Newton, Kepler, Galileo
Ova tri naučnika su objasnili kako se kreću planete oko sunca?
Newton
"How do planets move? Kepler has told us. They go round the sun, and every planet follows its own line called the orbit. A planet's orbit never changes, but it is not a true circle. The orbit's shape is like an egg."
"We also know two things about their speed. First, every planet moves at a different speed. Second, every planet will change its speed when it passes near a fellow planet"
Kepler je objasnio orbitu planeta. Njutn je objasnio promenu brzine rotacije
Every planet has its own force of gravity. So every planet will try to pull its fellows, if they come near enough. For example, Mercury goes round the sun in 88 dana, and Venus goes round in 224 days. So Mercury must catch up Venus and pass her."
Njutn je posmatrao orbite Venere i Merkura i zapazio dve stvari
"While Mercury was catching up Venus, their speed changed, His grew faster and hers grew slower. After Mercury passed Venus, their speeds changed again. His grew slower, and hers grew faster.
What was happening? The planet in front was always pulling forward, and the planet behind was always pulling back."
Galileo
"We often see Venus and Mercury near the sun, in the evening or early morning. Also we can see clearly that they go round the sun. The telescope shows us that they change their shape, like the moon. When they're on this side of the sun, their shape won't be round. Why? Because the sun only shines on their faces, and we are behind their backs".
"When they are on the far side of the sun, they'll be round. But they'll also be smaller, because they are much farther. Venus is the nearest planet, so it also gives the brightest light."
One planet gave Galileo a lot of trouble. It was Saturn. In July 1610 he saw two large moons beside it. Next year they were much smaller. In 1612 there was not any sign of them. In 1613 they appeared again. In 1616 they almost formed a circle round it. Then they bagan to get smaller again.
"I need a stronger telescope", said Galileo