He observed that at midday there was a shadow in Alexandria, so he concluded that the earth is curved. In the third century BCE, Eratosthenes worked out that the earth was a sphere by observing shadows in Syene while reading a papyrus scroll one day.Įratosthenes experimented with the sun and sticks. Around 2,000 years ago, scientists were already investigating its nature and learning that it was not flat or infinite. Humans have known about the earth’s basic physical properties for a long time. That’s a lot of planets for us to be so insignificant. If you do the math, you’ll realize that our planet is one of 10 22 planets in the universe. Each galaxy contains billions or trillions of stars, and each star may have planets in orbit around it. The universe has a very large number of galaxies. It’s about 6 trillion miles or 10 trillion kilometers! That’s how far light travels during one year. It travels 186,000 miles per second or 300,000 kilometers per second, which means that it can go around the earth seven times in a single second.īecause of that, scientists measure the distance between stars in light years. Light is the fastest thing in the universe. That’s so big that we had to create a special unit of measurement for it. Compared to the universe as a whole, though, our world is just a speck of dust within another speck of dust. Our entire history is on this planet, and we consider it everything because of its size. Humankind has long been confined to the earth.
This book contains a whole bunch of interesting facts about aliens, Greek philosophers and Einstein’s thought experiments. That’s why I’ve collected some key points from Carl Sagan’s lectures on space exploration history that will allow others to learn about our place in the universe without getting bogged down by boring math or complex scientific concepts. It can be fun and interesting if you know what you’re talking about and are able to present it in an engaging way.
A lot of people don’t understand science, but it doesn’t have to be complicated. He made difficult things relatable to the masses, and that’s why he was so successful. Sometimes it feels as if your entire world is falling apart, but there are billions of people in the world, and the earth itself isn’t that important in comparison to everything else out there.Ĭarl Sagan was a great communicator. Sometimes life can be difficult and overwhelming.
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