The Hubble time is____
a. an estimate of the age of the Universe
b. the time needed for a galaxy to travel 1 Mpc
c. not connected to Hubble law of galactic redshifts
d. the time for light to cross the Universe
e. the time needed for galaxies to form
a
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The energy needed to change a He+ ion in the ground state into a He2+ ion is
a. 13.6 eV b. 54.4 eV c. 112.4 eV d. 92.9 eV e. 27.2 eV
In a Voigt solid with an elastic modulus of 1 GPa, if a tensile stress of 1 MPa is applied, the total strain after a long time is equal to _________.
Fill in the blank(s) with the appropriate word(s).
What evidence is there that supernovae really have occurred?
A) Crab Nebula B) supernova remnants C) existence of heavy radioactive elements in nature D) observations of the actual explosions E) All of the above.
When they were first discovered, quasars appeared to be____
a. small, star-like objects associated with radio emission b. pairs of radio sources c. elliptical galaxies with an X-ray emitting halo d. clouds of gas glowing with green emission lines e. linear jets of matter