Why wasn't the intracluster medium in galaxy clusters discovered until the 1960s?
A) We did not know how much dark matter existed before then.
B) We didn't have the resolution to observe galaxy clusters until then.
C) The Milky Way was blocking our view of distant galaxy clusters.
D) The medium emits X-rays, which are blocked by the Earth's atmosphere and require X-ray satellites in space in order to be observed.
E) Radiation emitted by the medium was so dim that we couldn't detect it until we built much larger telescopes.
D
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The tidal stresses that create Io's volcanism come from Jupiter and
A) Titan. B) the Sun. C) Callisto. D) Europa. E) Ganymede.
Which of the following statements about apparent and absolute magnitudes is true?
A) A star's absolute magnitude is the apparent magnitude it would have if it were at a distance of 10 parsecs from Earth. B) The magnitude system that we use now is based on a system used by the ancient Greeks over 2,000 years ago that classified stars by how bright they appeared. C) A star with an apparent magnitude of 1 appears brighter than a star with an apparent magnitude of 2. D) The absolute magnitude of a star is another measure of its luminosity. E) All of the above are true.
If you keep decreasing the kinetic energy of atoms in a liquid, the liquid may
A) melt. B) condense. C) solidify.
Consider the following circuits. The batteries and capacitors are identical, and the switches have been closed for a very long time