Last class: reflection, refraction, simple optics and use in telescopes. Now: how we can use the properties of electromagnetic radiation to derive information about the stars

But what can we learn about them? They’re DARK NB can see with ground based & model

Resonant interaction with Galatea (Tremaine, Baudry & Goldreich confines azimuthally. Holland et al -> mass of dust a few lunar masses so planets already formed. Neptune at 30 AU. 90 AU ~ 90x 90 = 8 Billion miles

First ask where do stars form? how do we detect these structures?

Gravitational effects of planet means star orbits center of mass of system. Over 30 yrs, Sun moves thus, mostly (70%) due to Jupiter. Mjup ~ 1/1000Msun, so c.of m. 1000x closer to Sun than Jup. Total wobble 4mas =separation of headlights of car at 20,000km. Easiest to detect velocity variations, especially for planets close to star which move fast 12m/sec due to Jup. Astrometry a difficult measure