Solar System.

People have been watching the sky for thousands of years and wondered exactly what is out there. With advances in telescopes as well as spaceships which have physically traveled to various planets, a considerable amount of knowledge has been obtained to better understand the universe near to us. The name of our system comes from the old latin word for the Sun: Sol. Because the Sun is the largest object in the system and all the other bodies orbit around it, it became known as the Solar system.

What is the Solar System?

At the center of the Solar System is the Sun. This is but one of billions of stars in the sky, but is important to us as it gives us warmth and energy for us to use. There are many worlds that are near the Sun, each of them are as different as you can possibly imagine. All of these worlds that either orbit the Sun or orbit a planet going around the Sun make up what we call the Solar System. As you read each of the sections about these different worlds, we will explore the differences between all of these worlds, and hopefully you will understand how unique and special the Earth is as well.

There are a total of nine planets in our system. The inner-most planet is called Mercury. This is followed by Venus and then our Earth. Beyond Earth is an orange-hued planet called Mars. In the outer part of the system are four giant planets called Jupiter, Saturn, Uranus, and Neptune. The outermost planet is a small world named Pluto.

Our system also includes many other bodies. The moons are small worlds that orbit the planets, in much the same way as the planets orbit the Sun. There are also a lot of much smaller objects called asteroids. These are big chunks of rock or metal that are mostly found orbiting the Sun between Mars and Jupiter. We also get visitors from the cold outer edge of our system that are called comets. These are big lumps of ice and dust. Comets can form immense tails when they come close to the Sun and start to melt.

The solar wind is a hot gas that erupts from the sun and flies away into space. This gas travels past the planets into outer space. The place where this gas reaches the very thin gas between the stars is at the edge of the solar system. This bubble of gas is about 100 times as far from us as the Earth is from the Sun. Beyond that is a lot of empty space. The nearest star to the Sun is thousands of times further away than the size of the entire Solar System. It's a very, very big universe out there.

Who discovered it?

Prior to 1781, there were only seven known bodies in our solar system, besides the Earth. These seven were the Sun, our Moon, Mercury, Venus, Mars, Jupiter, and Saturn. These had been known since humans first began to observe the sky at night. There were also visitors called comets that would appeared in the sky for a time, then fade away.

The Babylonians believed that each of these objects was related to a different deity, and their calendar used a seven-day week. The practice of naming the seven visible objects of the solar system still continues to this day. Each of the English words for the day of the week comes from an old name for a god or goddess. In English this is a mixture of both Norse and Roman gods, but in other languages the connection to the Roman names of the planets is more apparent.

Weekdays	Object	Related Norse Diety	Spanish equivalent
Sunday	Sun		Domingo
Monday	Moon		Lunes
Tuesday	Mars	Tyr	Martes
Wednesday	Mercury	Woden (also Odin)	Miércoles
Thursday	Jupiter	Thor	Jueves
Friday	Venus	Frige (also Freyr)	Viernes
Saturday	Saturn		Sábado

Galileo Galilei first turned a telescope on the sky and began to write down what he saw. Among the things he saw were four moons orbiting Jupiter. As time passed and the telescope was improved, more objects were found. In 1655, Christiaan Huygens discovered the moon Titan orbiting Saturn. In 1781 Sir William Herschel discovered the planet Uranus. In 1801, Giuseppe Piazzi discovered the first asteroid. Many more asteroids were later discovered by astronomers.

The discovery of the planet Neptune did not come by chance, but was found using math. Astronomers had made tables of where each body should appear in the future. But Uranus did not match the predictions. So a model was made to account for the difference. This model predicted that the gravity from an unknown planet was pulling on Uranus. The model also predicted about where the mystery planet would be found. This planet was then found in 1846. The last planet Pluto was later found in 1930 using the same method.

How was it formed?

Our Solar System is part of a much larger system called the Milky Way. This is a vast mix of dust, gas, stars, and other objects that is called a galaxy. Our galaxy rotates about the center, and if you could see it from a long, long way off it would look like a wispy pin-wheel.

Within our Milky Way galaxy are clouds of dust and gas where stars are born. Our Solar System was created in just such a cloud. A part of this cloud began to collapse under the pull of its own gravity. As it got smaller, it formed a big, spinning disk of gas and tiny particles of dust. This disk was thickest at the middle, and this part slowly collapsed to form the early Sun.

The remainder of the disk continued to rotate about the Sun in the center. The tiny particles of dust were now close enough so that they would often collide, and some of these would stick together. The bits of dust would slowly collect to form grains. These would in turn join to form lumps the size of gravel, then pebbles.

As the objects grew in size, a few grew larger than the rest and began to pull on the other rocks with their gravity. The rocks grew ever bigger, reaching the size of mountains which crashed together with powerful force. In the end there were only a few massive bodies left, which swept up the rest of the disk to form the planets, moons, and asteroids.

While this was going on, the Sun began to glow from the huge energy released by its own collapse. The temperature at the center of the Sun reached a million degrees, and it turned into a furnace that could create more energy by smashing tiny atoms together. This energy rose up to the surface and was emitted as light, heat, and other forms.

This energy being emitted by the Sun swept away any surviving tiny particles and gas from the inner Solar System, leaving behind only the larger objects.

What will happen to it?

About four thousand million years from now, the Sun will have used up most of fuel. It will begin to enter the final stages of its life. It will expand into a huge star called a Supergiant. The size of this star will be so big that several of its planets will be inside, including the Earth. These planets will be burnt to a crisp inside the very hot atmosphere.

Eventually the sun will begin to throw off its outer atmosphere, forming an immense sphere of faintly glowing gas that astronomers call a planetary nebula. The sun will then shrink down into a small star called a white dwarf. This will be about 100 times as small as the current sun we see. It will then slowly begin to cool and grow ever fainter over time.