Hw 5 Solutions




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HW 5 Solutions


  1. What are “black smokers?” Where in our solar system would you find a similar environment where black smokers could thrive?

Black smokers are volcanic vents at the bottom of earth’s oceans. It was recently discovered that some of the oldest life forms on earth live in these harsh environments. This was a revolution in our understanding of life, since these organisms gain their energy not from the sun but from the interior of the earth itself—geothermal energy.

Black smokers, and with them possibly life, could exist on any moon or planet with a liquid ocean and hot, most likely tidally heated, core. Europa is a prime suspect, Ganymede, Callipso, Titan, and Enceladus are also possible candidates.


  1. How is 21 cm. radiation produced?

21 cm radiation refers to radio waves produced by neutral hydrogen atoms in cool regions of our galaxy and concentrated in the spiral arms. They are created because of hyperfine splitting in the energy levels of the electron in the ground state. The electron and proton in the hydrogen atom spin and the spins may be either aligned or opposite. Spins aligned is a slightly higher energy state. As the electron realigns itself into the lower energy state with spins opposite, the extra energy is given off as a low energy photon, with wavelength of 21 cm.




  1. Page 193 #20.

Figure 11.10: NGC 4414 is a spiral galaxy, with no bar, and numerous arms. Sc


Figure 11.11: NGC 1300 is a spiral galaxy, barred, and with two distinct arms. SBb
Figure 11.12: M87 is an elliptical galaxy that is almost entirely spherical. E0.


  1. How did Edwin Hubble use Cepheid variables to determine the distance to the Andromeda spiral nebula? Describe his method.

Cepheid variable stars are stars with changing luminosity. They grow brighter then dimmer in a repeating cycle that can be as short as a couple days or as long as an entire month. Astronomers have found that the period of this cycle and the star’s luminosity are directly related. This means that knowing the star’s period is the same as knowing its luminosity. While observing the Andromeda galaxy, Hubble took photographs over many days. By seeing how the Cepheid variable stars changed from day to day, he was able to measure their periods of variation. From the period/luminosity relation, he knew the star’s luminosity, the absolute magnitude. As we did in lab, the absolute magnitude in combination with the apparent magnitude gives us the distance modulus, which we can use to calculate distance.


  1. If the fastest airplane travels at 1600 km/h, how many years would it take for it to reach the star Sirius? The distance to Sirius is 8.3 light years. (Show work.)

1 LY = 9.46 x 10 12 km

So 8.3 LY = 8.3 LY x 9.46 x 10 12 km/LY = 7.85 x 10 13 km=distance traveled

Velocity = 1600 km/hr x 24 hr/day x 365 days/year =1.6 x 10 3 x 2.4 x 10 1 x 3.65 x 10 2 =

1.4 x 10 7 km/yr

So Time = Distance/ Velocity

= 7.85 x 10 13 km / 1.4 x 10 7 km/yr

= 5.6 x 10 6 years



= 5.6 million years!!!!



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