Why is the Sky dark at Night?/quiz

{Approximately how often does a supernovae occur in a typical galaxy?} - once a 5 months - once every 5 years + once every 50 years {If a star were rushing towards Earth at a high speed} + there would be a blue shift in the spectral lines - there would be a red shift in the spectral lines - there would be no shift in the spectral lines {An example of a standard candle is} - any part of the nighttime sky that is giving off light - any part of the nighttime sky that is dark + a supernova in a distant galaxy - all of these are standard candles {If a galaxy that is 10 Mpc away is receding at 700km/s, how far would a galaxy be receding if it were 20 Mpc away?} - 350km/s - 700km/s + 1400km/s {The "apparent" magnitude of a star is} - How bright it would be if you were exactly one light year away - How bright it would be if it were not receding due to Hubble expansion + How bright it is as viewed from Earth {In the essay "Why the sky is dark at night", a graph of velocity versus distance is shown. What is odd about those galaxies in the Virgo cluster (circled in the graph)?} - they all have nearly the same speed + they have a wide variety of speeds - they are not receding away from us - the cluster is close to us {Why was it important to observe supernovae in galaxies that are close to us?} + we have other ways of knowing the distances to the nearby galaxies; this gives us the opportunity to study supernovae of known distance and ascertain their absolute magnitude. - they have less of a red-shift, and interstellar gas absorbs red light - it is easier to measure the doppler shift, and that is not always easy to measure. - because supernovea are impossible to see in distant galaxies {What if clouds of dust blocked the light from distant stars? Could that allow for an infinite and static universe?} + No, the clouds would get hot - No, if there were clouds, we wouldn't see the distant galaxies - No, there are clouds, but they remain too cold to resolve the paradox - Yes, that is an actively pursued hypothesis