Year 7 Science | Victorian Curriculum 2.0
Earth, Sun & Moon: seasons, eclipses, tides
Topic 05 | Earth and space sciences | Answer key

Year 7 answers

Fluency

Tier 1: recall and identify

    1. 2424 hours to rotate; about 365.25365.25 days to orbit the Sun.
    2. Earth rotates on its axis; at any moment half faces the Sun (day) and half faces away (night).
    3. Earth’s axis is tilted 23.5°23.5°, so each hemisphere gets more direct sunlight and longer days during its summer.
    4. 23.5°23.5°.
    5. New Moon, waxing crescent, first quarter, waxing gibbous, full Moon, waning gibbous, last quarter, waning crescent.
    6. About 29.529.5 days.
    7. Sun, Moon, Earth in a line (Moon between Sun and Earth). Happens at New Moon.
    8. Sun, Earth, Moon in a line (Earth between Sun and Moon). Happens at Full Moon.
    9. Two high tides (and two low tides) per day.
    10. A tide with a larger than usual range, occurring at New or Full Moon when Sun and Moon are aligned.
Reasoning

Tier 2: explain and reason

    1. The hemisphere tilted towards the Sun sees the Sun rise earlier and set later because more of its latitudes are on the sunlit side of the Earth during rotation.
    2. The ground and oceans take weeks to heat up, so peak temperature lags the peak of sunlight. This is called seasonal lag.
    3. The Moon’s orbit is tilted about 5°5° from Earth’s orbit around the Sun, so at most New Moons the Moon passes above or below the Earth-Sun line, missing the alignment needed for an eclipse.
    4. (a) Full Moon: Sun - Earth - Moon in a line (Earth between). (b) First quarter: Sun, Earth and Moon form a right angle at Earth.
    5. Earth’s atmosphere bends (refracts) red sunlight around into the shadow. Blue light is scattered away, leaving the Moon lit by deep red light — hence “blood Moon”.
    6. Tidal bulges require large bodies of water stretched across distances where the Moon’s pull differs enough to matter. Lakes are too small for significant differential pull, so their tidal change is millimetres.
Reasoning

Tier 3: apply to a novel context

    1. With zero tilt: (i) no seasons — each latitude’s weather would be roughly the same all year. (ii) Equal day and night everywhere year-round. Agriculture, migration, and biodiversity would all change.
    2. Yes — the Sun’s gravity produces solar tides too, roughly half the size of Moon tides. Without a moon, tides would still exist but would be smaller and only driven by the Sun.
    3. New Moon or Full Moon — spring tides occur then, giving the biggest range between high and low.
    4. Martian seasons last about 2×2\times as long as Earth’s because a Mars “year” is nearly twice as long. The temperature pattern is similar (tilted-towards hemisphere has summer) but the orbit is more elliptical, so seasons have unequal length in different hemispheres.
Reasoning

Challenge

    1. (a) As the Moon recedes, tidal friction slows Earth’s rotation — days get longer. (b) Weaker pull at greater distance means the tidal bulges shrink, so tides become smaller.
    2. A calendar month is 2828-3131 days, slightly longer than the 29.529.5-day lunar cycle. Occasionally two Full Moons fit in the same month — the second is called a blue Moon. Happens roughly every 2.72.7 years.
    3. Every New Moon — about once every 29.529.5 days. Because the orbit is tilted, the Moon usually misses the alignment; if the tilt were zero the alignment would happen every lunar cycle.
    4. Stand in a dark room. Hold a small ball (Moon) at arm’s length and slowly orbit around a student (Earth) while a torch (Sun) shines from one side. Observer sees different lit portions as the Moon orbits. Limitation: the scale is wrong — in reality the Moon is far smaller and much further away than this model suggests, and the model cannot demonstrate why eclipses are rare.
Year 7 Science study companion | Answer key