Solar Terminator Map
The solar terminator is the moving boundary dividing Earth's daylight illumination and nighttime darkness. Computed from precise solar declination, the equation of time, and axial obliquity, inspect day/night boundaries across the globe, scrub solar cycles, and explore seasonal solstices and equinoxes.
Subsolar Point & Zenith
The subsolar point is the exact position on Earth's surface where the Sun is perceived directly overhead at the zenith (90° altitude angle). As Earth rotates, this point moves westward at 15 degrees of longitude per hour (roughly 1,670 km/h at the equator).
Equation of Time & Obliquity
Due to Earth's orbital eccentricity (0.0167) and the 23.44° axial tilt (obliquity), apparent solar noon varies from mean clock noon by up to ±16 minutes throughout the year. The solar calculations here model this analemma variation in real time.
Great Circle Night Geometry
Geometrically, the solar terminator is a great circle 90° away from the subsolar point. The dark hemisphere is rendered via spherical polygon coordinates centered on the antipodal point (λ + 180°, -δ), seamlessly projected onto any map coordinate system.