The Sky Keeps Time
The Earth is closest to the Sun in January, yet that is the middle of winter in London. Work out why, then find out what raises two high tides a day, why the Moon is drifting away, how the small Moon can hide the whole Sun, what keeps the space station up and why spacecraft can leave for Mars only every two years or so. Fourteen investigations for ages 12 and up, in a live model of the real sky.
Library
A year round the Sun
Lesson 1
Closest to the Sun in January
The Earth is closer to the Sun in January than at any other time of year, so why is it winter in London?
StartLesson 2
The Sun That Wouldn't Set
In the north of Norway the Sun is still shining at midnight in late June: why doesn't it go down?
StartLesson 3
The Longer Half of the Year
March to September and September to March are each half the Earth's trip round the Sun, so why does the first take about a week longer?
StartThe Moon up close
Lesson 4
Where Is the Rest of the Moon?
Some evenings the Moon is only a thin, bright crescent, and the rest of it seems to have vanished.
StartLesson 5
Two High Tides, One Moon
The Moon pulls on the sea from one side of the Earth, so why do most beaches get two high tides a day?
StartLesson 6
The Side of the Moon We Never See
From the Earth we always see the same dark patches on the Moon, so is it spinning at all?
StartLesson 7
The Moon Is Drifting Away
Every year the Moon moves about four centimetres farther from the Earth: what could be pushing it?
StartEclipses
Lesson 8
The Missing Eclipses
The Moon passes between the Earth and the Sun once a month, so why don't we get an eclipse of the Sun every time?
StartLesson 9
How Can the Moon Hide the Sun?
The Sun is about 400 times wider than the Moon, yet in a total eclipse the Moon covers it almost exactly.
StartLesson 10
When the Moon Turns Red
Deep inside the Earth's shadow, where no sunlight should reach, the Moon still glows red: what is lighting it?
StartLeaving the Earth
Lesson 11
What Holds the Space Station Up?
Gravity at the space station's height is almost as strong as on the ground, yet the station stays up and the astronauts inside float.
StartLesson 12
Racing Round the Earth
The space station laps the Earth in an hour and a half, while the Moon takes a whole month: what sets the pace?
StartLesson 13
The 26-Month Wait for Mars
Missions to Mars leave in bunches, then none go for over two years: what are they waiting for?
StartLesson 14
Moving to Mars
On the Earth everything you need to stay alive comes free: what would you have to bring with you to Mars?
StartReview and assessment
Lesson 15
Test: The Sky Keeps Time
Review the course ideas by applying them to new situations, with kind feedback after every answer.
Locked till you take the prior lesson