We explore our position in space and discover what stars, planets, and moons really are.
What is up there?
As long as humans have lived, we have looked up at the night sky and wondered upon its inexplicable magnitude. Over the centuries, as the sun rose every morning and the moon rose most nights, it seemed obvious that the Earth and the people on it were the center of the universe.
The Milky Way
The Milky Way has fascinated us since the beginning of human civilization. On a cloudless night, one could see the entire galaxy across the sky.
The first telescope was invented in the late 1800s and allowed Galileo to see celestial bodies such as our moon much more clearly.
Orion and ancient beliefs
The ancient Greeks believed that the stars were the depictions of gods, put there to honor their wonderful deeds.
Comets and Shooting Stars
Bright comets have captured the attention of early civilization for millennia, as early as 3000 B.C.
It is thought that the universe began (before time and space existed) with one Big Bang 14 billion years ago. This explosion expanded so fast that in 1 minute it had grown to the size of one million billion miles and was still growing.
Although from our perspective the Earth seems like a really important place, the universe views it slightly differently. Our sun is only one of the billion trillion stars in the universe.
The Solar System
Our solar system consists of 8 planets that revolve around a common star: the sun. If the earth were the size of a pea, our solar system would still be more than 4 miles in diameter.
Star cluster is a group of stars.
The Milky Way Galaxy
The Milky Way is made up of billions of stars just like our own sun. Our closest star (that isn’t the sun) is 25.67 trillion miles away. So if the Milky Way galaxy was the size of North America, our solar system would be about the size of a coffee cup.
The Milky Way is part of a bigger galaxy called the Local Group and the Local Group galaxies are part of an even larger group of galaxy clusters called the Virgo cluster. Millions of galaxy clusters are strung together like an unimaginably gigantic spider web across the universe.
The universe we talk about is only the observable universe, that is, the parts of the universe that have emitted light that has traveled all the way to Earth. The actual universe is probably a lot larger than this.
How do we know what we know?
Before the invention of the telescope in 1608, the only planets we could see with the naked eye were Mercury, Venus, Mars, and Jupiter. But telescopes could not tell us everything, as our solar system is large and the universe is infinitely larger, so scientists had to use mathematics to create laws or theories based on the best evidence to explain phenomena in space.
Copernicus’ Heliocentric View
In the 1500s, Copernicus put forward that the sun, not the earth, was the center of our solar system.
Arguably one of the most amazing human accomplishments was stepping foot on the moon.
Voyager 1 and Voyager 2
These two deep space probes were launched in 1977 and have been providing us with valuable data ever since. They are the farthest human-made object from us.
The Hubble Space Telescope
Although telescopes are great for the average astronomer, the view through the telescope is distorted by the the Earth’s atmosphere. So, in 1990, the Hubble Space Telescope was launched. It floats outside our atmosphere, collecting a plethora of images.
Mars is our closest neighboring planet, the one that is most likely to sustain human life. Many robotic vehicles have been sent to Mars to explore the Martian world.
Life of a Star
It would be unimaginable to conceive the amount of stars that there are in the universe. It is estimated that the universe holds 100 billion galaxies and within each galaxy there are about 100 billion stars. It would be just as unimaginable to realize that stars, just like us, have a life cycle. They are born, mature, and die, over billions of years.
Cloud of Nebulae
Stars are luminous balls of mostly helium and hydrogen gas that start their life as nebulae, or large clouds of dust, clouds, and plasma.
The classification of a star depends on its size and in what stage of its life cycle or star cycle it is. When a star is born from a nebulae it is called a protostar.
Main Sequence Stars
As a protostar heats up and contracts, it becomes a main sequence star. These stars emit energy for billions of years, converting hydrogen to helium. Most stars we see are main sequence stars, meaning they are in the middle or main sequence of their lives.
When the hydrogen runs out, helium moves to the core of the star and causes the star to become extremely hot and expand, making it into a red giant.
This red giant then sheds it outside layer and cools off, becoming a white dwarf.
Finally, when it cools to darkness, it becomes a black dwarf. This is not considered a real star as we have never been able to see a black dwarf because it has died and it no longer emits light.
Our Star – the Sun
The sun is the closest star to us in the galaxy. A mere 93 million miles away, it has a temperature of 9,932 °F at its surface and 27 million °F at its core.
So far the sun has been around for 4.3 billion years and it has another 7 billion years to go until it becomes a black dwarf.
Our incredibly large sun
Not only is the sun hot, but its mass makes up 99.87% of the mass of our solar system and it is so big that we could pack 1 million Earths inside of it.
It's just a star
Although to us our sun is the giver of warmth, light, and life itself, it is just one of 100 billion stars in the Milky Way galaxy. A yellow dwarf star, our sun is a small main sequence star in the middle age of its life.
Our solar system – The Terrestrial planets
Over 4.6 billion years ago, a giant molecular cloud collapsed, creating our sun and the planets, comets, and asteroids that surround it. This is what we now call our solar system. A total of 8 planets orbit around the sun due to its immense gravity.
The first 4 planets, Mercury, Venus, Earth, and Mars, are said to be the terrestrial planets.
Mercury, our smallest planet, sits closest to the sun, with surface temperatures ranging from -280 °F to 840 °F.
These extreme temperatures are due to Mercury not having enough atmosphere to protect itself against the heat when it faces toward the sun and the cold when it faces away.
Venus, the second planet from the sun, is known as Earth’s sister as it is similar in size and mass to Earth. It is the hottest planet and contains the most volcanoes of any of the planets.
The Earth is the only planet that we know of that is hospitable to life. Mars has evidence that it may have supported life in the past but there is no evidence of life ever existing on Venus or Mars.
The Red Planet, Mars, our small neighbor on the other side, is only 15% the size of Earth yet holds the biggest volcano in space, Olympus Mons. At 16 miles high and 374 miles across, the volcano is roughly the size of France.
The Gas Giants and Ice Giants
The gas and ice giants are our 4 outer planets, with Jupiter and Saturn being our gas giants as they are big and made out of gas, and Uranus and Neptune being our ice giants, as they are big and made out of ice. Each of these giants can contain more than 10 Earths inside of them.
Jupiter is really, really big. If you were to take all the other planets and combine them, Jupiter would still be 2.5 times bigger than that. Even though it takes Jupiter 11.8 years to orbit the sun, it rotates exponentially fast and a day lasts 9 hours and 55 minutes.
Jupiter’s Red Spot, a storm that has raged for the last 350 years, is bigger than the Earth itself.
Saturn, our sixth planet orbits the sun every 29.4 years. Saturn has 150 moons and the most extensive rings in the atmosphere that stretch outward more than 75,000 miles. These rings may be long but they are really thin, only 12.5 miles.
Our seventh planet, Uranus, is the only planet that tilts at 98 degrees, causing it to rotate around the sun sideways. It reaches the coldest temperature out of our solar system, at -371 °F.
Neptune, the Blue Planet, was named after the Roman god of the sea. It sits 2,795 million miles from the sun and takes 164.70 years to make one full orbit. While it takes 8.3 minutes for the sun’s light to reach Earth, it takes 4 hours and 49 minutes for the sun’s light to reach Neptune.
When we look into the night sky, the most striking astrological body we see is our moon. However, this mass of rock is not unique in our universe as millions of other planets have moons. In our solar system alone, we have now found 336 moons.
The moon is 238,857 miles away and it actually regulates the Earth’s wobble on its axis, which contributes to our relatively stable climate over the last 4.5 billion years.
The Phases of the Moon
Our moon looks very bright at night but it holds no light of its own as the light we see is the sun reflecting off of it. Every night the moon displays itself in a slightly different shape depending on its relation to the Earth during its 27.4 day lunar cycle.
When the moon is between the sun and the Earth it looks like it is not there and we call it a new moon.