The identification of "spiral nebulae" as large groupings of stars outside of our own galaxy was proven by ____
a. photographic plates made by Edwin Hubble showing stars and Cepheid variables
b. the results of the Shapley-Curtis debate
c. Immanual Kant's "island universe" theory
d. William Parsons' observation and description of their spiral structure
e. Harlow Shapley's observations of their radio spectrum
a
You might also like to view...
A wooden raft has a mass of 50 kg. When empty it floats in water (density 1000 kg/m3 ) with 69% of its volume submerged. What mass of sand can be put on the raft without it sinking?
What will be an ideal response?
What condition or conditions is/are necessary for rotational equilibrium?
A) ?Fy = 0 B) ?Fx = 0, ?Fy = 0 C) ?? = 0 D) ?Fx = 0 E) ?Fx = 0, ?Fy = 0, ?? = 0
What happens to the atomic number (Z) and the mass number (A) when a nucleus emits an alpha particle?
a. Z increases by 1; A is unchanged. b. Z is unchanged; A is unchanged. c. Z decreases by 2; A decreases by 4. d. Z decreases by 1; A is unchanged.
Two isotopes have the same mass number
a. True b. False Indicate whether the statement is true or false