Ch8 Interstellar Travel Why you can’t get there from here (easily).

Ch8 Goals What is the average distance between stars? How long will interstellar travel take? What is Time Dilation? What will we find when we get there?

Ch8 Average Distances Depends on where. –Spiral arms – 2 pc (7 LY) –Bulge – 0.3 pc (1 LY) –Globular cluster – 0.03 pc (1 Light Month!) M10 – copyright Credner and Kohle

Ch8 How Fast? Voyager 1 (launched 1977) –Fastest machine made by humanity. –Velocity = 62,000 km/hr (37,000 mph) Current location: –87.5 AU (Pluto = 40 AU) –12 Light Hours Compare model solar system in class to Voyager’s “model speed.” 0.04 miles per year = 0.3 inches per hour!

Ch8 How Long? Time = (distance between stars)/velocity For Voyager 1 in: –Spiral arms = 110,000 years –Bulge = 17,000 years –Globular cluster = 1700 years M10 – copyright Credner and Kohle

Ch8 Special Relativity Einstein (1905): –Speed of light is a constant. –Impossible to distinguish moving and non-moving frames of reference. Results: –Moving clocks run slow. –Moving meter sticks get short. Our ticket to the stars!

Ch8 Special Relativity 2 Main Postulates: 1. The speed of light is always c. Thou shalt not add your speed to the speed of light!

Ch8 Special Relativity 2. Moving and non- accelerating reference frames are indistinguishable from one another. If it happens at rest, it must happen in (constant) motion. Are you moving, or are you at rest right now? At restConstant velocity

Ch8 Time Dilation Tick! Tock! Tick! Tock! Compare

Ch8 Moving clocks run slow Since: Compare S

Ch8 How slow? Travel to Vega: Distance = 25 LY (7.5 pc) Time = Distance / velocity velocity = 0.999c Time Rest = 25 years Time Moving = 25 years x 0.04 = 1year! Copyright Lynette Cook, used with permission

Ch8 How slow? Travel to Milky Way’s supermassive black hole: Distance = 28,000 LY (8.5 kpc) Time = Distance / velocity velocity = c Time Rest = 28 thousand years Time Moving = 28 thousand years x = 40 years!

Ch8 What will we find there? Copyright Lynette Cook, used with permission Are there planets around other stars?

Ch8 Reflex Motion The Moon doesn’t orbit the Earth. The Earth doesn’t orbit the Sun. What do they do? They each orbit their combined center of mass. X

Ch8 Reflex Motion A star with planets wobbles.

Ch8 Doppler Shifts Light goes at velocity = c (always!) For moving object: –In front: light waves bunch up –Behind: light waves spread out Color is simply wavelength of light –Blue = short wavelengths –Red = long wavelengths Moving objects appear different colors.

Ch8 Doppler Shifts Movement towards or away yields Doppler shifts. You X

Ch8 Doppler Velocity From Doppler shifts we get a velocity and period.

Ch8 Johannes Kepler Kepler’s Second Law: Kepler’s Third Law: With tweaking by Newton:

Ch8 Result: 51 Pegasi Mayor and Queloz a = AU Copyright Lynette Cook, used with permission

Ch8

Ch8 Upsilon Andromedae Copyright Lynette Cook, used with permission

Ch8 But Are They Real? Copyright Lynette Cook, used with permission

Ch8 Planet Shadows

Ch8 HD Based on Doppler curve, knew when planet might pass in front of its star. Published times to look. Greg Henry (Tennessee State Univ.)

Ch8 Copyright Lynette Cook, used with permission

Ch8 Savage et al Hubble Space Telescope

Ch8 Marcy and Butler

Ch8 Worlds without End? Known Planets: –In our Solar System: 9 –Outside our Solar System: 110 Known Multi-Planetary Systems: –Prior Sept. 1995: 1 (ours) –As of Oct. 2004: 10 Copyright Lynette Cook, used with permission