Seasons & Earth's Tilt — Drills · Grade 9 Science

Chapter: Earth, Moon & Solar System

What these drills covers

By the end of Seasons & Earth's Tilt you should be able to:

8 questions, multiple choice, numeric and written answer, each with a worked explanation.

Vocabulary used: axis, tilt, solstice, equinox.

Problem 1

Seasons are caused mainly by
  1. Earth's distance from the Sun
  2. the tilt of Earth's axis
  3. the Moon
  4. solar flares
Answer and explanation

the tilt of Earth's axis

The roughly 23.5° tilt changes how directly sunlight strikes each hemisphere through the year.

Problem 2

By how many degrees is Earth's axis tilted, to one decimal place?
Answer and explanation

23.5 degrees

About 23.5° from the perpendicular to its orbital plane.

Problem 3

When the northern hemisphere has summer, the southern hemisphere has
  1. summer
  2. winter
  3. spring
  4. no season
Answer and explanation

winter

The hemispheres are tilted oppositely relative to the Sun at any moment.

Problem 4

Summer is warmer mainly because sunlight
  1. travels a shorter distance
  2. strikes more directly and for more hours
  3. is a different colour
  4. passes through less atmosphere only
Answer and explanation

strikes more directly and for more hours

Directness concentrates energy over a smaller area, and longer days increase the total received.

Problem 5

At an equinox
  1. day and night are roughly equal everywhere
  2. the Sun never sets
  3. the tilt is zero
  4. Earth is closest to the Sun
Answer and explanation

day and night are roughly equal everywhere

Neither hemisphere is tilted toward the Sun, so day and night are nearly equal.

Problem 6

Earth is actually closest to the Sun in early January. This shows that
  1. distance causes seasons
  2. distance is not the main cause of seasons
  3. the tilt does not matter
  4. January is hottest everywhere
Answer and explanation

distance is not the main cause of seasons

The northern hemisphere has winter then, so distance cannot be the explanation.

Problem 7

Explain why the equator has little seasonal temperature variation.
Answer and explanation

Near the equator the Sun is high in the sky all year and day length barely changes, so the amount of solar energy received per unit area stays nearly constant through the year. The tilt that produces strong seasons at higher latitudes has little effect there, which is why equatorial regions vary more between wet and dry seasons than between hot and cold.

Response criteria

  • State a scientifically accurate conclusion.
  • Show the data, mechanism, or calculation that supports it.
  • Include units, conditions, or limits where relevant.

Problem 8

Explain how both day length and the angle of sunlight contribute to summer warmth.
Answer and explanation

When a hemisphere is tilted toward the Sun, sunlight arrives at a steeper angle, so a given beam is concentrated on a smaller area of ground and delivers more energy per square metre. The same tilt also puts that hemisphere in sunlight for more hours each day. The two effects reinforce each other: more intense sunlight for longer, which is why the seasonal difference is large.

Response criteria

  • State a scientifically accurate conclusion.
  • Show the data, mechanism, or calculation that supports it.
  • Include units, conditions, or limits where relevant.

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