Week 04 · Seasons

Thursday

Reading the day-length table

// A tilted axis that always points the same way

⏱ about 20 min

Thursday: Reading the Day-Length Table

Raven pins a table to the Sky Deck wall. "From the United States Naval Observatory. Longest and shortest days by latitude."

Rocket reads the first row. "At 25 degrees north, the longest day is 13 hours 42 minutes. The shortest is 10 hours 35 minutes."

"What do you notice as you go down the rows?" Raven asks.

"Farther north, the longest day gets longer," Rocket says. "At 60 degrees it is almost 19 hours. And the shortest day is under 6 hours."

Nova hovers over the table. "Why would farther north mean bigger swings?"

Rocket grabs the tilted ball. "The far north leans all the way into the Sun in June, and all the way out in December."

Nova hums. "Now read every row."

The table from the Naval Observatory

The United States Naval Observatory publishes the longest day and shortest day for several latitudes north of the equator.

Latitude is how many degrees you are north of the equator. The equator is 0 degrees and the North Pole is 90.

Read every row before you answer the questions. Then compare the swing between summer and winter at each latitude.

Latitude	Longest day	Shortest day
25 degrees north	13 h 42 min	10 h 35 min
35 degrees north	14 h 31 min	9 h 48 min
40 degrees north	15 h 02 min	9 h 20 min
45 degrees north	15 h 38 min	8 h 46 min
50 degrees north	16 h 23 min	8 h 04 min
60 degrees north	18 h 53 min	5 h 52 min

The pattern is clear. The farther north you live, the longer your longest day and the shorter your shortest day.

Near the equator, OpenStax says, every day of the year has about 12 hours of sunshine and 12 hours of night.

At the poles it is extreme: about 6 months of sunshine followed by 6 months of darkness each year.

The Naval Observatory also notes that the longest day is a little longer than the longest night. Sunrise and sunset are measured from the Sun's top edge.

USE THE TABLE

Read the question.
Tap your answer.

Which latitude in the table has the longest longest day?

At 40 degrees north, about how long is the shortest day?

What happens to the swing between longest and shortest day as you go north?

Near the equator, every day has about ____ hours of sunshine.

At 60 degrees north the shortest day is less than ____ hours long.

Statement	True or false?
At 25 degrees north the longest day is under 14 hours.	?
At 50 degrees north the shortest day is longer than 9 hours.	?
The poles have about 6 months of sunshine and 6 months of darkness.	?
Day length changes the same amount at every latitude.	?

WHY THIS EXERCISEThe tilt changes day length most where the lean toward or away from the Sun is greatest.

SHORTEST DAY, FROM LONGEST TO SHORTEST

Tap a card.
Then tap its spot.

1Longest

2Second

3Third

4Shortest

Try it

Ask a grown-up roughly what latitude your home is. Find the nearest row in the table.
Write your longest and shortest day from that row. Does your Sky Log sunset trend agree with the season you are in?

Try this

Cover the Shortest day column and test yourself on three rows. Record how many you got right.
Subtract shortest from longest for the 25 and 60 degree rows. Which swing is bigger?

Draw a bar chart with a bar for the longest day at 25, 40 and 60 degrees north. Add a shorter bar for each shortest day.

Which row of the table is closest to your home? Write what it predicts about your summer and winter days.Moon log check: today's date and the Moon's shape, or "clouds".Why do you think the far north has such long summer days? Use the tilted ball to explain in two sentences.

Careful reading. Tomorrow you connect the seasons to everyday life, review the week and look ahead.

Grown-up checked my answers

← Wednesday Friday →