Frontiers and Controversies in Astrophysics Notes

  • Frontiers and Controversies in Astrophysics Lecture 1

    About this course:\n\nThis is not a survey course. Three topics that will be covered in detail are extrasolar planets, black holes, and dark energy. What these things have in common is that they were all discovered or confirmed to exist recently and are now major topics of science. These objects cannot be observed directly but were instead detected by their effects, especially gravitational effects, on objects around them. The math for this course is ninth grade level, but it is hard because of how it is applied."},{"left":"What are the three planetary orbit theories?\n\nWhat is the moral of the Epicycle Fabel?","right":"Planetary Orbits


  • Frontiers and Controversies in Astrophysics Lecture 2

    MKS units stands for meters, kilograms, and seconds. Use scientific notation. In the form of N\\*10^m must be an integer in this class, If m is odd, to take the square root group it into (N\\*10)^(1/2)\\*10^((m-1)/2). In this class 3\\*10^7 seconds in an hour. G=7\\*10^-11. Use approximations, for example 7/4=2 and 3=pi=sqrt(10). NO CALCULATORS. NO ANDROIDS (decimals, use only one digit and scientific notation)."},{"left":"What are the best units for D1, D2, and a and why are these the best units?\n\


  • Frontiers and Controversies in Astrophysics Lecture 3

    Exoplanets can be detected by the motion they force their stars to make according to Newton's third law, the conservation of momentum. Momentum is defined as m\\*v (Mass times velocity), and it must be constant in a system at all times. The equation for conservation of mass in a planet-star system is VpMp=-VsMs. Both the planet and the star orbit around the center of mass/gravity which is found with the equation DpMp=DsMs. Other useful equations include Vp+Vs=Vtot, and Dp+Ds=Dtot, which in nearly circular orbits becomes Dp+Ds=maxDtot=a. Useful facts include 1SM=2\\*10^30kg, mEarth=6\\*10^24kg, mjupiter=2\\*10^22kg, and Vs<<Vp due to the great difference in mass."},{"left":"What is the scientific method of Observational Sciences?\n\n ","right":"Because Astronomy is an observational science, the traditional scientific method taught in schools does not work. Instead, Astronomers follow the scientific method for observational


  • Frontiers and Controversies in Astrophysics Lecture 4

    To observe exoplanets using the law of Conservation of momentum the following equations are useful: VpMp=-VsMs, DpMp=DsMs, maxDtot=a from the equations a^3=P^2M (for nearly circular orbits), in circular orbits: V=(2pia/p). \n\n \n\nExample: Find the velocity of the Earth\n\nThe Earth's orbit is nearly circular, so v=(2pia)/p=(2pi1AU)/1y=(2\\*pi\\*1.5\\*10^11)/(3\\*10^7)=(2\\*1.5\\*10^11)/(10^7)=(3\\*10^11)/(10^7)=3\\*10^4 m/s=30 km/s. \n\n \n\nExample: How fast does the sun move in response to the motion of Jupiter?\n\nThis is a question from the Law of Conservation and needs the equation VpMp=VsMs. We want Vs, so we solve for Vs getting the equation Vs=(VpMp)/Ms=(1.5\\*10^4\\*2\\*10^27)/(2\\*10^3)=15 m/sec. This size of movement is detectable in other stars. \n\n \n\nExample: How fast does the sun move in response to the motion of the Earth?\n\nAgain the equation VsMs=VpMp is used and rearranged to Vs=(VpMp)/Ms=(3\\*10^4\\*6\\*10^24)/(2\\*10^30)=(3\\*10^4\\*3\\*10^24)/(10^30)=(10^29)/(10^30)=10^-1=10 cm/sec. Not detectable in other stars."},{"left":"What is the Doppler Shift?\n\nHow fast do you have to go to mak


  • Frontiers and Controversies in Astrophysics 5

    Important from Problem Sets\n\nThe center of mass does not move, or it moves at a constant velocity. The center of mass does not accelerate. All objects in a solar system orbit around the center of mass. Furthermore, the orbital period is the same for both the planet and the star. Each planet's gravity affects the orbits of the other planets. These wiggles are observable and have been used to discover planets. Radial velocity is not the same as regular velocity, it does not catch sideways motion, only edge on motion."},{"left":"What is used to show that the motion of a star is due to the orbital of a planet?\n\nHow are multiple planet sys


  • Frontiers and Controversies in Astrophysics Lecture 6

    Smaller planets with highly elliptical orbits do not cause sine curve like graphs of radial velocity in their stars.  Evidence from the velocity of stars shows that hot Jupiters exist, but the method of their formation is unknown."},{"left":"What gave solid evidence for the existance of HD209458's Hot J


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