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Welcome to the Solar System
Transcript of Welcome to the Solar System
The Sun is our nearest star. The Sun provides us with light and heat. It also gives out dangerous ultraviolet light which causes sunburn and may cause cancer. Without the Sun there would be no daylight, and our planet would simply be a dark, frozen world, with no oceans of liquid water and no life.
This huge ball of superhot gas is 1.4 million kilometres across, equal to 109 Earths set side by side. With a mass of 2 million-trillion-trillion-trillion kilograms, it weighs as much as 330 000 Earths. About 1 300 000 Earths would fit inside the Sun.
Although it seems small when seen at sunrise or sunset, this is only because the Sun lies about 150 million km away from us. At this distance, it takes about 8 minutes for sunlight to reach us – even when it is travelling at about 300 000 km/s. This means that we see the Sun set eight minutes after the event has actually taken place!
The Solar System.....
We live in one of the arms of a large spiral galaxy called the Milky Way. The Sun and its planets (including Earth) lie in this quiet part of the galaxy, about half way out from the centre.
The Solar System?
Named after the winged messenger of the gods, the planet speeds around the Sun once every 88 days. However, it spins on its axis very slowly – once every 58.6 days. Mercury is a small, rocky world. It is only about as wide as the Atlantic Ocean and 18 Mercurys would fit inside the Earth.
Mercury is very like the Moon. Its surface is covered with impact craters. It has no atmosphere and no water. The noon temperature at the equator can soar to 450°C but the nights are extremely cold, below -180°C. There may be some water ice in the deep, dark craters near the poles.
Venus is the second planet from the Sun, so it is always fairly close to the Sun in the sky.
It appears as a brilliant morning or evening “star” – the brightest object in the night sky apart from the Moon. Venus is so bright because it is covered by clouds that reflect much of the incoming sunlight.
In some ways, Venus is Earth’s twin. It is about the same size and made of the same rocky materials. It also comes closer to us than any other planet. However, it is blanketed with a thick atmosphere of carbon dioxide – the gas that we breathe out.
The carbon dioxide traps most of the heat from the Sun. The cloud layers also act as a blanket. The result is a “runaway greenhouse effect” that has caused the planet’s temperature to soar to 465°C, hot enough to melt lead. This means that Venus is even hotter than Mercury.
Without special protection, a visitor to Venus would die instantly – crushed by the immense air pressure, suffocated by the atmosphere, burned to a crisp by the scorching heat, and dissolved by the acid.
Earth is like no other planet that we have yet observed. It is the only world we know that has large areas of surface water and a lot of oxygen in its atmosphere. It is also the only world known to support life. This makes it very special.
Seen from spacecraft or from the Moon, the Earth appears as a blue planet – an oasis in space. This is because about seven tenths of its surface is covered by oceans. When the water is heated by the Sun, it changes to a gas (known as water vapour). If this gas is cooled, it turns back to water droplets, forming clouds and rain. This water cycle is made possible because Earth lies 150 million km from the Sun, in the 'Goldilocks' zone of the Solar System.
What does it mean to be in the Goldilocks Zone???
As the third planet from the Sun,
Earth is neither too hot nor too cold for oceans to exist. The temperature is also just right for life. And it has stayed that way for billions of years.
Mars is often called the 'Red Planet' because it appears in the sky as an orange-red star. The colour caused the ancient Greeks and Romans to name it after their god of war. Today, thanks to visiting spacecraft, we know that the planet's appearance is due to rust in the Martian rocks.
Mars is the fourth planet from the Sun. The average temperature is 63 degrees Celsius below zero - similar to winters in Antarctica.
The air is 100 times thinner than on Earth, and mostly made up of carbon dioxide. Human explorers will have to wear oxygen masks and special suits.
Violent storms can whip up clouds of dust. Sometimes these spread rapidly around the entire planet, hiding the surface from view.
Jupiter is the fifth planet from the Sun. Everything about Jupiter is large. It is so big that it could easily swallow all of the other planets (or more than 1,300 Earths). It also weighs more than twice as much as all the other planets. Despite its huge size, Jupiter is the fastest-spinning planet, rotating once in less than 10 hours.
Jupiter is a giant ball of gas, with no solid surface. It is mainly made of the very light gases, hydrogen and helium. The largest feature – called the Great Red Spot – is a giant storm, several times the size of the Earth. It has been blowing non-stop for more than 300 years.
Jupiter has a faint ring of dust, over 100,000 km wide. It is orbited by the largest family of satellites (63 at the latest count).
Saturn is the sixth planet from the Sun. It was thought to be the furthest of the planets until the telescope was invented.
Saturn is made mainly of the light gases hydrogen and helium. 764 Earths would fit inside Saturn, but the gas giant weighs only 95 times as much as our rocky world. If you could put all of the planets in a pool of water, Saturn is the only one that would float.
In a telescope, Saturn appears a pale yellow colour. It has no solid surface, so what we are seeing are clouds that appear as light and dark bands. These clouds are blown along by very strong winds. Above the cloud tops is a flat, disk-shaped system of rings.
Saturn has 31 known moons – more than any other planet except Jupiter. One of them, Titan, is planet-sized, but the others are much smaller.
Uranus is the seventh planet from the Sun. It was discovered by William Herschel in 1781. It moves quite slowly and has a long way to travel, so each orbit lasts 84 years.
Uranus is a giant world, the third largest planet in our Solar System. 64 Earths would fit inside it. Despite its size, it spins rapidly. A day on Uranus lasts only 17 hours 14 minutes. Uranus spins like a top knocked over on its side.
Uranus has 27 known moons. None of these are very big. The largest satellites are Oberon and Titania, both more than 1,500 km in diameter.
Neptune was discovered in 1846 and turned out to be almost an identical twin of Uranus. It is 57 times bigger than the Earth, but spins quite rapidly – one day lasts only 16 hours 7 minutes. One year on Neptune lasts for almost 165 Earth years.
Its interior is made of ices, with a possible rocky core. Although the atmosphere is very cold (-220 degrees C), the blue planet has some very strong winds and violent storms.
Neptune has at least five dark, narrow rings. It has 13 known moons. By far the largest is Triton, an icy world that is bigger than Pluto.
Pluto was discovered in 1930 by 24 year-old Clyde Tombaugh, who was using a special machine to compare photos of the sky. It turned out to be a tiny world, even smaller than our Moon.
Very little is known about Pluto. Its surface is extremely cold (-230 degrees C) and seems to be covered with frozen ices. One orbit lasts 248 years, no one born on Pluto would ever experience a single birthday!
For many years, Pluto was accepted as the ninth planet from the Sun (even though it sometimes comes closer than Neptune). Today, it is regarded as a “ dwarf planet”.
The Milky Way is shaped like a huge whirlpool that rotates once every 200 million years. It is made up of at least 100 billion stars, as well as dust and gas. It is so big that light takes 100 000 years to cross from one side to the other.
Astronomers have taken lots of beautiful images of galaxies in the Universe, but we don’t have a single photo of our own galaxy, the Milky Way.... why not???
The Moon is the Earth’s only natural satellite and was formed 4.6 billion years ago around some 30–50 million years after the formation of the solar system. It is the fifth largest moon in the Solar System and it orbits the Earth every 27.3 days.
The Milky Way...
The Solar System is made up of all the planets that orbit our Sun. In addition to planets, the Solar System also consists of moons, comets, asteroids, minor planets, and dust and gas.
That’s because no astronaut or man-made spacecraft has ever left the Milky Way in order to be able to turn around and take a picture of our home galaxy.
But astronomers still have a good idea about what the Milky Way looks like: a spiral shape with a centre that is slightly stretched out. We only see the Milky Way’s shape as a thin strip across the night sky, rather than as a spiral, because we are living within it and looking at it sideways.
In the grand scheme of things, we are smaller than
a grain of sand...