11. A few years after the debate, a famous astronomer calculated the distance of

Question

11. A few years after the debate, a famous astronomer calculated the distance of one of these spiral nebulae, proving that spiral nebulae are indeed giant galaxies (“island universes”) similar to our own Milky Way but far outside the Milky Way? Who did this? A) Lord rose B) Edwin Hubble C) Harlow Shapley D) Immanual kant E) Heber Curtis

12. What is being “flipped” when a hydrogen atom emits a photon of 21-cm radiation? A. The spin of the electron. B. A neutron. C. Nothing is flipped. D. The whole hydrogen atom.

13. Using radio telescopes to observe 21-cm radiation, astronomers were able to produce a map of what place? A. Sunspots B. Our solar system C. Our Milky Way galaxy D. The Universe

14.For a neutron star (including pulsars), does the magnetic axis coincide with the axis of rotation? In other words, do they make the same line? A. Yes, they line up B. They are not lined up the same

15. For the next few questions, consider the diagrams in Figure 12-21 of your textbook and the comments within it: According to the diagram, what happens to electrons and other particles that are pulled on by a neutron star’s magnetic field? A. They produce radiation (light) that forms a beam from each pole of the neutron star. B. They are pulled onto the neutron star’s surface and make the neutron star heavier. C. They are unaffected by the magnetic field. D. They cause the magnetic field to lose strength gradually.

Explanation / Answer

11. B :- Edwin Hubble measured the distance of the M31, the Andromeda Nebula using several Cepheid variable stars ( Cepheid stars, they have a very specific relationship between their variability period and their luminosity so we can find the distance.). Hubble showed that distance of the M31 is far greater than that of the size of Milky way so they exists outside the Milky Way.

12. A :- The spin of the electron flips and therfore atom emits a 21 cm long wavelenght radio wave.

13. C :- Using that 21 cm long wavelenght radio wave astronomers mapped our Milky Way Galaxy as every stars of this galaxy have hydrogen as a primary component.

14. B :- Pulsars do not have their rotation axis aligned with the magnetic axis. Due to this property they seem to pulsate the elecromagnetic waves. Remember they emit EM waves continuously, it is the non - alignment that causes them to pulsate.

15. A :- Faster rotation of pulsars causes the magnetic field to rotate faster so this rotating magnetic field produces an elecrical field and therefore resulting in the acceleration of protons and electrons on the pulsar star surface and the creation of an electromagnetic beam emanating from the poles of the magnetic field.

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