Earth and space (grade 8) · lesson

Moon phases

💡 Half the moon is always lit by the sun, and its phases show how much of that lit half faces us.

The moon makes no light of its own. It reflects sunlight. The half facing the sun is always lit.

As the moon orbits Earth, we see different amounts of its lit half. That makes the phases.

After a new moon, the lit part grows, or waxes: crescent, first quarter, gibbous, then full. At full moon, the whole lit side faces Earth.

🧠 Let's work it out

Use a ball and a lamp as a model.
Walk the ball around your head.
When the ball is between you and the lamp, you see its dark side: new moon.
When you are between, you see its lit side: full moon.

What do you think comes next?

phase: the shape of the lit part of the moon that we see
waxing: growing larger

Eclipses

💡 An eclipse happens when the sun, Earth, and moon line up so one casts a shadow on another.

In a solar eclipse, the moon passes between the sun and Earth. Its shadow falls on Earth. This can only happen at new moon.

In a lunar eclipse, Earth is between the sun and the moon. Earth's shadow falls on the moon. This can only happen at full moon.

The moon's orbit is tilted a little. So most months it passes above or below the shadow. That is why we don't get an eclipse every month.

🧠 Let's work it out

Ask what is blocking what.
To block the sun from us, something must be between us and the sun.
That is the moon, so a solar eclipse puts the moon in the middle.

What do you think comes next?

solar eclipse: the moon blocks the sun from part of Earth
lunar eclipse: Earth's shadow falls on the moon

🔗 NASA Space Place: Lunar and solar eclipses · NASA ↗

Seasons

💡 Seasons are caused by the tilt of Earth's axis, not by Earth's distance from the sun.

Earth's axis is tilted. As Earth orbits the sun, first one half and then the other tilts toward the sun.

The half tilted toward the sun gets more direct sunlight and longer days. It has summer. The other half has winter at the same time.

Earth's distance from the sun changes only a little. In fact, Earth is a little farther from the sun in early July.

🧠 Let's work it out

Test the distance idea against facts.
If distance caused seasons, both halves would have summer at once.
But the north and south have opposite seasons.

What do you think comes next?

axis: the imaginary line Earth spins around

🔗 NASA Space Place: What causes the seasons? · NASA ↗

Gravity and orbits

💡 The sun's gravity keeps the planets in orbit, and planets farther out take longer to go around.

Gravity pulls the planets toward the sun. That pull keeps them moving in orbit instead of flying off into space.

Planets farther from the sun travel a longer path. They also feel a weaker pull and move more slowly. So they take longer to orbit.

🧠 Let's work it out

Line up the data.
Mercury is 0.4 AU and takes 0.24 years.
Earth is 1 AU and takes 1 year.
Jupiter is 5.2 AU and takes 11.9 years.

What do you think comes next?

orbit: the path of one object around another
AU: the distance from Earth to the sun, used to measure space

🔗 PhET simulation: Gravity and Orbits · PhET Interactive Simulations ↗

Scale models

💡 A scale model shrinks every size by the same factor, so sizes keep the same ratios.

Space objects are too big to picture. A scale model makes them small enough to compare.

To keep the model true, multiply or divide every size by the same number.

🧠 Let's work it out

Use the ratio.
Jupiter is about 11 times as wide as Earth.
If Earth is a 1 cm marble, Jupiter is 11 × 1 cm = 11 cm.

What do you think comes next?

scale model: a model where every size is changed by the same amount

Reducing human impact

💡 The best plans to cut pollution stop it at its source or catch it before it spreads.

People's actions can pollute air and water. Car exhaust dirties the air. Lawn fertilizer washes into streams and makes algae grow out of control.

Good plans cut pollution at its source. Using less fertilizer, or taking buses and bikes instead of cars, means less pollution is made.

Other plans catch pollution before it spreads. A strip of plants along a stream soaks up runoff before it reaches the water.

🧠 Let's work it out

Test each plan with one question: does it mean less pollution reaches the air or water?
More bike lanes: fewer cars, so yes.
More parking lots near a stream: more fast runoff, so no.

What do you think comes next?

runoff: rainwater that flows over land into streams