Notes
Formation, Sun and planets
- The solar system formed 4.6 billion years ago from the solar nebula. 1 AU is about 150 million km.
- The Sun produces energy by hydrogen fusion. Layers: core, radiative zone, convective zone, photosphere, corona. Sunspots are cooler regions.
- Terrestrial planets are rocky; gas giants are Jupiter and Saturn; ice giants are Uranus and Neptune. Venus is hottest.
Small bodies
- Asteroids are mostly in the belt between Mars and Jupiter. Comets are icy and have tails pointing away from the Sun. Meteoroid, meteor, meteorite.
Earth-Moon-Sun
- Seasons result from Earth's 23.5° axial tilt, not distance.
- Phases come from the changing view of the Moon's lit half. Solar eclipses occur at new moon; lunar eclipses at full moon.
Topics in this unit
Each topic has its own short notes and practice.
Practice
Fusion converts mass to energy.
A thick CO₂ atmosphere traps heat.
$1.5 \times 150 = 225$.
Tilt changes sunlight angle and day length.
The side facing Earth is fully lit.
The Moon completely covers the Sun.
Free response
Write your answer first, then open the scoring guide.
Free-response question
In the Northern Hemisphere, it is June 21. A student studies the Sun, Earth and Moon. Light from the Sun takes 500 seconds to reach Earth at a speed of $3.0 \times 10^8$ m/s.
(a) Calculate the Earth-Sun distance in meters and state it in AU.
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$d = vt = 3.0 \times 10^8 \times 500 = 1.5 \times 10^{11}$ m, which is 1 AU.
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(b) Explain why June 21 is summer in the Northern Hemisphere and winter in the Southern Hemisphere.
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Earth's axis is tilted 23.5°; in June the Northern Hemisphere tilts toward the Sun so it gets more direct light and longer days, while the Southern Hemisphere tilts away.
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(c) Name the Moon phase at which a solar eclipse can occur and explain why it does not happen every month.
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New moon. The Moon's orbit is tilted about 5° to Earth's orbit, so the Moon's shadow usually passes above or below Earth.
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