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Week 04 · Seasons

Friday

Seasons in your life
// A tilted axis that always points the same way
⏱ about 20 min

Friday: Seasons in Your Life

Rocket flips through the Sky Log at the Sky Deck. "Sunset has moved along the fence every week since week 1."

"What do you notice about the direction?" Raven asks. "It keeps sliding the same way," Rocket says. "A little each week."

Nova hovers over the page. "The Sun's path shifts with the seasons," she says. "That is why your mark moves."

"And the hottest day is not the longest day," Raven adds. "July and August are hotter than June 21."

"Why?" Rocket asks. Raven points at the pond at the end of the yard. "It takes time to warm up. So does Earth."

Nova hums. "Patterns in the log, explained by one tilt. Review time."

Why your sunset mark moves

OpenStax says you can watch, from one spot, where the Sun rises or sets relative to a fixed landmark.

Around June 21 the Sun rises north of east and sets north of west. Around December 21 it rises south of east and sets south of west.

In between, the sunset point slides along the horizon a little each week. That is what your Sky Log has been recording.

In spring the sunset moves farther north each week until the June solstice. In autumn it moves south until December.

Why the hottest days come later

The June solstice is the longest day, but it is not the warmest. The hottest months in the Northern Hemisphere are July and August.

OpenStax explains that air and water cover Earth's surface, and these large reservoirs do not heat up at once.

A pond is warmest late in the afternoon, after it has had time to absorb the Sun's heat. Earth works the same way.

The coldest times of winter come a month or more after the December solstice for the same reason.

Next week you meet the force that holds Earth, the Moon and the planets in their orbits: gravity.

DateSunriseSunsetDaylight in the United States
Around June 21north of eastnorth of westabout 15 hours
Around September 21between the June and December pointsbetween the June and December pointsabout 12 hours
Around December 21south of eastsouth of westabout 9 hours
Around March 21between the June and December pointsbetween the June and December pointsabout 12 hours
EXPLAIN IT
  • Read the question.
  • Tap your answer.
Why does your sunset landmark move week to week?
Why are July and August hotter than June 21, the longest day?
Around December 21, where does the Sun set for the United States?
Week reviewTrue or false?
Earth's axis is tilted about 23.5 degrees and points the same way all year.?
The seasons are caused by Earth's changing distance from the Sun.?
Direct sunlight heats the ground more than slanted sunlight.?
The two hemispheres have the same season at the same time.?
Day length swings more at higher latitudes.?
WHY THIS EXERCISEThese five ideas explain the seasons with one tilted axis.
OUR WEEK, IN ORDER
  • ?We learned that Earth is closest to the Sun in January, so distance is not the cause.
  • ?We learned the two effects of the tilt: more direct light and longer days.
  • ?We counted the squares a flashlight lights, straight down and at a slant.
  • ?We read the Naval Observatory table of longest and shortest days.
  • ?We explained the moving sunset mark and why the hottest days come late.
WHY THIS EXERCISEThe week moved from a wrong guess about distance to a model and a table that explain the seasons.
In which month is Earth closest to the Sun? Type the month.
WHY THIS EXERCISEThis fact alone shows that distance is not what makes summer warm.
Try it
Fill a cup with cool water and set it in a sunny window. Touch the outside now and again after an hour.
Write how long it took to feel warmer. Earth's oceans and land warm slowly the same way, never taste the water.
Draw your horizon with the week 1 sunset mark and this week's mark. Add an arrow showing which way it has moved.

Strong week, season scientist. Tomorrow is Sky Night: the family checks the sunset mark and the Moon.

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