Name_________________________

STUDENT INSTRUCTION AND ANSWER SHEET

Activity 2: How Bright is too Bright for Life?

The brighter a star is, the more radiation it gives off, and most of the radiation tends to be at higher frequencies. The Sun emits most of its radiation in the visible frequency range. In general, the higher the frequency of the emitted radiation, the more damaging it is to complex life. For Earth-like life forms, ultraviolet radiation is highly damaging to cells and to DNA. In Graph 2, stellar radiation frequency is plotted on the vertical axis, and stellar luminosity is plotted on the horizontal axis. Use this information and Graph 2 to answer the following questions.

log-log graph of stellar radiation frequency versus stellar luminosity

A. Find the location of visible radiation on the stellar radiation frequency axis of Graph 2. Find the stellar luminosity that corresponds with this frequency. How does this value compare to the luminosity of the Sun?

 

B. Place a mark on the stellar luminosity axis that represents your estimate for the limit on how bright a star can be before the frequency of most of its radiation is too damaging for Earth-like complex life to develop easily. Label this mark as either Lmin2 or Lmax2. How did you decide which should it be?

 

 

C. In Activity Page One, you made an estimate for Lmax1 and marked it on Graph 1. In the previous question (B), you made an estimate for Lmax2 and marked it on Graph 2. Do your estimated values of Lmax1 and Lmax2 both predict the same result for the existence of complex life? Explain your reasoning.

 

 

 

D. Explain why Lmax1 is a limit on how bright a star can be and still have complex life on a nearby planet.

 

 

E. Explain why Lmax2 is a limit on how bright a star can be and still have complex life on a nearby planet.

 

 

F. Predict whether or not complex life could exist on a planet near a star that: (1) has a main sequence lifetime equal to the time it took for complex life to develop on Earth, and (2) gives off radiation that is mostly in the UV range. Explain your reasoning.

 

 

G. Predict whether or not complex life could exist on a planet near a star that: (1) has a main sequence lifetime much shorter than the time it took for complex life to develop on Earth, and (2) gives off radiation that is mostly in the visible range. Explain your reasoning.

 

 

H. Imagine that Lmax1 is greater than Lmax2 for a star, which value sets the limit for how bright a star can be and still have complex life on a nearby planet? Explain your reasoning.