Solar Radiation and Earth's Seasons
Introduced| English |
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| solar radiation/ˈsəʊlə ˌreɪdɪˈeɪʃn/ |
Why the year has seasons
- Summer is warm, winter is cold — but why?
- It is not because Earth moves closer to the Sun.
- The real reason is that Earth is tilted.
- That tilt changes how sunlight strikes each hemisphere through the year.
A tilted planet
- Solar radiation 太阳辐射 is the energy Earth receives from the Sun.
- Earth's axis is tilted about 23.5 degrees as it orbits.
- The axis keeps pointing the same way all year.
- So different parts of Earth face the Sun most directly at different times.
What causes Earth's seasons?
The tilt of Earth's axis, not its distance from the Sun, causes the seasons.
Direct rays mean summer
- When a hemisphere tilts toward the Sun, sunlight hits it directly.
- Direct rays are concentrated and the days are long — this is summer.
- When it tilts away, sunlight arrives at a slant and days are short — winter.
- The angle of the Sun's rays, not the distance, sets the season.
Why we have seasons
Step through Earth's tilt and orbit - the tilt, not the distance, gives us the seasons.
It is summer in a hemisphere when that hemisphere…
A hemisphere tilted toward the Sun gets direct, concentrated rays and long days — summer.
Earth's axis is tilted at about ____ point five degrees.
Earth's axial tilt is about 23.5 degrees, and it stays pointed the same way all year.
Opposite hemispheres
- The two hemispheres always tilt opposite ways.
- So when the north has summer, the south has winter, and vice versa.
- Twice a year, at the equinoxes, both get equal day and night.
- The cycle repeats every year as Earth completes its orbit.
When it is summer in the north, it is winter in the south.
The two hemispheres tilt opposite ways, so they always have opposite seasons.
Select all true statements about seasons.
Distance barely changes; the tilt causes the seasons. The other three are correct.
Seasons are not caused by Earth's distance from the Sun. Earth is actually slightly closer to the Sun during northern winter. It is the tilt that matters: a hemisphere tilted toward the Sun gets direct rays and summer, no matter the tiny change in distance.
June around the world:
- In June the northern hemisphere tilts toward the Sun — direct rays, long days, summer.
- At the same moment the southern hemisphere tilts away — slanted rays, short days, winter.
- Same Sun, same distance, opposite seasons — all because of the tilt.
Earth's seasons are caused by its 23.5-degree tilt, not its distance from the Sun. A hemisphere tilted toward the Sun receives direct solar radiation and long days (summer); tilted away, it gets slanted rays and short days (winter). The two hemispheres always have opposite seasons.