Why is the Sky dark at Night?/quiz

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1 Approximately how often does a supernovae occur in a typical galaxy?

once a 5 months
once every 5 years
once every 50 years

2 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

3 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

4 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?


5 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

6 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

7 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

8 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