Planetary transit
HD 209458 very similar to 51 Peg
- Star very similar to sun, about 45 l.y. distant
- Doppler shifts fit a circular orbit WWW vu-graph
- P = 3.5 days
- star’s velocity +/- 82 m/s
- minimum planet mass 0.6 Jupiter
- Transits would occur at the zero-crossing
- when planet is moving across our line of sight the Doppler shift is zero draw orbit on board
- Time of transit well known, look for dimming of starlight
- planet blocks a fraction of the stars surface
- The fraction is the area of the planet’s disk compared to the star’s
- Jupiters radius, 70,000 km, is 10% of the Sun’s
- Jupiter would block (0.1)2 = 0.01 = 1% of our Sun’s light