← Space Without Formulas: From the Moon to Black Holes
Lesson
The Moon, the seasons, and weight on other worlds
Figure out why the seasons change, what weight and mass are, and why on the Moon you jump higher even though your mass stays the same.
Where the seasons come from
Not because of the distance to the Sun!
Many people think it's hot in summer because Earth is closer to the Sun, and cold in winter because it's farther away. That's wrong.
In fact, Earth's axis is tilted by about 23 degrees and always points the same way. Because of this, for half the year the Northern Hemisphere is turned toward the Sun, and for the other half, the Southern.
When your hemisphere is tilted toward the Sun, the rays hit more directly (almost straight down) and heat more strongly, and the day is longer — that's summer. When it's tilted away, the rays hit at a low angle, spread over a larger area and heat more weakly, and the day is shorter — that's winter.
The best proof: when it is summer in the United States, it is winter in Australia, and vice versa. If distance were the reason, the seasons would be the same everywhere. (A curious fact: Earth is actually a little closer to the Sun in January — that is, during winter in the Northern Hemisphere.)
Lesson notes
Not because of the distance to the Sun!
Many people think it's hot in summer because Earth is closer to the Sun, and cold in winter because it's farther away. That's wrong.
In fact, Earth's axis is tilted by about 23 degrees and always points the same way. Because of this, for half the year the Northern Hemisphere is turned toward the Sun, and for the other half, the Southern.
When your hemisphere is tilted toward the Sun, the rays hit more directly (almost straight down) and heat more strongly, and the day is longer — that's summer. When it's tilted away, the rays hit at a low angle, spread over a larger area and heat more weakly, and the day is shorter — that's winter.
The best proof: when it is summer in the United States, it is winter in Australia, and vice versa. If distance were the reason, the seasons would be the same everywhere. (A curious fact: Earth is actually a little closer to the Sun in January — that is, during winter in the Northern Hemisphere.)
Mass is how much matter there is in an object. It doesn't change wherever you are: on Earth, on the Moon, or in weightlessness.
Weight is how hard you press on whatever supports you because of gravity. Your weight depends on which planet you're standing on.
The Moon's gravity is about 6 times weaker than Earth's. So on the Moon you would weigh 6 times less: a person who “weighs” 60 kg would feel like 10 kg and could jump much higher. But they would contain exactly as much matter as before — their mass wouldn't change.
A tricky question: which is heavier on the Moon — a kilogram of feathers or a kilogram of iron? The answer is the same as on Earth: they weigh the same. A kilogram is a kilogram. The only thing that changes is that on the Moon both of them press on the scale more weakly than on Earth.