4. An asteroid is headed for Earth! Its closest approach will take it just above our...
4. An asteroid is headed for Earth! Its closest approach will take it just above our atmosphere, 500 km above sea level. As it passes the orbit of the Moon (385,000 km away), your instructor observes a hydrogen recombination emission line in the asteroid's thin atmosphere (at rest with respect to the asteroid). They measure a blueshift velocity of 30 km/s and tell you there's nothing to worry about. What spectral resolution (R - NAX) would your instructor's spectrograph need to have for you to believe them? Assume that Al is the uncertainty in spectral resolution (a very typical assumption for astronomers), and clearly state your minimum S/N assumed for a "believable" result. (4 pts)