The Motion of the Universe

What Keeps Celestial Bodies in Orbit?  The First Person to attempt to answer this question was Isaac Newton  Formulated the Law of Universal Gravitation Every object in the universe attracts every other object Force of gravity depends on two factors  Mass of the object If mass increases, gravity increases  Distance between objects If distance increases, gravity decreases

So why doesn’t Earth fall into the Sun?  Remember Newton’s First Law of Motion: Inertia keeps it in motion!  Law of Inertia States: An object at rest will stay at rest or an object in motion will stay in motion unless acted on by a force This holds true for all objects orbiting other objects in the universe!

Kepler’s First Law: Orbits of Celestial bodies  Kepler's first law - sometimes referred to as the law of ellipses - explains that planets are orbiting the Sun in a path described as an ellipse

Kepler’s Second Law  The speed at which any planet moves through space is constantly changing.  A planet moves fastest when it is closest to the Sun and slowest when it is furthest from the Sun.  But if a line were drawn from the center of the planet to the center of the sun, that line would create a triangle of equal area.  dia/circmot/ksl.html dia/circmot/ksl.html

Newton vs. Einstein  Newton thought that gravity was an instant force and did not take time to travel. (gravity is a pull)  Einstein felt gravity moved like light – at a particular speed and propagated out from a source

Einstein’s Theory of General Relativity  Objects warp space  Objects orbit because they are pushed into indentations that are created by other larger objects not because of a force that is pulling on an object.

Big Bang Theory – Best Guess!!  All celestial bodies in universe are made of the same 92 elements  Spectral analysis using black line spectrum Found celestial bodies in universe are moving apart - black lines shifted to red side of spectrum  Hubble telescope discovered background radiation leftover from Big Bang

 Red shift Red shift The shift in the visible light spectrum of a light to the red The shift in the visible light spectrum of a light to the red end of the spectrum Object is moving away from observer Object is moving away from observer  Blue shift Blue shift The shift in the visible light spectrum of a light to the blue/violet end of the spectrum The shift in the visible light spectrum of a light to the blue/violet end of the spectrum Object is moving toward observer Doppler effect applied to stellar movement Longer wavelengths = red color Shorter wavelengths = Blue wavelengths

Doppler shift applied to stellar movement

Spectral Analysis  Study of a star’s spectrum to determine composition, motion in space, and general temperature, pressure and rotational speed. (we will talk about this later) Astronomers produce spectra by means of a "spectrograph" affixed to the telescope.