Science and Technology K–6 · Year 6

Globe and lamp: why winter days are shorter

Science understanding: Earth and space sciences

Practical, model not builtLow risk

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The idea

Earth spins on an axis tilted 23.4 degrees from the perpendicular to its orbit, so the axis itself stands 66.6 degrees from the plane of the orbit, and it keeps pointing the same way in space, so as Earth goes round the Sun each hemisphere spends more or less of each turn in sunlight, giving long summer days and short winter days.

What you need

a globe on a stand tilted at 23.4 degrees, about 20 cm across (or a 20 cm foam ball on a skewer tilted with a protractor)
a lamp with a bare LED globe at the globe's height, or a strong torch on a stand
masking tape to mark four positions on a 2 m radius circle on the floor around the lamp
small stickers for Sydney (33.9 degrees south), Darwin (12.5 degrees south) and Hobart (42.9 degrees south)
a strip of paper tape laid around the globe along Sydney's line of latitude, and a ruler
the Geoscience Australia sunrise and sunset calculator for your town
a darkened room

How to do it

Mark four positions around the lamp, a quarter of a circle apart: June solstice, September equinox, December solstice and March equinox. Stand the globe at the June mark with its axis tilted and the South Pole leaning away from the lamp.
Carry the globe to each mark in turn, keeping the axis pointing at the same wall of the room every time.
At each mark, hold the globe still and mark on the paper tape the two points where the edge of the lit side crosses Sydney's latitude. Measure the lit length and the whole length of the tape.
Work out the model day length: lit length / whole length x 24 hours. Record it for all four positions.
Repeat for Darwin and Hobart at the June and December marks.
Look up the real sunrise and sunset times for 21 June and 21 December and compare them with your model.
Explain why Hobart's day length changes most through the year and Darwin's least.

What you should see

At the June mark the southern hemisphere tilts away and less than half of Sydney's circle is lit; at December more than half; at the equinoxes half. The real Sydney day, sunrise to sunset of the Sun's top edge with atmospheric refraction, is 9 h 54 min at the June solstice, 14 h 25 min at the December solstice and 12 h 08 min at an equinox (the geometric values are 9 h 45 min, 14 h 15 min and 12 h 00 min). A lamp 2 m from a 20 cm globe lights slightly less than half of it, so the model's days come out about half an hour short (9.2, 11.5 and 13.7 hours), and the differences between seasons are what the model gets right. Hobart swings from 9 h 01 min to 15 h 21 min and Darwin only from 11 h 23 min to 12 h 51 min.

What changes

What you change: position of Earth in its orbit (date) and latitude
What you measure: fraction of the latitude circle lit, as hours of daylight
What you keep the same: axis tilt 23.4 degrees
axis direction fixed in the room
lamp distance 2 m
same globe

Common misconceptions

Each of these ideas is wrong, and the activity is a chance to test it.

Winter days are short because Earth is farther from the Sun (Earth is closest to the Sun in early January, in the southern summer).
Earth's axis tilts toward the Sun in summer and swings the other way in winter (it points the same way in space all year).
Every place has 12 hours of day and 12 of night.

Safety card

Low riskLearners carry it out

Hazards

dark room trip hazard
hot lamp housing

Controls

clear the floor and tape leads down
LED lamp, not a halogen
no one looks into the lamp

Note

Risk assessment before the lesson using Primary RiskAssess or the school's own template.

Curriculum references

The NSW syllabus outcomes and Australian Curriculum v9 codes this activity supports. They are references, not a verified or complete curriculum alignment.

Science and Technology K-6 Syllabus (2017), current, taught until 2026; a Stage 2 outcome, because the nearest NSW content is the Stage 2 content on the Earth and the Sun ('investigate how the Earth's rotation on its axis causes regular changes including night and day' and 'compare times for the Earth to orbit the Sun'), and neither the Stage 3 content under ST3-10ES-S, which is the planets of our solar system and sudden geological and extreme weather change, nor the 2024 Stage 3 content covers Earth's tilt, the seasons or the changing length of the day; code read from the syllabus document on 22 September 2026ST2-10ES-S
Science and Technology K-6 Syllabus (2017), current, taught until 2026; code read from the syllabus document on 22 September 2026ST3-1WS-S
Science and Technology K-6 Syllabus (2024), implemented from 2027; NESA's timeline is 2026 plan and prepare and 2027 start teaching, and schools may choose to implement it during 2026; code read from the outcomes page on 22 September 2026ST3-DAT-01
Australian Curriculum v9AC9S6U02AC9S6I01AC9S6I04AC9S6I05

Sources

The pages the author read to write this activity.

All Concept Studio activities