IGCSE 0625 · SPACE · 6.1

The Earth and the Solar System

Day, year, and seasons, the Sun and its eight planets, how gravity holds objects in orbit, and comets. It builds on mass, weight, and forces from Topic 1 and leads into stars and the Universe.

TOPIC 6.1: THE EARTH AND THE SOLAR SYSTEM CAMBRIDGE IGCSE PHYSICS 0625 · PATHWAYS TheLucidSTEM · thelucidstem.com BUILDS ON 1.3 Mass & weight 1.5 Forces LEADS TO 6.2 Stars & Universe Gravity & orbits SOLAR SYSTEM 1 · DAY, YEAR & SEASONS The Earth spins and orbits, and the Moon orbits the Earth. One spin on its axis takes a day. One orbit of the Sun takes a year. The Moon orbits in about a month; we see phases as sunlight lights up different parts of it. The tilt of the axis gives us the seasons. Sun Earth Moon 2 · THE SOLAR SYSTEM The Sun and eight planets, held together by the Sun's gravity. Four small rocky planets lie closest in. Four large gas and ice giants lie further out. There are also moons, asteroids, and comets. Orbits are slightly elliptical, not exact circles. rocky planets near, giants further out 3 · GRAVITY & ORBITS Gravity provides the force that holds objects in their orbits. The pull is toward the centre of the orbit. It is weaker at greater distances. Planets further out move slower and take longer. Orbital speed (Extended): v = 2πr / T r = orbit radius T = period v gravity 4 · COMETS & SCALE The Solar System is mostly empty space. The Sun holds almost all of the mass. A comet has a long, stretched, elliptical orbit: it speeds up near the Sun and slows far away. Distances are so vast that sunlight takes minutes to hours to cross the Solar System. Sun comet tail
TOPIC 6.1: THE EARTH AND THE SOLAR SYSTEM CAMBRIDGE IGCSE PHYSICS 0625 · PATHWAYS TheLucidSTEM · thelucidstem.com BUILDS ON 1.3 Mass & weight 1.5 Forces LEADS TO 6.2 Stars & Universe Gravity & orbits SOLAR SYSTEM 1 · DAY, YEAR & SEASONS The Earth spins and orbits, and the Moon orbits the Earth. One spin on its axis takes a day. One orbit of the Sun takes a year. The Moon orbits in about a month; we see phases as sunlight lights up different parts of it. The tilt of the axis gives us the seasons. Sun Earth Moon 2 · THE SOLAR SYSTEM The Sun and eight planets, held together by the Sun's gravity. Four small rocky planets lie closest in. Four large gas and ice giants lie further out. There are also moons, asteroids, and comets. Orbits are slightly elliptical, not exact circles. rocky planets near, giants further out 3 · GRAVITY & ORBITS Gravity provides the force that holds objects in their orbits. The pull is toward the centre of the orbit. It is weaker at greater distances. Planets further out move slower and take longer. Orbital speed (Extended): v = 2πr / T r = orbit radius T = period v gravity 4 · COMETS & SCALE The Solar System is mostly empty space. The Sun holds almost all of the mass. A comet has a long, stretched, elliptical orbit: it speeds up near the Sun and slows far away. Distances are so vast that sunlight takes minutes to hours to cross the Solar System. Sun comet tail
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