Exercises: Earth's Tilt, Revolution and the Seasons

Earth takes about 365 days to travel once around the Sun. Name this motion of Earth around the Sun. Then name the motion that causes day and night, and say how long it takes.

Earth's axis is tilted about $23.5^\circ$ from straight up and down compared with its path around the Sun. In one or two sentences, explain what this tilt means and say whether the tilt direction stays the same during the whole year.

Emma lives in Denver, Colorado, in the Northern Hemisphere. On June 21 her family notices that the day is very long and the Sun is high in the sky. Which season is starting in Denver? Which season is starting at the same time in Australia, in the Southern Hemisphere?

A classmate says, "It is hot in summer because Earth is closer to the Sun." Explain why this idea is incorrect. In your answer, use the tilt of Earth's axis and the directness of sunlight. Include what happens to the length of daylight in the Northern Hemisphere in summer.

Jayden shines a flashlight straight down onto a sheet of paper, and then shines it at a slant from the same distance. The straight beam makes a small, bright circle. The slanted beam makes a larger, dimmer oval. Explain how this model shows why the Sun's rays heat Earth more in summer than in winter. Say what the flashlight, the paper and the slant represent.

The table shows approximate hours of daylight in Houston, Texas, on four dates.

1. a) Which date is closest to the start of summer and which to the start of winter? b) By how many hours does the longest day differ from the shortest day? c) Explain what position of Earth's tilt relative to the Sun causes the longest day.

Draw or describe a model showing Earth at four points in its orbit around the Sun: positions A, B, C and D, each about three months apart. At position A the Northern Hemisphere is tilted toward the Sun. For each position, state which hemisphere receives more direct sunlight and name the season in the Northern Hemisphere. Then explain why the seasons would NOT happen in the same way if Earth's axis had no tilt at all, even though Earth still revolved around the Sun.

Earth is closest to the Sun in early January, at about 147 million km, and farthest in early July, at about 152 million km. Mateo claims this proves distance causes the seasons. Use these facts and what you know about seasons in both hemispheres to write an argument (claim, evidence, reasoning) that evaluates Mateo's claim. Explain what would be different about July weather in Chicago and in Buenos Aires, Argentina, if distance were the cause.