ASTR 1514 1st Edition Exam #3 Study Guide Chapter: 9-12Chapter 91.) What is the difference between a planet and a dwarf planet?Planets- An object that orbits the sun- Large enough to pull themselves into a round shape- Large enough to clear area around their orbitsDwarf Planets- Object that orbits the sun- Large enough to pull themselves into a round shape- NOT large enough to clear area around their orbitsPluto is different from other Outer Solar System Planets because:- It has a very elliptical orbit, e = 0.25- Can actually be closer to the Sun than Neptune at times (important because Pluto is mainly further away from the Sun than Neptune)- Very low mass – 1.3x1022- Very high inclination orbit: 17 degrees- Other outer solar system planets are much larger- It’s moon, Charon, is very large compared with Pluto. 2.) Craters and bright/dark areas reveal geological activity on moons- Such as: Geysers and Volcanoes- Few Craters due to resurfacing- Our moon may have been geologically active in the past (Evidence are the Maria)3.) Jupiter’s moon, Io, is the most volcanically active object in the solar system.- No crater mean is has a young surface- It experiences Tidal forces- The stretching of a planet due to gravitational pull of surrounding objects- Orbit is non-circular, mainly due to Jupiter’s other large moons (Europa, Ganymede, Calisto) all of which experience orbital resonance - The gravitational pull of these moon on to Io stretches it causing it to heat up and gain it’senergy for volcanic activity, resurfacing. - Galilean moons are less geologically active the further they are from Jupiter4.) Asteroids- Relics of planetisimals – small bodies formed when the solar system formed- Mostly found in the asteroid belt between Mars and Jupiter- Jupiter’s Large mass prevented a planet from forming between Jupiter and Mars5.) Comets- Have very eccentric orbits- May be the source of water on Earth- Small icy bodies from the Kuiper belt, the scattered disk, or the Oort cloud, that entered the inner solar system- Become active when close to the sun- Sun heats comet, vaporizing and causing three effects- 1.) Coma (head), 2.) Ion tail and 3.) The dust tail. 6.)Meteoroids- A small object that would become a meteor if it entered Earth’s atmosphereMeteor- Small object falling through Earth’s atmosphere, glowing due to heating by Earth’s atmosphereMeteorite- A remnant of a meteor that makes it to Earth’s surface- Can be used to date the age of the Solar System- Can be found where there are few rocks, places such as; Antarctica, Australian Desert, and the Sahara. 7.) Astronomical Parallax (surveyor’s method)- Parallax: The change in the apparent position of an object caused by a change in the position of the observer- Measure baseline distance between the Earth at two points in its orbit then measure the angle to the star- This method only works for measuring closer stars, because further stars will not have an apparent change in motion- Angle is measured in parsecs, 1 parsec = 3.26 light years. - The greater the parallax the smaller the distance8.)Brightness – The apparent property – how much total energy an object appears to emit, depends on the distance. Further away objects appear less bright. (Ex: A street full of street-lights, every light emits the same energy but further away lights appear less bright)Luminosity – An intrinsic property – much TOTAL energy an object emits, does NOT depend on distance. Brightness is measured in Magnitudes, visible stars are measured in 6 categories. Brighter stars have a Lower magnitude. Apparent Magnitude (m) – brightness- depends on how bright a star appearsAbsolute Magnitude (M) – Luminosity - How bright the star would be at a distance of 10 parsecs from us. 9.) Two methods to measure the temperature of a star1. Shape of its spectrum (a plot of intensity as a function of wavelength)- Use Stefan-Boltzman law; A hotter black-body is more luminous- Use Wien’s Law; A hoter blackbody peaks at a shorter wavelength (higher energy)2. Absorption Lines- Each atom has a unique spectrum- An electron absorbs the energy of a photon to go to a higher energy level- The atoms absorb light leaving a star- The absorption lines present depend on the temperature- Stars classified from O (hottest stars) BAFGK to M (cooler stars)- Balmer Thermometer – Lines of each atom or molecule are strongest at a particular temperature. 10.) Exciting an atom- Electrons have energy levels- It takes more energy to raise the electron to a higher energy level- In order to go from one energy level to another, it must emit or absorb exactly the right amount of energy- Absorption of light can excite atoms since light photons contain energy (E=hf)- Two ways to excite an atom: 1.) Absorption of a photon. 2.) Collisions of free electrons. 11.) Determining the size of a star- Using the equation for luminosity (L=4piR2sigmaT4) - Radius has a direct relationship with Luminosity- So a bigger star is more luminous- The main-sequence- Stars have a temperature appropriate for their luminosity - 90% of stars, including our sine, exist on the main-sequence- Stars spend 90% of their lives on the main-sequence- Mass of a star pretty much determines how hot and luminous a star is- Stars range from 0.08 solar masses to greater than 200 solar masses. 12.) Hertzsprung-Russel Diagram- A plot of luminosity as a function of temperature (luminosity on Y-axis) (temperature on X-axis)- Stars near the left of the diagram have a higher temperature- Stars near the top of the diagram are more luminous13.) Hydrostatic Equilibrium –The balance between weight (gravity) and pressure- Larger gravity means larger pressure- Outward pressure = inward force of gravity- Density, temperature, and pressure increase toward the center. Pressure and TemperatureHow can a star support itself?- The star must provide very high pressure in its center to support the overlying layers- Relationship between pressure and temperature: 1. Ideal Gas Law: P = nkT (Pressure = density x constant x Temperature)- If a star could attain a high temperature at its center, it would be more likely to be able to provide the pressure required to support its immense weight- Density, temperature, and pressure increase toward the centerFusion- Stars do nuclear fusion in their core- Nuclear fusion will release energy that will heat the gas, producing the large pressure needed to support the star- Fusion – Combining