The Solar System A Solar System is made up of one or more stars which emit huge amounts of radiation (visible and invisible) and a number of smaller planets which orbit the stars and emit little or no radiation. The Age of our Solar System Astronomers think that our solar system formed about 5 billion years ago. Our Milky Way Galaxy is thought to have begun formation 13.7 billion years ago and our universe is thought to have formed billion years ago. Our Solar System Formation A nebula made up of mostly hydrogen and dust containing some heavier elements like carbon, oxygen, nitrogen and iron (from a former supernova explosion) began contracting and spinning. As the cloud spun it began to flatten into a disk and to heat due to gravity pressing it smaller. Our Solar System Formation Spinning caused particles to collide and to clump together. The lighter particles (ices) moved to the outside of the disk while the heavier particles moved towards the centre. As the clumps of particles grew is size their gravity also increased pulling more particles to them. These clumps became the planets. Our Solar System Formation When the centre of the disk reached a temperature of C, fusion began there and the sun was born. As the sun radiated light and heat energy as well as energetic particles from itself (solar wind), it pushed the remaining nebula out into space leaving the planets behind. A A Summary of the Birth of our Solar System. Rotations and Revolutions of the Planets The planets revolve about the sun in nearly the same flat plane (Pluto not a planet- orbits at an angle). All planets rotate or spin like tops in the same direction except Venus and Uranus. Rotations and Revolutions of the Planets Planets like Earth, Mars, Saturn and Neptune spin around a tilted axis which gives them different yearly seasons. Circles and Ellipses An ellipse is an oval which has two foci (special points used to construct an ellipse). A circle is really a special ellipse in which the two foci are in the same place, the centre. Planet Orbits : Ellipses with the sun on one focus The planets all orbit the sun in ellipses in which the sun is on one of the foci of the ellipse. The Sun The sun contains 99.86% of the mass of our solar system. It is composed mostly of hydrogen gas which makes other heavier elements like helium and lithium in its centre by the process of atomic fusion. Sun Composition The sun is made up of about 75% hydrogen, 23% helium and less than 2% oxygen, carbon, neon and iron. Its elements are in the fourth state, the plasma state, a gas-like state in which many particles are charged causing the plasma to respond to magnetic fields. The suns core is 150 times as dense as water. Sun Statistics The diameter of the sun is km. On average, the sun is km from earth. It takes 8 min 19 sec for light to reach earth from the sun. The suns core is at C, its surface is at 5,500 C and its outer atmosphere is at C. Sun Structure The centre or core of the sun fuses hydrogen into heavier elements at a temperature of C. The thin outer layer, the photosphere at 5500 C emits photons of light. The inner sun atmosphere layer, the chromosphere at C is at times penetrated by loops called solar prominences and outward bursts called solar flares which release huge bursts of particles into space. Sun Structure The outer sun atmosphere layer at C is called the corona. Bursts of energetic gases into the corona spew out high energy particles into space called solar wind. Solar wind particles which would kill life on earth are deflected by the magnetic field of the earth. The Northern Lights The earths magnetic field called the magnetosphere deflects solar wind away from the earth. Some of the solar wind particles get trapped at the north and south poles and as they slowly penetrate down to the upper atmosphere layers, these particles give off energy in the form of light which is referred to as the Northern (Southern) lights. Sunspots Sunspots are cooler regions on the photosphere associated with strong magnetic activity. Eventually they usually erupt into solar prominences. The number of sunspots usually rises and falls in an 11 year cycle. High sunspot activity is associated with higher temperatures on earth. In the 1600s the sunspot activity dropped dramatically for a few decades and this produced a little ice age on earth with lower summer temperatures, colder winters and advancing glaciers. The Sun Supports Life and Makes Our Weather All living things get their energy to live from their food which ultimately comes from plants. Plants store sunlight energy in their parts using the process of photosynthesis. The sun also heats the earth causing clouds, winds, rain, tornadoes, hurricanes our weather. The sun makes life possible on earth. The Sun: Our Extinguisher Formed about 4.6 billion years ago, the sun is increasing in brightness and energy level about 10% every billion years. Astronomers estimate that in 1 billion years from now, the earth will be too hot for liquid water to exist which will be the end of all life on planet earth. 5 billion years from now the sun will become a red giant expanding outward to scorch the dried-up earth. The Astronomical Unit (AU) One astronomical unit is the average distance that earth is from the sun (1 AU = km). Astronomical units are used to measure the large distances between planets in our solar system. Jupiter is 5.27 AUs from the sun. Inner and Outer Planet Differences The inner terrestrial planets (Mercury, Venus, Earth and Mars) are rock-like with higher densities while the outer gas giant planets (Jupiter, Saturn, Neptune and Uranus) are composed of ices and gases that have much lower densities. Planetary Density and Size Differences The gas giant planets are large with low densities (not tightly packed) they almost became stars. The terrestrial planets are much smaller with much higher densities.