Earth’s axis leans about 23.4° from straight up-and-down to its orbit, and that lean keeps pointing the same way in space all year. The hemisphere tipped toward the Sun gets a higher Sun, more direct light, and a longer day. Pair with the solar map (where Earth sits among the planets) and the Annual Dial (the year as a circle of days).
Educational schematic — not a precision ephemeris and not a weather forecast. The orbit oval is exaggerated (Earth’s real path is almost a circle), and the Earth disks are enlarged so the axis is visible. Solstice and equinox buttons use a non-leap classroom calendar: about March 20, June 21, September 22, and December 21. Real dates drift by a day.
Interactive · Orbit and tilt
Move the day · the axis stays parallel · it does not flip
Jun 21
Interactive · Day length by latitude
Classroom hour angle · approximate
~14.5 h
long day in the north
June 21 · 37° N
37° N
Northern latitudes get the long day. Toward the Arctic Circle the geometric Sun stays up almost all day; toward the Antarctic Circle it barely rises.
Daylight vs latitude · declination about 23.4° north
Approximate classroom math, not a sunrise almanac. It uses the declination already drawn above and the standard hour-angle relation: cosine of the hour angle equals minus tan(latitude) times tan(declination), and day length is about twice that angle divided by 15. When the cosine falls outside −1 to 1, the label switches to polar day or polar night. Refraction, elevation, and the equation of time are ignored. The slider starts at 37° N — Campbell / South Bay, the Local sky default — and this day is the one on the Annual Dial.
Literacy · words for the year
Axial tilt (obliquity)
Earth’s spin axis leans about 23.4° from perpendicular to its orbit. NASA names that tilt as the cause of the yearly seasons. The lean keeps pointing the same direction in space while Earth goes around the Sun — it does not flip each season.
Solstice
The two dates when a pole leans most toward or away from the Sun — about June 21 and December 21 on this classroom calendar. One hemisphere has its longest day; the other has its shortest. The Sun’s midday height stops climbing or falling and turns back.
Equinox
The two dates when the axis leans sideways to the Sun–Earth line — about March 20 and September 22 here. Day and night are roughly equal in both hemispheres, and the most direct sunlight falls near the equator.
Perihelion / aphelion
Closest and farthest points in the orbit. Perihelion falls in early January (Northern winter); aphelion falls in early July (Northern summer). The mile gap NASA publishes is real, and it is not what drives the seasons.
Day length / hour angle
How long the geometric Sun stays above a flat horizon. Latitude φ and declination δ set the hour angle by cos ω = −tan φ tan δ; daylight is about 2ω/15 hours when ω is in degrees. If that cosine falls outside −1 to 1, the latitude is in polar day or polar night. Classroom approximation — refraction makes a real sunrise a few minutes earlier.
Sources · public NASA education
Cited, not invented
NASA Science — Earth facts — axis tilted 23.4° to the orbit; that tilt causes the seasons; six months later the hemispheres reverse; at the start of spring and fall both receive roughly equal heat.
NASA Space Place — What causes the seasons? — the axis keeps pointing the same way; perihelion 91,400,000 miles in January; aphelion 94,500,000 miles in July; Northern winter happens at the closer distance.
NOAA Global Monitoring Laboratory — Solar calculation details — sunrise and sunset calculations based on Jean Meeus, Astronomical Algorithms, with about 0.833° of refraction assumed. NOAA says the results are approximate and not certified for legal use.
Geometric daylight, as in standard spherical-astronomy textbooks: cos ω = −tan φ tan δ, and day length ≈ 2ω/15 hours (ω in degrees). Polar day or polar night when that cosine falls outside −1 to 1. This strip uses that classroom form — no refraction — with the declination sine already on the page.
Figures are teaching toys. A real solstice clock time, a local sunrise, or tomorrow’s weather needs an almanac or a forecast — not this page. Kilometer values are the Space Place mile figures rounded, not a second ephemeris. Earthrise preview: NASA / Bill Anders (public domain).