Year 7 Science · Unit 4 · Lesson 8
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Learning Goals
1. By about how many degrees is the Earth’s axis tilted? Does the direction it points change as the Earth orbits the Sun?
Compare rotation and orbit
Complete the table. One mark for each row with both cells correct.
| Question | Rotation | Orbit |
|---|---|---|
| What does the Earth do? | ||
| What does it cause? | ||
| How long does one take? | ||
| About how many happen in one year? |
2. One orbit takes about 365.25 days, but a normal calendar year has 365 days. How many extra days do the quarter days add up to over 12 years? How many leap years does the calendar need in that time?
Extra days days
Leap years
Cause and effect: summer in Australia
Fill the two empty boxes. Each box is caused by the one before it, and row 2 carries on from the end of row 1.
Read the data: daylight in Sydney
Scenario: a year of daylight
A student looked up how many hours of daylight Sydney gets on the 21st day of every second month.
| Date | 21 Dec | 21 Feb | 21 Apr | 21 Jun | 21 Aug | 21 Oct |
|---|---|---|---|---|---|---|
| Daylight (hours) | 14.4 | 13.2 | 11.1 | 9.9 | 11.1 | 13.2 |
Source: rounded values calculated for Sydney.
3. Plot the data from Table 1 as a line graph, with the dates in order along the horizontal axis. Label both axes.
4. Describe the pattern in your graph. Use the tilt of the Earth’s axis to explain why Sydney has the fewest hours of daylight in June.
5. A school prints next year’s calendar, showing sunrise times and the first day of each season. A parent asks: “How can anyone know these a whole year ahead?” Write a reply that uses rotation, orbit and tilt.
Question 1
About 23.5 degrees (1). No: the axis keeps pointing the same way all year (1). [2 marks]
Compare rotation and orbit
Spins on its axis / travels around the Sun (1). Day and night / the year (1). About 24 hours / about 365.25 days (1). About 365 / one (1). [4 marks]
Question 2
12 × 0.25 = 3 days (1); so 3 leap years, one every four years (1). [2 marks]
Cause and effect: summer in Australia
Box 1: sunlight hits Australia more directly and the days are longer (1). Box 2: the Sun’s energy is concentrated on the ground, so it heats up more (1). [2 marks]
Read the data: daylight in Sydney
3. Axes labelled (date; daylight in hours) with an even scale (1); six points plotted correctly (1); points joined and a title (1). [3 marks]
4. Daylight falls from 14.4 h in December to 9.9 h in June, then rises again (1). In June the Southern Hemisphere is tilted away from the Sun (1), so Sydney gets slanted sunlight and shorter days (1). [3 marks]
Question 5
Marking guide: 1 the Earth rotates at a steady rate, once about every 24 hours; 1 so sunrise times can be worked out ahead; 1 the orbit takes about 365.25 days and repeats; 1 the tilt stays the same, so the seasons come at the same time each year; 1 steady, repeating cycles can be predicted far ahead; 1 uses predictable correctly and answers the parent. [6 marks]
Model answer: The Earth rotates at a steady rate, once about every 24 hours, so sunrise times can be worked out in advance. It orbits the Sun every 365.25 days with its axis tilted the same way, so the seasons arrive at the same time each year. These motions repeat in regular cycles, so the calendar is predictable.
Common error: swapping rotation and orbit, or their times.