ASTRONOMY FINAL CUMULATIVE EXAM REVIEW Astronomy The science that deals with the material universe beyond the Earth s atmosphere This is NOT astrology Scientific observation hypothesis You never simply get to be right Qualitative Quantitative Units Meter The distance traveled by light in 1 299 729 458 of a second Second A duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium 133 atom Kilogram The mass of a chunk of some stuff in France One Light Year The Earth is 8 light minutes from the Sun Speed of light is 3x10 m s Geocentric Universe The Earth s axis is actually tilted with respect to the plane of its orbit Claudius Ptolemaeus Ptolemy constructed the best geocentric model Earth is the center of the universe Each planet orbits Earth and at the same time moves in circles about that orbit epicycle Problem Full model required at least 80 separate circles Heliocentric View Copernican Revolution Used circular orbits for planets about the Sun Proved wrong Both models geocentric and heliocentric have phases for Venus However they re both distinctly different Venus Phases Empirical Laws The what as opposed to the why Empirical theories are strictly observational there s no deeper meaning to the equations beyond what they state Theories that start from first principles are far deeper I start with the assertion that the universe Kepler s 1st Law diameter Kepler s 2nd Law Kepler s 3rd Law acts in a certain way and then everything else is a consequence The circle is not a perfect form Orbits are ellipses with the Sun at one focus Any given point on the ellipse has the same sum of the distances from each focus the major Perihelion The point of closest approach to the Sun Aphelion The greatest distance from the Sun Semi Major Axis a Half the length of the long side of the ellipse Eccentricity The distance between the foci divided by the length of the major axis The larger the eccentricity is the more elongated the ellipse is A circle is just an ellipse with eccentricity zero While orbiting the Sun an imaginary line connecting Sun and planet sweeps out equal areas of the ellipse in equal intervals of time Gravity central force This law has everything to do with the way gravity is acting P 2 a 3 The square of a planet s orbital period is proportional to the cube of its semimajor axis how far away you are from the sun Orbital period Time taken to traverse the full elliptical orbit Newton s 1st Law of Motion You have to have something acting in order to change the state of an object s motion An object at rest remains at rest and a moving object continues to move forever in a straight line with constant speed unless some external force changes their state of motion Newton s 2nd Law of Motion F ma The acceleration of an object is directly proportional to the net applied force and inversely proportional to the object s mass Acceleration is the rate of change of velocity or speed Inversely proportional to mass The heavier you are the less you accelerate for the same force applied If you re not accelerating the net force is zero Newton s 3rd Law To every action there is an equal and opposite reaction I exert a force on something it exerts the same force in the opposite direction on me The force of gravity of the earth on the sun is the exact same as the force of gravity of the sun on the earth THEY RE EQUAL Accelerating things has to do with the net force being put on an object Newton s law of Universal Gravitation Every particle of matter in the universe attracts every other particle with a force that is directly proportional to the product of the masses of the particles and inversely proportional to the square of the distance between them G Newton s constant 6 67x10 11 Nm kg F GM M r M a If I drop you and an anvil you accelerate at the same rate even though you have different masses F m a redux Since the anvil is more massive the force of gravity is proportionally stronger on it providing the same acceleration Weight and Mass gravity on a given mass fundamental constant factor Weight can be different in different places depending on where you are Weight is the force of Mass is always the same no matter where you are the amount of stuff in you Mass is a In practice people interchange them because the difference here on Earth is one mostly Remember that gravity is constantly working Modified Kepler Law The Sun and the Earth feel equal and opposite gravitational forces Newton s 3rd law This has to modify Kepler s laws in the following way The orbit of a planet about the Sun is an ellipse having the center of mass of the planet Sun system at one focus The orbital period is related to the semi major axis of the orbit by P 2 a 3 M M is now the combined mass in units of the Sun s mass Matter Atoms are made up of protons neutrons and electrons Protons and Electrons have electric charge Matter made up entirely of a single type of atom is known as an element Electric and Magnetic Fields Any charged particle creates an electric field This field creates a force on other charged particles in the area Like repels like Opposites attract field and vice versa Moving charged particles create a magnetic field with a corresponding magnetic force Electric and Magnetic fields are inextricably linked A changing electric field causes a magnetic Light as a wave Remember light can be both a wave and a particle Though light appears continuous it actually is discrete little packets or quanta And each quanta of light has an energy E hf where h is Planck s constant and f is the frequency Electromagnetic waves A varying electric field causes a varying magnetic field which in turn causes a varying electric field and so on The result is a self sustaining electromagnetic wave The process can become self sustaining Everything that has mass cannot go the speed of light Doesn t require a medium it isn t a distortion like a water wave but the changes in the electric and magnetic fields Waves Amplitude Frequency Wavelength Telescopes blurring you are Detectors Resolution Resolution is important Capture as much as possible the radiation light and concentrate it for study Two basic kinds of telescopes Refracting Use lenses to bend beams of light Galileo Reflecting Use curved mirrors to collect and concentrate light Newton Chromatic aberration light bends more or less depending on wavelength Most modern observatories use reflecting telescopes