Space and gravity, Year 7: more practice

6

提示Divide the angle by the angle turned each hour.

为什么90 ÷ 15 = 6 hours. A full turn of 360° takes 24 hours.

The spinning of the Earth

提示Which body is really moving?

为什么The Earth rotates once a day, so the Sun seems to cross the sky from east to west.

Your part of the Earth is facing away from the Sun

提示Half of the planet is always lit.

为什么As the Earth turns, your place moves into the half that faces away from the Sun, which is in shadow.

Winter

提示The two hemispheres lean in opposite ways.

为什么When the northern hemisphere is tilted towards the Sun, the southern hemisphere is tilted away from it.

The light is spread over a smaller area

提示Think of a torch shone straight down or at a slant.

为什么A higher Sun means the rays hit the ground more steeply and are concentrated on a smaller area, so each square metre receives more energy.

Summer

提示Think about which hemisphere is tilted towards the Sun.

为什么The northern hemisphere leans towards the Sun in summer, so the Sun spends longer above the horizon. Longest day is about 21 June.

Mercury

提示It is also the smallest planet.

为什么Mercury orbits closest to the Sun.

Jupiter

提示It is a gas giant.

为什么Jupiter is more massive than all the other planets combined.

Venus

提示A thick atmosphere traps heat.

为什么Venus's atmosphere of carbon dioxide traps heat, making it hotter than Mercury, even though Mercury is nearer the Sun.

Neptune

提示The Solar System's last planet.

为什么Neptune is the eighth and outermost planet.