What planets do we have? And what else can we find on the night sky?

Planets What is a planet? In Greek “planet” means a hiker – actually, planets wander through the sky (puzzle). How do they wander? It took quite a lot time for scientists to explain the rules of movement of the stars.

Acient times In acient times many people tried to solve this problem. One of them was Ptolemeo (2nd century A.D.) who developed so-called geocentric theory of the universe, in which planets as well as the Sun and the Moon go around the Earth making cirlces. Planets

Middle Ages That system, developed continuously, lasted to Copernicus ( ) who had an idea that it is the Sun which is in the centre of the universe. The rest of the planets (including the Earth) were to go around the Sun making circles. Unfortunately, his theory had big problems in foreseeing positions of the planets and few people believed it was true. But it started systematic research and discussion among the astronomers. Planets

The most important step in understanding movement of the planets was change those circles to ovals (elipses). That was made by J. Kepler in the beginning of the 17 th century. He come up with 3 rules which explain that movement. But it was Isaac Newton who explained those rules with his ideas of force, acceleration and gravity. Planets

Mercury This the first planet from the Sun, approximately 3 times nearer than the Earth. So it is really hot during the day, even 430 Centigrades (800 degrees of Faranheit)! However, during the night it is freezingly cold: -180°C (-300°F) Mercury has no air, so that its surface is covered with craters and reasembles our Moon. Mercury is one of the smallest planets, with mass only 1/18 of Earths. Beacause it is very close to the Sun, we won't be able to see it.

Venus It is quite similar to the Earth, but it is covered with clouds. So it is extreamly hot, even hotter than Mercury: +480ºC (900ºF) Clouds on Venus are very bright. It is also the closest planet to ours, so one can find Venus on the sky very easily. It happens that Venus goes in front of the Sun. It looks like a small dot. That will occur again in Now one can see Venus just before sunrise.

A foto from 2004 of Venus in front of the Sun.

Mars It is covered with rust, so it's called the Red Planet. Red is assiociated with blood, so it was devoted to the god of war. Long ago, water was flowing on its surface and made canyons which are the biggest known. Also, there are very strong hurricanes. Moreover, it has its own volcanoes, the biggest of which is 26km (16 miles) high. Mars has 2 small moons, Phobos and Deimos, which mean Terror and Fear

Mars The Red Planet

Jupiter Jupiter is the biggest planet in the Solar System. It has more than 300 times bigger mass than the Earth. In contrast to the previous planets, it is a huge ball of gases. Jupiter has 4 bigger and about 60 smaller moons. Those bigger were discovered by Galileo and named by Jupiter's lovers: sulfur-covered Io, icy Europe, Callisto and Ganimedes which is even bigger than Mercury!

Jupiter

Saturn This is the last planet visible by a naked eye. It is 10 times further than Earth and so it is much cooler with temperature of -150ºC (-240ºF) It is also less dense than water, so in very very big ocean it would float! Saturnus is widely known for its huge rings. But its moons are interesting as well. One of them, Titan, is even bigger than Mercury and owns atmosphere! Saturn and its family is being investigated by Cassini probe.

Uranus & Neptune They are much smaller than Jupiter and Saturn. Because they are made of methane they are all blue. Uranus lies on its side. You can imagine that by rolling on the orbit. Scientists observed the biggest hurricanes in whole Solar System with winds coming up to 2000 km/h (1250 mph). That's much more than speed of sound in the air!

Neptune

Pluto It is the last and smallest known planet. It has a relatively big Charon. They are both as big (or small) as the USA. In the beginning of this year scientists acknowlegded the discovery of two new moons of the Pluto.

Useful sites on the Internet: - news, knowledge and fun - if you know to how observe Iridum flashes or ISS passes - find out the beautiful photos of the stars made by Hubble Space Telescope

Thanks for your attention