← Teacher guides

Teacher guide: Year 7 Earth and space

The Earth, sun and moon as one system of cycles: spinning and orbiting, seasons from a tilted axis, the moon's phases, eclipses, and tides. Concept tutorials with a live model seen from above and from the side.

Open the student course

Each lesson works two ways. Students can work through the online tutorial at their own pace (it checks their answers and saves their progress in their browser), or you can teach it to the whole class from the slides, then send students into the tutorial for the Modify and Make steps.

Every lesson guide has plain-language notes, the answers to every check, a solution for every task, and slides and a worksheet for Waypoints Prepare. These guide pages are not linked from student pages, but they are not secret either: keep printed Teacher editions for answers you do not want students to find.

The Earth and the sun

Rotation, revolution and the tilted axis; seasons (AC9S7U03).

The Earth and the sun in 5 minutes (read before teaching this unit)

The idea in plain words

  • Rotation: the Earth spins on its axis once a day (anticlockwise seen from above the North Pole), so the sun rises in the east and sets in the west. Day is the half facing the sun.
  • Revolution: the Earth goes round the sun once a year (about 365¼ days), spinning about 365 times on the way.
  • Tilt: the axis is tilted 23.4° and keeps pointing the same way in space all year (towards the Pole Star). So for half the year the Southern Hemisphere leans towards the sun, and for the other half it leans away.
  • Seasons come from the tilt, not from distance. Leaning towards the sun means the sun is higher at noon (its light is concentrated on a smaller area) and the days are longer: summer. The Earth is actually closest to the sun in early January, in Australia's summer and the Northern Hemisphere's winter.
  • The two hemispheres have opposite seasons at the same time. Near the equator, day length and the noon sun change little, so there is no strong summer and winter.

Where the picture breaks

  • Sizes and distances on the board are not to scale: the sun is about 109 times wider than the Earth and about 12 000 Earth-widths away.
  • The side view shows only the tilt towards or away from the sun; the rest of the tilt is towards or away from you.
  • Day lengths ignore the bending of light by the air, so real days are a few minutes longer.

Common misconceptions

  • Seasons happen because the Earth is closer to the sun in summer.
  • The sun goes round the Earth each day, or the Earth goes round the sun once a day.
  • The axis wobbles towards the sun in summer (it doesn't change direction; the Earth moves to the other side of the sun).
  • Summer days are hotter because the sun is "bigger" or "stronger".

Investigate in class

Optional ideas if you run a practical for this unit: pick one, adapt it to your equipment, or use your own.

  • Does the angle of the light change how much a surface warms? Change: the angle a lamp shines on black card (90°, 60°, 30°). Measure: the temperature under the card after 10 minutes. Keep the same: the lamp, its distance, the time. (A model of a high and a low noon sun.)
  • Does a shadow change length through the day? Change: the time of day. Measure: the shadow length of a 1 m stick in the playground. Keep the same: the stick, its spot. (The shortest shadow is near midday.)
  • Do places further from the equator have a bigger change in day length? Secondary data: published sunrise and sunset times. Change: the city (Darwin, Brisbane, Canberra, Hobart). Measure: day length on 21 June and 21 December. Keep the same: the dates.

Safety and ethics: never look at the sun, even through sunglasses; lamps get hot.

The moon

Phases, eclipses and tides (AC9S7U03).

The moon in 5 minutes (read before teaching this unit)

The idea in plain words

  • The sun always lights half of the moon. As the moon goes round the Earth (about 29.5 days from new moon to new moon), we see different amounts of that lit half: the phases. They are not caused by Earth's shadow.
  • Order: new moon, waxing crescent, first quarter, waxing gibbous, full moon, waning gibbous, last quarter, waning crescent. From Australia a waxing moon is lit on the left; from the Northern Hemisphere, on the right.
  • Solar eclipse: at new moon, the moon is between the sun and Earth and its shadow falls on part of Earth. Lunar eclipse: at full moon, the Earth is between the sun and moon and the moon passes through Earth's shadow. The umbra is the dark central shadow (total eclipse); the penumbra is the outer partial shadow.
  • Eclipses don't happen every month because the moon's orbit is tilted about 5°: most new and full moons pass above or below the line to the sun. Eclipses happen only in "eclipse seasons" about every six months, when the line where the orbits cross points at the sun.
  • Tides: the moon's gravity pulls the oceans into two bulges (one facing the moon, one on the far side); the Earth spins through both, giving most coasts two high tides a day. The sun adds a smaller effect: spring tides (biggest range) at new and full moon when the sun and moon line up; neap tides (smallest range) at the quarters.

Where the picture breaks

  • Distances and sizes are not to scale; in the eclipse side view the tilt and the shadows are exaggerated so that they can be seen.
  • The ocean bulges are hugely exaggerated, and real tides are shaped by coastlines and seafloor (some places have one tide a day).
  • The board's tide chart is for an idealised coast: real tide tables also vary with the moon's distance.

Common misconceptions

  • Phases are caused by Earth's shadow.
  • A lunar eclipse is just a new moon (or a moon phase).
  • Eclipses should happen every month.
  • There is one tidal bulge, under the moon, so one high tide a day.
  • "Spring tides" happen in spring.

Investigate in class

Optional ideas if you run a practical for this unit: pick one, adapt it to your equipment, or use your own.

  • Does where the moon is in its orbit change how much of its lit half we see? A model in a dark room: a lamp (sun), a ball on a pencil (moon), a student's head (Earth). Change: the ball's position around the head (eight places). Record: the lit shape seen. Keep the same: the ball's height.
  • Does the moon's shape change over two weeks? Change: the date. Record: the shape and which side is lit. Keep the same: the time of night and the place you look from. (A home task.)
  • Is the tidal range bigger at full and new moon? Secondary data: Bureau of Meteorology tide predictions for a nearby port. Change: the day of the month. Measure: high tide minus low tide. Keep the same: the port.

Safety and ethics: never look straight at the sun when spotting the moon by day; the lamp gets hot.