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Physical Geography (GE 306)

Books and websites on specific research topics for physical geography, as well as practice quizzes

Answers to Questions in the Earth/Sun Relations and Seasons Tutorial

This page contains the answers to the questions embedded throughout the Tutorial on Earth/Sun Relations and Seasons.

Question 1

1. To which star does the Earth’s axis point? That is, which star is almost directly overhead at the North Pole?

The North Star, or Polaris

Question 2

2. On June 21, the subsolar point is at about 23.5 degrees north. The next day, will the subsolar point be north or south of the Tropic of Cancer?

South. The subsolar point will not move north of the Tropic of Cancer. After the solstice, the Sun’s direct rays will move toward the south (though the southward movement is so slow it is not apparent for a few days; “solstice” means “Sun stands”: the Sun’s rays reach the Tropic, and appear to stop for a while before moving south again). The subsolar point will get to the equator three months later, and to the Tropic of Capricorn about 3 months after that.

Questions 3-5

3. If day length is 24 hours at the North Pole during the June solstice, and 0 hours at the South Pole during the June solstice, what is the day length at the equator on that day?

12 hours. You can get at this in a couple of ways. One, the circle of illumination is a great circle, and so is the equator. Great circles always bisect each other, so if the equator cuts the circle of illumination in half, it must get 12 hours of light and 12 hours of dark. Or, you can just figure that there are 0 hours of daylight at the South Pole and 24 at the North Pole, so since the equator is halfway in between, it must get 12 hours of daylight.

Bonus questions:
4. If the Sun is directly overhead at the Tropic of Cancer (that is, the angle of incidence is 90 degrees), what is the angle of incidence at noon at the equator?

The Sun at noon would be 66.5 degrees above the horizon at the equator. The Sun’s altitude at 23.5 degrees north is 90 degrees (directly overhead). The difference in latitude between the subsolar point (23.5 degrees north) and the equator (0 degrees) is 23.5, and 90-23.5=66.5.

5. If the Sun is directly overhead at the Tropic of Cancer (that is, the angle of incidence is 90 degrees), what is the angle of incidence at noon at the North Pole?

The Sun at noon would be 23.5 degrees above the horizon. The Sun’s altitude at 23.5 degrees north is 90 degrees (directly overhead). The difference in latitude between the subsolar point (23.5 degrees north) and the North Pole (90 degrees north) is 66.5, and 90-66.5=23.5. At the North Pole on the June solstice, the Sun circles around all day 23.5 degrees above the horizon.

Questions 6-8

6. At the December solstice, the Sun is shining directly on the Tropic of Capricorn. The day after the solstice, will the subsolar point be north or south of the Tropic of Capricorn?

North

7. Six months after the December solstice (on, say, June 21), where will the subsolar point be?

At the Tropic of Cancer. This will be the June solstice.

8. Three months after the December solstice (on, say, March 20), where will the subsolar point be?

At the equator. This will be the equinox. For the Northern Hemisphere, it is the spring (vernal) equinox, since the subsolar point is moving north toward the Tropic of Cancer.

Question 9

9. Aphelion takes place on July 4, which is summer for which hemisphere?

The Northern Hemisphere

Summary Questions

At the June Solstice - The date is June 21 or 22

1. The subsolar point is at what latitude?

23.5 degrees north

2. What is this latitude called?

The Tropic of Cancer, the northern boundary of the tropics

3. What is the length of daylight at the equator?

12 hours; day length is always about 12 hours at the equator

4. What is the length of daylight at the North Pole?

24 hours; the Sun does not rise or set at the North Pole on the June solstice, it just circles around, 23.5 degrees above the horizon

5. What is the length of daylight at the South Pole?

0 hours; the South Pole has 24 hours of night on the June solstice, when the Sun does not rise above the horizon

6. On this day, every location south of what Circle is in darkness for 24 hours?

The Antarctic Circle

7. Every location north of what Circle gets 24 hours of daylight?

The Arctic Circle

8. This day is the longest day of the year for which Hemisphere?

The Northern Hemisphere

9. At the equator, what is the Sun’s altitude at noon (the angle of the Sun above the horizon at noon)?

66.5 degrees

10. After the June solstice, will the subsolar point will move northward or southward?

Southward, toward the equator (reaching it in September), then to the Tropic of Capricorn (reaching it in December)

 

At the December Solstice - The date is December 21 or 22

1. The subsolar point is at what latitude?

23.5 degrees south

2. What is this latitude called?

The Tropic of Capricorn

3. What is the length of daylight at the equator?

12 hours; day length is always about 12 hours at the equator

4. What is the length of daylight at the North Pole?

0 hours; the North Pole has 24 hours of night on the December solstice, when the Sun does not rise above the horizon

5. What is the length of daylight at the South Pole?

24 hours; the Sun does not rise or set at the South Pole on the December solstice, it just circles around, 23.5 degrees above the horizon

6. On this day, every location north of what Circle is in darkness for 24 hours?

The Arctic Circle

7. Every location south of what Circle gets 24 hours of daylight?

The Antarctic Circle

8. It is the longest day of the year for which Hemisphere?

The Southern Hemisphere

9. At the equator, what is the Sun’s altitude at noon (the angle of the Sun above the horizon at noon)?

66.5 degrees

10. After the December solstice, will the subsolar point will move northward or southward?

Northward

 

At the March Equinox - The date is March 20 or 21

1. The subsolar point is at what latitude?

0 degrees

2. What is this latitude called?

The equator

3. What is the length of daylight at the equator?

12 hours

4. How many hours of daylight does every place on Earth get?

12 hours

5. At the equator, what is the Sun’s altitude at noon (the angle of the Sun above the horizon at noon)?

90 degrees

6. After the March equinox, will the subsolar point will move northward or southward?

Northward

7. In which Hemisphere is this the spring (vernal) equinox?

The Northern Hemisphere

8. In which Hemisphere is this the fall (autumnal) equinox?

The Southern Hemisphere

9. Will the days now be getting longer or shorter for the Northern Hemisphere?

Longer

10. Will the days now be getting longer or shorter for the Southern Hemisphere?

Shorter

 

At the September Equinox - The date is September 22 or 23

1. The subsolar point is at what latitude?

0 degrees

2. What is this latitude called?

The equator

3. What is the length of daylight at the equator?

12 hours

4. How many hours of daylight does every place on Earth get?

12 hours

5. At the equator, what is the Sun’s altitude at noon (the angle of the Sun above the horizon at noon)?

90 degrees

6. After the September equinox, will the subsolar point will move northward or southward?

Southward

7. In which Hemisphere is this the spring (vernal) equinox?

The Southern Hemisphere

8. In which Hemisphere is this the fall (autumnal) equinox?

The Northern Hemisphere

9. Will the days now be getting longer or shorter for the Northern Hemisphere?

Shorter

10. Will the days now be getting longer or shorter for the Southern Hemisphere?

Longer