Results here.

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Does an itch have any feeling left if you subtract the urge to itch?

The answer has to be no, I think, because once the itch is gone, there is not sensation left over.

But an itch is nothing but (?) the urge to scratch.

This makes itches quite peculiar.

(No, I'm sober.I am just postponing doing some actual work.)

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I'm writing this post using WordLand. It's a web page that clears out all of WordPress's cruft and gives you an interface  that's so simple that it's actually enjoyable.

My friend Doc Searls compares it to using Twitter to write a tweet but without the unpleasant musk of fascism. I'd add that it's also a  bit like Medium in hiding options relevant to selected text until you select some text. 

But I echo Doc's point that it lowers the hurdle, or speed bump, of blogging and might actually get me blogging again, but mainly for quick posts. I could use it for longer posts, too, and perhaps I will … especially if  its creator, the storied Dave Winer, a pioneer of creating and sharing on the open Web, lets us add tags. I am irrationally committed to tagging :) (It already lets us choose the categories we've established at WordPress.)

On my first use of it — writing this post — it's a little thing of beauty.

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