Raven shines the flashlight straight down at the Sky Deck step. A small bright circle. "What do you notice?"
"Bright and tight," Rocket says. Raven tips the flashlight. The circle stretches into a long dim oval.
"Same light," Rocket says. "Spread out more. So each spot gets less."
Nova hovers above. "That is effect one," she says. "Slanted light is weaker light. What is effect two?"
Rocket checks the Sky Log. "Sunset keeps coming earlier. The Sun is up for fewer hours."
"Steeper and longer in summer," Raven says. "Flatter and shorter in winter."
Nova hums. "Two effects, one tilt."
When your hemisphere leans into the Sun, sunlight hits the ground at a more direct angle. It is more effective at heating.
OpenStax describes a flashlight on a wall. Shine it straight on and you get an intense spot. Tilt it and the spot spreads out.
In June the Sun appears high in the sky for the Northern Hemisphere. Its rays hit more directly and spread out less.
In December the Sun is low. Its rays spread over a much wider area and heat the ground less.
NASA says it the same way: with the Sun higher in the sky, solar heating is greater, producing summer.
The second effect is how long the Sun stays above the horizon. Daylight hours grow in summer and shrink in winter.
Around June 21, the Sun is above the horizon in the United States for about 15 hours.
Around December 21, it is up for about 9 hours. Around March 21 and September 21, day and night are about equal.
So in summer the Sun heats with more direct rays, and it also has more hours each day to do it.
| Statement | True or false? |
|---|---|
| Direct sunlight heats the ground more than slanted sunlight. | ? |
| In summer the Sun is low in the sky at noon. | ? |
| Longer days give the Sun more time to heat the ground. | ? |
| Day and night are about equal around June 21. | ? |
Clear thinking. Tomorrow is Sky Deck Lab: you count the squares a flashlight lights, straight down and at a slant.