Cosmos-Part 1
𧨠Impression:
Carl Sagan is one of the people who have inspired me since childhood. I remember feeling wonder at his pale blue dot quote. That everyone we have ever known and loved has lived their entire lives on a blue rock flaoting in nothingness. I am reading his book Cosmos right now. Following are some of the things that stuck with me.
âď¸Favorite Quotes:
The Cosmos is all that is or ever was or ever will be.
Until we find more intelligent beings elsewhere, we ourselves are the most spectacular of all the transformations-the remote descendants of the Big Bang, dedicated to understanding and further transforming the cosmos from which we spring.
We are like butterflies who flutter for a day and think it is forever.
But God became for him more than a divine wrath craving propitiation. Keplerâs God was the creative power of the cosmos.
đCambrian Explosion:
Simple life started on Earth not too late after there were oceans covering our planet. These organisms started to reproduce and multiply. They thrived in the vastness of the ocean. For billions of years, these were the inhabitants of our planet. They help change the atmosphere of the Earth to what we see today; Nitrogen and Oxygen make up 99% of the air around you.
Things changed suddenly about 540 million years ago. The reason why exactly it happened is not clear. The Cambrian explosion saw all sorts of complex animals appear. It was almost like The Earth was in a process of getting ready for complex life to appear until then. The Cambrian period lasted for about 55 million years the start of which is also referred to as the Big Bang of Biology.
đŞWanderers in the Sky:
The science of astronomy is as old as humanity itself. Astronomy was a way to keep records in the old days, which made it empirical science. Our ancestors used to tell time by looking at the position of the sun in the sky. The constellations changed during the year. They could be used as markers of changing seasons. When we discovered agriculture, these constellations told us the best times to sow and reap our crops.
Most of the stars in the night sky were fixed in their place. However, there were some âstarsâ that would move across the night sky. They would leave and join constellations. The wanderers in the heavens. We now know that these were the planets in our solar system. The word planet comes from ancient Greek and it means wanderer.
Fast Forward to the Early seventeenth century, scientists such as Copernicus, Galileo, and Kepler were working on how the planets in the sky move. The popular model backed by the church put the Earth in the center of the universe with the sun and the other planets revolving around our home. Copernicus was the first one to propose a heliocentric model. He saw a universe where the Sun was at the center and the Earth along with the other 5 planets; Mercury, Venus, Mars, Jupiter, and Saturn (Uranus, Neptune, and Pluto were not discovered yet) revolved around it. In 1610, Galileo discovered Jupiterâs Big four moons; Io, Ganymede, Europa, and Callisto. Galilean moons revolved around Jupiter. This was the first proof that not everything in the universe has to revolve around The Earth.
Johannes Kepler, around the same time as Galileo discovered Jupiterâs moons, came up with a theory about how the planets move around the Sun. Following are Keplerâs three laws of planetary motion:
First Law: Planets move in elliptical orbits with the Sun as a focus.
People at the time thought that the movement of the planets in the night sky was perfect. Even Kepler initially believed that the planets revolved around the sun in perfectly circular orbits. The observations suggested otherwise. This was one of the first steps in understanding that the planets were not flawless and were actually made of the stuff that the Earth was.
Second Law: A planet covers the same area of space in the same amount of time no matter where it is in its orbit.
This one is more mathematical. Consider a planet orbiting the sun in an ellipse as shown in the figure. When the planet is closer to the sun, it moves faster than when it is farther away. The arc length from a to b is long but the distance between the sun and the planet is small. On the other hand, the arc length from c to d is small, but the distance is large. The area traced in both cases is equal; area abs is equal to area cds. This will hold true anywhere in the orbit.
Third Law: A planetâs orbital period is proportional to the size of its orbit (its semi-major axis)
In English, this means that the time a planet takes to orbit the Sun is directly proportional to its distance from the sun. The closer the planet is to the sun the faster it will complete one cycle and vice versa. Mathmatically speaking, the square of the time (in Earth years) it takes for a planet to go around the sun is equal to the cube of the distance between the planet and the sun( in AUs). One Astronomical is the distance between Sun and The Earth. For example, Saturn is 5.2 AUs away and it takes 12 Earth years for it to complete one revolution around the sun. This law holds not only for planets but also for other bodies like asteroids and comets.
Keplerâs laws beautifully explain how the bodies in our solar system move. However, these laws do not explain why the planets move this wat. Kepler, in his work, pondered that there is some force like magnetism that keeps the planets in orbit. Later in the seventeenth century, some English fellow named Issac Newton would come along and discover that the same force by which the apple falls to the ground keeps the planets in orbit.
âď¸The Tuskunga event:
The Tuskunga event happened on June 30, 1908. There are some captivating testimonies of people who witnessed this event. They describe seeing the sky split in half and catch fire. After some time, a loud boom was heard followed by rumbling and a shock wave (it traveled the Earth twice). Luckily, ground zero was far away from civilization, deep into a forest, so there are no confirmed deaths. The event threw dust into the sky. So much so that you could comfortably read a book at night because of the scattered light from a city far away.
Scientists theorized that the Tuskunga event was caused by a meteor colliding with the Earth. In 1927, soviet meteorologist Leonid Kulik led a research expedition to investigate ground zero. He believed that they would find a crater caused by the meteor impact. After a gruesome journey, they reached the impact site. The trees were burned up and they faced radially away from the center, but there was no crater. How could there be all these signs of an impact and still no crater?
The best theory now is that this was a comet and not a meteor. This comet did not hit the Earth, it flared up in the atmosphere some kilometers above the surface. Unlike meteors, comets are mostly made of ice, so it is easier for them to burn up. Although it came incredibly close, the comet was just small enough to not hit the earth.
