Seasons: Why Tilt Matters

Axial tilt causes seasons—not distance from the Sun

Station Card (PDF)
Date
March 21
Season (North)
Spring
Season (South)
Fall
Day Length
12h 0m
Sun Altitude
50.0°
Earth-Sun Distance
0.997 AU
Orbital View
Dashed circle = 1 AU reference. Earth’s distance varies slightly (elliptical orbit), and we exaggerate that change so it’s visible.
Sun Aphelion (Jul) Perihelion (Jan) Polaris Earth March June September December
Globe View
Sunlight N S 40°N Arctic Tropic of Cancer Equator Tropic of Capricorn Antarctic
Date (Day of Year) 80
Jan 1 Apr 1 Jul 1 Oct 1 Dec 31
Season Presets
Axial Tilt 23.5°
0° 90°
Observer Latitude 40°N
90°S Equator 90°N
Animation
Display Overlays
Key misconception addressed: "Many people think seasons happen because Earth is closer to the Sun in summer."

This is wrong! Earth is actually closest to the Sun in January (Northern winter). If distance caused seasons, both hemispheres would have summer simultaneously. Instead, axial tilt means one hemisphere gets more direct sunlight while the other gets less—creating opposite seasons.
Model note: Not to scale: the orbit eccentricity (distance changes) is exaggerated for visibility. We use a simplified Sun-declination model (good to ~1°), so equinox/solstice timing is approximate.