The__________is a theory that proposed to account for spiral arms ...

[biggirl4568]

The__________is a theory that proposed to account for spiral arms as compressions of the interstellar medium in the disk of the galaxy.
 
  A) spiral relativity theory
  B) spiral density wave theory
  C) spiral tracer theory
  D) spiral arm theory

Question 2

In 1912, after studying a star cloud called the Small Magellanic Cloud, Henrietta Leavitt concluded that:
 
  A) stars are eternal and unchanging.
  B) the brightest stars have the shortest pulsation periods.
  C) the Sun and Earth are near the edge of our Galaxy.
  D) there was a relationship between pulsation periods and luminosities of stars.

[sylvia]

Answer to Question 1

B

Answer to Question 2

D

[biggirl4568]

Great answer, keep it coming

[duy1981999]

Thanks for the timely response, appreciate it