Chapter 2

1. Chapter 2 The Solar System

2. Solar System • Comprised of • Sun • Inner Terrestrial Planets (Mercury, Venus, Earth, Mars) • Main Asteroid Belt • Outer Gas Giants or Jovian planets (Jupiter, Saturn, Uranus, Neptune) • Pluto and the Kuiper Belt • Oort Cloud

3. Electromagnetic Radiation (Light) • Visible light, radio waves, infrared light, microwaves are all examples of electromagnetic radiation. • The type of electromagnetic radiation depends on the frequency. Visible light is the portion of the electromagnetic spectrum, between the frequencies of 7.5×1014 Hz and 3.8×1014 Hz.

4. Electromagnetic Radiation (Light) • The higher the frequency, the higher the energy of the electromagnetic radiation. Conversely, the longer the wavelength, the lower the energy of light (See Diagram). • Gamma rays and x-rays are very dangerous because of their high frequency and energy. The Earth’s electromagnetic field and atmosphere block radiation at those high frequencies thus protecting us from them. • Any frequencies of light that the Earth blocks must be studied from space.

5. Electromagnetic Radiation (Light) • Light simultaneously exhibits properties of both waves and particles. The particle is called a photon. • The speed of light (denoted classically as c) in a vacuum is exactly equal to 300,000,000 meters per second (186,000 miles per second).

6. The Sun • The Sun is a star. It is one of more than 100 billion stars in our galaxy. • It contains more than 99.8% of the total mass of the Solar System. • By mass, the Sun is, at present, about 70% hydrogen and 28% helium everything else ("metals") amounts to less than 2%. This changes slowly over time as the Sun converts hydrogen to helium in its core.

7. The Sun • All matter in the Sun is in the form of plasma due to its extreme temperature. • The surface of the Sun, called the photosphere, is at a temperature of about 5800 Kelvin (10,000 degrees F). • The corona, extends millions of miles into space but is visible only during a total solar eclipse. Temperatures in the corona are over 1,000,000 Kelvin.

8. The Sun • The Sun's energy output of 386 billion billion megawatts is produced by nuclear fusion reactions. (By comparison Hoover Dam produces 2,000 megawatts.) Each second about 700,000,000 tons of hydrogen are converted to about 695,000,000 tons of helium and energy in the form of gamma rays. As it travels out toward the surface, the energy is continuously absorbed and re-emitted at lower and lower temperatures so that by the time it reaches the surface, it is primarily visible light.

9. The Solar Wind • In addition to heat and light, the Sun also emits a stream of charged particles (mostly electrons and protons) known as the solar wind which travels throughout the solar system at about 450 km/sec. The exact composition of the solar wind has not yet been measured. A sample return mission, Genesis, returned to Earth in 2004 and is undergoing analysis, but it was damaged by crash-landing when its parachute failed to deploy on re-entry to Earth's atmosphere.

10. The Active Sun • Since it’s not a solid, the outer layers of the Sun exhibit different rates of rotation. At the equator the surface rotates once every 25.4 days; near the poles it's as much as 36 days. This differential rotation causes its magnetic field lines to become twisted together over time, causing magnetic field loops to erupt from the Sun's surface and trigger the formation of the Sun's dramatic sunspots and solar prominences.

11. The Active Sun • Sunspots are "cool" regions (they look dark only by comparison with the surrounding regions). Sunspots can be very large, as much as 50,000 km in diameter. The frequency of sunspots varies cyclically over a 22 year period with the magnetic poles switching every 11 years.

12. The Active Sun • Many solar prominences (closeup) break apart emitting a burst of plasma (protons and electrons). This is called a coronal mass ejection(CME). These expand away from the sun at supersonic speeds carrying up to 50 million tons of material.

13. The Active Sun • A solar flare is a violent explosion in the Sun's atmosphere with an energy equivalent to tens of millions of hydrogen bombs. The frequency of solar flares varies, from several per day when the Sun is particularly "active" to less than one each week when the Sun is "quiet". Solar flares may take several hours or even days to build up, but the actual flare takes only a matter of minutes to release its energy.

14. The Active Sun • CMEs, along with solar flares, can cause particularly strong polar auroras (northern and southern lights), can disrupt radio transmissions, cause power outages (blackouts) and damage satellites and electrical transmission lines. The radiation from the flares can give passengers in airplanes a dose of radiation equivalent to a medical X-ray • The radiation risk posed by solar flares and CMEs is one of the major concerns in discussions of manned missions to Mars. Some kind of physical or magnetic shielding will be required to protect the astronauts.

15. The Sun’s Future • The Sun is about 4.5 billion years old. Since its birth it has used up about half of the hydrogen in its core. It will continue to radiate "peacefully" for another 5 billion years or so (although its luminosity will approximately double in that time). It will then enter its red giant phase, expanding as the hydrogen fuel in the core is consumed and it starts to burn helium.

16. The Sun’s Future • Following this phase, giant thermal pulsations will cause the Sun to throw off its outer layers to form a planetary nebula. The Sun will subsequently become a white dwarf, slowly cooling over many more billions of years. Although commonplace by stellar standards, these events will likely result in the total destruction of the Earth.