Suppose you gathered a ball of interstellar gas that was equal to the size of the Earth (a radius of about 6400 km). If this gas has a density of 2.8 hydrogen atoms per cm3, typical of the interstellar medium, what would its total mass be? (For comparison, a bowling ball has a mass of about 5 kg) (HINT: 2.8 hydrogen atoms per cm3 corresponds to a density of 4.68 × 10−21 kg/m3)

In a globular cluster, astronomers (someday) discover a star with the same mass as our Sun, but consisting entirely of hydrogen and helium. Is this star a good place to point our SETI antennas and search for radio signals from an advanced civilization? Group of answer choices   No, because such a star (and any planets around it) would not have the heavier elements (carbon, nitrogen, oxygen, etc.) that we believe are necessary to start life as we know it.   Yes, because globular clusters are among the closest star clusters to us, so that they would be easy to search for radio signals.   Yes, because we have already found radio signals from another civilization living near a star in a globular cluster.   No, because such a star would most likely not have a stable (main-sequence) stage that is long enough for a technological civilization to develop.   Yes, because such a star is probably old and a technological civilization will have had a long time to evolve and develop there.

How many Big Macs can fit in the Grand Canyon taking into account gravity and the varying dimensions of the Grand Canyon?

What evidence can you cite that the interstellar medium contains both gas and dust? (Select all that apply.) (1)The dust of the interstellar medium can be detected from the emission lines of elements heavier than iron. (2)The dust of the interstellar medium can be detected by the extinction of light from distant stars. (3)The dust of the interstellar medium can be detected by the scattering of blue light from distant or embedded objects. (4)The gas of the interstellar medium can be detected from the radiation of ultraviolet photons. (5)The gas of the interstellar medium can be detected from the radiation of photons of wavelength 21 cm. (6)The gas of the interstellar medium can be detected from the absorption lines present in the light from distant stars, which must be caused by a medium of a density and temperature other than that of the stars emitting the light.