Why we have
seasons.

Earth's real orbit is slightly elliptical, and distance affects incoming sunlight a little. But the opposing seasonal cycles of the hemispheres are driven by tilt. This lesson includes changing distance and inverse-square solar illumination. Earth is closest to the Sun near January, during northern winter; tilt explains the hemispheres’ opposite seasons.

The axis remains tilted 23.4° from orbital north in 3D. A view from the Sun changes direction through the year. At an equinox you see the tilt sideways. At a solstice it points toward or away from you, so its projection can look vertical. Keep the physical tilt fixed; change only the camera.

From Sun · follow orbit keeps the camera on the Sun–Earth line with orbital north up. Pole markers show where the axis crosses the sphere. A far-side pole is hollow because it lies behind the visible surface. The internal dashed axis is a cutaway guide, not a feature visible through Earth.

Earth's axis is tilted 23.4° from the perpendicular to its orbital plane. Its orientation is effectively fixed over one year. We use a rounded 365.25-day year, a fixed Keplerian ellipse with eccentricity 0.0167 and varying orbital speed; the month labels are approximate rather than an astronomical calendar. The Sun is at one focus. From directly above, the true ellipse looks almost circular; oblique viewpoints flatten its projection. Orbital elements are approximate and fixed, rather than a dated ephemeris. The orbital Earth and the large globe share a 3D axis and Sun direction. Apparent tilt varies with the viewing angle; 23.4° is the true angle from the orbital perpendicular.

Daylight uses the geometric centre of the Sun and a level horizon, excluding atmospheric refraction, terrain and twilight. At an exact pole on an equinox, the ideal Sun sits on the horizon, so a normal daylight duration is undefined. The local sky diagram shows noon elevation, not a compass direction or the Sun's full daily path. The globe uses direct solar illumination with cosine falloff and a dark night side; atmospheric scattering, terrain relief, clouds and artificial lights are not simulated.

Not necessarily. Oceans, land and the atmosphere store and move heat, so the hottest and coldest periods often lag the solstices. Clouds, altitude and local climate also matter. Near the equator, wet and dry seasons may be more useful descriptions than four temperature seasons.

A solar day measures the return of the Sun to the same meridian; a sidereal rotation is a full turn relative to the stars. Because Earth travels around the Sun in the same direction as it spins, it makes approximately one extra full rotation per orbit. Our shared clock therefore links 365.25 mean solar days to 366.25 full turns in an ideal year.

The initial geographic orientation and clock zero are illustrative, not an exact UTC ephemeris. The model clock counts time from an ideal March equinox. Surface spin never resets when the year loops.

NASA: solar and sidereal rotation

Solar declination is calculated from orbital position and axial tilt. Day length follows from the portion of a latitude's daily circle above the geometric horizon. Noon elevation is 90° minus the absolute difference between latitude and solar declination.

NASA: Earth's energy budget and seasons · NASA: Earth orbital elements · NOAA: solar calculation assumptions