Antarctica: Twilight zone
In this sequence of learning, find out about the significant variation in sunlight hours that occur across Antarctica and in comparison to other locations on Earth. Interpret graphs of daylight hours. Compare hours of daylight and darkness received by places at different locations across Antarctica, Australia and the world. Investigate the relationship between a locality, the hours of daylight it receives and its temperature range. Investigate the reasons for variability of sea ice coverage around Antarctica. Find out what causes the changes in seasons across Earth.
Setting the scene
Winter and summer days
Show this timelapse video of an Antarctic summer day. Predict what you would observe in an Antarctic winter sky compared with what you saw in an Antarctic summer sky. Discuss and ask the students to give reasons for their observations.
Then show this timelapse of an Antarctic winter day.
Daylight hours across the year
Establish that daylight hours are measured from sunrise to sunset. Pose the questions, ‘How do the hours of daylight vary across the year where we live?’ Are there more hours of daylight at a particular time of the year? Use think-pair-share strategy:
Individually (Think) students think about at what time the sun rises and sets in summer and in winter. They predict the hours of daylight for December and June. In pairs, (Pair) students sketch a line graph of what they expect daylight hours to look like over a year. Suggest that they plot a point for the middle of each month to show their predicted average daylight hours for that month. Combine pairs (Share) to share ideas, review and create a final graph.
How does your location influence hours of daylight during a year? Provide the worksheet, Daylight hours for Hobart and Cairns [PDF]. Calculate the daylight hours from the sunrise and sunset times. What trends are similar? What differences do they note between locations? What might be a reason for the differences?
Explore and research
Sunlight hours: Antarctic region
Review latitude and show how this indicates the north-south location of a place on a globe of the Earth. Explain that places with latitude (° S) indicate that it is below the equator. Show examples: Cairns Lat. 16.9° S, Brisbane Lat. 27.4° S, Sydney Lat. 33.8° S, Melbourne Lat. 37.8° S and Hobart Lat. 42.8° S. Note the pattern; the further from the equator the higher the latitude. The Antarctic Circle is 66.5° S. The South Pole latitude is 90° S.
Highlight the latitude of your own location.
Provide the article: Sunlight hours: How much daylight is there in Antarctica during summer and winter?
Interpret the graphical representations for each location in the Antarctic region described in the article. What does the shading indicate? Discuss the different stages of twilight, hours of daylight and darkness. For example at the South pole (90° S):
- 24 hours of darkness each ‘day’ between much of May and July
- only experiences twilight from mid-March to mid-May and in August and September.
- 24 hours of daylight each ‘day’ from September to mid-March.
Use this interactive resource: Seasons: latitude to explore daylight hours of locations based on their latitude.
Investigate the shortest day (winter solstice), the longest day (summer solstice) and the two days of the year with equal hours of day and night (equinox). When does this occur in Antarctica?
Locate Mawson station, Antarctica, on a map and highlight its latitude.
Provide climate data for Mawson [PDF]. Refer to the worksheet, Mean temperature and hours of sunshine for Mawson, Antarctica [PDF]. Discuss the trend in temperature across the year. How does this trend compare with the hours of daylight experienced at Mawson? Investigate and describe the relationship between temperature and hours of daylight.
Explain and share
Modelling Earth and Sun
Demonstrate Earth’s rotation on its tilted axis, using a globe of the Earth and a strong light source in a darkened room. Show how the sun rises in eastern states before those in the west. Look at the position of Australia in summer and the angle of sunlight it receives compared to six months later in its orbit of the Sun (winter). Ask students to represent how the Earth’s position in its orbit of the Sun influences seasons on Earth.
Angle of sunlight
Investigate the effect of the angle of sunlight hitting the Earth. Use a torch and a sheet of grid paper marked in 1 cm squares. Mark and measure the area illuminated by the torch when shone perpendicular (90 degrees) to the grid. From the same distance, angle the torch at about 45 degrees. Mark and measure the area illuminated by the torch. Explain the effect of spreading the energy over a greater surface area. Use this investigation to explain what happens to the Sun’s energy as it strikes Antarctica compared with other locations on Earth. Note that the sunlight also strikes the atmosphere at more of an angle that at the equator for example. Consider the effect this may also have on heating of the Earth at different locations.
Assess the students’ understanding of the effect of the angle of the sun’s light striking the earth: Sun’s energy assessment.
Elaborate and apply
Seasons and sea ice
Throughout the seasons, the coverage of sea ice surrounding Antarctica changes.
Investigate the variability of sea ice around Antarctica. Show these maps of Antarctica which show the average minimum and maximum sea ice coverage. Discuss the increase in size of Antarctica due to sea ice coverage in winter compared with that in summer.
Relate the changes in sea ice coverage to air and water temperatures, wave action and ocean currents.
Guide students’ research by reviewing information on sea ice.
Assess students’ understanding of how daylight varies as a result of Earth’s tilt and its orbit around the Sun. This resource provides an electronic copy of the students’ answers.
A call to Cairns
You are based in Mawson for the year. Your friend lives in Cairns and you are in regular communication. You often talk about the weather and the conditions you have to face. In comparison your friend boasts about the conditions they are living in. Describe your conversation for these dates of your call: 22 June, 22 September and 22 December.
Rich task: Visiting Antarctica
Introduce the task: You are a tourist organiser in charge of planning a trip to view wildlife near one of the scientific research stations. Describe the climate challenges for this type of travel, when the most suitable time might be during the year and other considerations you would include. Provide a list of conditions you would expect to encounter.
Design a brochure to advertise the trip. Outline safety measures, terrain and climate challenges. Include maps and images.
At various points in the learning assess to what extent students:
- describe seasonal differences such as daylight hours, temperature and influence on climate at different locations
- explain the causes for seasons