Our universe

The Moon THE MOONS IS THE EARTH’S only natural satellite. It is relatively large for a moon, with a diameter of about 3,470 kilometres-just over a quarter that of the Earth. The moon takes the same time to rotate on its axis as it takes to the earth(27.3 days), and so the same side (the near side) always faces us. However, the amount of the surface we can see-the phase of the moon-depends on how much of the near side is in sunlight. The moon is dry and barren, with negligible atmosphere and water. It consists mainly of solid rock, although its core may contain molten rock or iron. The surface is dusty, with highland covered in craters caused by meteorite impacts, to form dark areas called maria or “seas”. Maria occur mainly on the near side, which has a thinner crust than the fat side. Many of the craters are rimmed by mountain ranges that form the crater walls and can be thousands of metres high.

Mars Mars, know as the red planet, id the fourth planet from the sun and the outermost rocky planet. In the 19 th century, astronomers first observed what were thought to be sings of life on the mars. These singes included apparent canal-like lines on the surface, and dark patches that were thought to be vegetation. It is now known that the “canals” are an optical illusion, and the dark patches are areas where the red dust that covers most of the planet has been blown away. The fine dust particles are often whipped up by winds into dust storms that occasionally obscure almost all the surface. Residual fine dust in the atmosphere gives the Martian sky a pinkish hue. The northern hemisphere of Mars has many large plains formed of solidified volcanic lava, whereas the southern hemisphere has many craters and large impact basins. There are also several hung, extinct volcanoes, including Olympus Mons, Which, at 600 kilometres across and 25 kilometres high, is the largest known volcano ...

            The milky way The milky way is the name given to earth band of light that stretches across the night sky. This light comes from stars and nebulae in our galaxy, known as milky way galaxy or simply as “the galaxy”. The galaxy is believed to be a barred spiral, with a dense central bar of stars encircled by four arms spiraling outwards and surrounded by a less dense halo. We cannot see the spiral shape because the Solar  system is one of the spiral arms, the Orion arm (also called local arm). From our position, the center of the galaxy is completely obscured by dust clouds; as a result, optical maps give only a limited view of galaxy.                                            OVERVIEW OUR GALAXY                                   ...

Nebulae and star clusters A nebula is of dust and gas inside a galaxy. Nebulae become visible if the gas glows, or if the cloud reflects starlight or obscures light when it is stimulated by radiation from hot young stars. Reflection nebula shine because their dust reflects light from in around nebula. Dark nebulae appear as silhouettes because they block out light from shining nebula or stars behind them. Tow types of nebula are associated with dying stars; planetary nebula and supernova remnants. Both consist of expanding of gas that were once the outer layers of star. A planetary nebula is a gas shell drifting away from a dying stellar core. A supernova remnant is a gas shell moving away from a stellar core at great speed following a violent explosion called supernova.  Stars are  often found in groups known as clusters. Open clusters are loose groups of a few thousand young stars that were born from the same cloud and are drifting apart. Globular clusters are densely pac...

our universe Nobody   knows how big the Universe is, but astronomers estimate that it contains at least 125 billion galaxies, each comprising an average of 100 billion stars. The most widely accepted theory about the origin of the Universe is the Big Bang explosion_ that took place between 10 and 20 billion years ago. The Universe initially consisted of a very hot, dense fireball of expanding, cooling gas. After about one million years, the gas began to condense into localized clumps called protogalaxies. During the next five billion years, the protogalaxies continued condensing, forming galaxies in which stares were being born. Today, billions of years later, the Universe as a whole is still expanding, although there are localized areas in which objects are held together by gravity; for example, many galaxies are found in clusters. The big bang theory is supported by the discovery of faint, cool background radiation coming evenly from all directions.