The Earth and the sun and the other seven planets are isolated in space. This set of eight spheres that circles the bright sun is poised in emptiness1 and separated by unimaginable distances from everything else in the universe. Because the sun is its central figure, the family of bodies that accompanies it is called the solar system, which in its turn2 is a part of a galaxy and eventually of the Universe.
Until the 17th century the solar system was thought to consist of only five planets besides the earth and moon. In 1609, soon after having heard of the invention of the telescope in Holland, Galileo built one of his own and was able to add four new bodies to the system: the brighter of the moons (or satellites) that revolve around Jupiter. Since Galileo’s time telescopic improvements have made possible the discovery of many more members of the sun’s family.
It is common knowledge now that our neighborhood in space consists of our local star, the sun, and its family of eight planets, nearly 70 moons, millions of comets and countless asteroids. The mean diameter of the solar system is approximately 7 billion miles.
Dominating the entire solar system is the sun, which is nearly a thousand times more massive than all the planets put together. The energy the sun generates by nuclear fusion makes it luminous and provides the rest of the solar system with heat and light. Its gravity pull s the planets so that they move around it in almost circular orbits.
The list of planets now includes eight; in order from the Sun they are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. All planets are divided into two groups: four small rocky ones close to the sun and four big gassy ones farther out. All except Mercury and Venus have satellites.
Planets revolve around the sun and rotate on their axes. Nearly all the revolutions and rotations are in the same direction, but the rotation rate is different, slow with some planets, rapid with others. Only the rotation of Venus and the revolutions of a few satellites are in the opposite direction. Uranus is an exception of a different kind since it rotates about an axis only 80 from the plane of its orbit.
All the orbits except those of the comets lie nearly in the same plane. Planets stay on their orbits according to the law of universal gravity. All celestial bodies have an attraction of their own and pull each other. This force decreases sharply the greater the distance. At the same time the force of their movements tends to pull them away from each other. This interaction was discovered by the great British scientist Isaak Newton in the 17th century.
Astronomers have identified more than 4.000 pieces of rock, known as asteroids, orbiting the sun. However there are probably millions of these minor planets, some only a few metres across. Most are in the Asteroid Belts lying between Mars and Jupiter.
The farthest, Chiron, orbits the sun beyond Saturn.
The sight of a great comet hanging in the sky, looking like a ghostly dagger poised to strike3, is an impressive spectacle. Yet, comets are all snow and no substance – a “dirty snowball”, or lump of ice. The long, oval orbit of a comet carries it close to the sun and far away again. As it approaches the sun, the frozen surface starts to evaporate, forming a great head of gas, which the solar wind sweeps4 into a long tail. The comet’s moment of glory lasts a brief few weeks before it heads back to the icy outer reaches of the solar system.
Planets, asteroids and satellites are only visible by virtue5 of the sunlight they reflect. What we see of any of these objects at a particular time is limited to the half that faces the sun. Planets with orbits larger than that of the earth never come between us and the sun, so we can always see nearly the whole of their illuminated sides. Mercury and Venus, however, have orbits smaller than the earth’s and are between us and the sun for a good part6 of each revolution. In this position their dark sides are turned toward us, and we see them either not at all or as crescents.
Notes:
1. to be poised in emptiness – находиться в невесомости
2. in its turn – в свою очередь
3. a ghostly dagger poised to strike – призрачный кинжал занесенный для удара
4. to sweep – зд.: преобразовывать
5. by virtue of smth. – посредством чего-либо
6. a good part of smth. – значительная часть чего-либо
Word Study
Ex.1: a) Read correctly the names of the planets. Mind the stress.
| Mercury Venus Earth | Mars Jupiter Saturn | Uranus Neptune |
