Hello fellow aspiring astronomers! Have you ever heard the quote,
"That's one small step for man, one giant leap for mankind".
The famous astronaut Neil Armstrong said this in 1969 when he took his first step on the moon.
That quote makes me think about our lesson for today. Each step that scientists, mathematicians,
and philosophers took throughout history to learn more about space led us to where we are today. And
thanks to the hard work of astronomers, are leading us to where we will be going in the
future. Today we are going to explore the history of astronomy and those who studied it, describe
the early models of our solar system and discussed how we have established our current knowledge of
space, and Earth's place in the universe. So let's buckle up because this spaceship is ready to go!
Welcome back my fellow Space Explorers! Before we start talking about astronomers,
let's take a minute to talk about our solar system. So what is the solar system? Well, it's
the Sun and other celestial bodies or things in space that are in its orbit and revolve around it.
Eight giant planets, including the Earth, smaller dwarf planets, and millions of pieces of rocks and
Ice orbit our sun. Moons can also be found within the solar system. They are held in orbit around
planets by gravity. So how do we come to know all of this? Well, we have to go back to the year 384
BCE. That's over 2,400 years ago. This is when Aristotle was born. He was a Greek philosopher
who thought the Earth was the center of all things. His model of space placed to the Moon,
Sun, other planets, and stars all orbiting Earth. He thought that if Earth went around the Sun,
then the relative positions of the Stars would change as Earth moved. Aristotle thought that
Earth did not move. This may seem silly now but there were no telescopes when Aristotle lived.
He and other scientists looked for a parallax or a shift in the positions of celestial bodies
when they stood at different points on Earth but, they could not see any change. But this
is because the stars are so far away from Earth that you can only see Parallax with a telescope.
Maybe you have already heard of Aristotle but what about Aristarchus? Born 74 years later,
he was not a Greek philosopher. He was, however, a Greek astronomer and mathematician. He first
proposed a heliocentric model of the solar system. You know a model of the solar system
with the sun in the center. But believe it or not, hardly anyone believed him.
Come on people, now let's jump to the year 100 CE on Egypt's Mediterranean Coast. Ptolemy a
mathematician and geographer studied astronomy and wrote a famous book called 'Alma'. Just
this book was based on 800 years of observations of the planets. He used these observations to
develop a geocentric model or a model with Earth at the center that was used by other
astronomers for 14 centuries. Ptolemy believed that planets moved in small circles and they
all moved in bigger circles around Earth and well, it's a lot of circles. Since astronomers
followed Ptolemy's model for such a long time, we can jump ahead to the year 1508 CE.
This is when Nicholas Copernicus developed his own model of a heliocentric planetary system. Meaning
that he believed like Aristarchus; that the sun was the center of our solar system. However,
because astronomers still had no special equipment to observe outer space, Copernicus kept Ptolemy's
idea that planets moved in perfect circles. This is called "The Wheels, On Wheels system".
Even though he didn't have it all right, the heliocentric model of Copernicus is
generally seen as the first modern model of the solar system. To be developed
a few years later in 1605 CE, Johannes Kepler, a German mathematician, and astronomer carefully
analyzed the recorded observations of the planets and realized that the planets did not move in a
circular motion. They moved in ellipses with the sun in the center. Okay so now that we
have two important facts straight, the planets orbit around the Sun and they move in ellipses,
let's talk about a very important guy Galileo. An Italian astronomer, physicist, and engineer
who lived around the same time as Kepler. From the 17th century onward, Galileo has been seen
by many as the hero of modern science. Part of why he's so important to astronomers in particular is
that he improved the newly invented telescope. Using the telescope, he was the first to report
observations of the mountains on our moon, the moons of Jupiter, the faces of Venus, and the
rings of Saturn. He also studied gravity and some other pretty awesome science that we will cover in
future lessons. All of these discoveries and more helped to finally propel us into the modern era of
astronomy. Now we understand that the solar system is heliocentric with all the planets
and moons within it orbiting around the sun on elliptical paths. And although we've learned a
lot since the days of Aristotle and Aristarchus, over 2000 years ago we'd never have gotten here
without the ability to build on those earliest scientific discoveries and theories. We've come to
the end of our lesson for today. But, if you found this topic interesting, investigate to learn more,
and don't forget to check out the engaging games and thought-provoking resources related to this
lesson. And always remember in astronomy as in life you are out of this world!