Articles
Atmospheric Science
Civil, Nautical, & Astronomical Twilight: What Is the Difference?
Understand the three official stages of twilight defined by solar depression angles (-6°, -12°, and -18°). Learn how scientists, sailors, and stargazers use each phase.
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Solar Geometry
How Sunrise and Sunset Are Defined (Refraction, Zenith & the Solar Disk)
Official sunrise and sunset use a 90.833° zenith that includes refraction and the Sun’s radius. Here’s what that means for the times you see.
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Solar Geometry
Solar Noon & True Solar Time: Why Your Clock Isn't Always Accurate
Learn what Solar Noon really means, how to measure true solar transit time, and why civil time zone clocks rarely align with the Sun zenith.
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Celestial Mechanics
How Sunrise Time Changes Throughout the Year
Explore the celestial mechanics behind seasonal sunrise variations, axial tilt, and why the earliest sunrise does not occur on the solstice.
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