Contrast the sizes and membership of the Local Group and Virgo Cluster
What will be an ideal response?
Our Local Group is only 55 members, and about 1 Mpc across. The Virgo Cluster lies about 18.5 Mpc distant, is roughly 3 Mpc across, and contains more than 2500 galaxies.
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For a plane to be able to fly clockwise in a horizontal circle as seen from above, in addition to exerting a force downwards on the air
a. it must be increasing its speed. b. it must exert a force on the air that is directed to the plane's left side. c. it must exert a force on the air that is directed to the plane's right side. d. it does not need to exert a force: it must only move the wing flaps out. e. it only needs to deflect the air without exerting any additional force on the air.
Which of the following is not consistent with observations of the cosmic microwave background?
A) The universe is at least 20 billion years old. B) The universe is geometrically "flat" (in the four dimensions of spacetime). C) Dark energy, whatever it is, represents the majority of the energy content of the universe. D) The matter density (both luminous and dark matter combined) in the universe is only about one-fourth of the critical density.
Asteroid Ida was photographed by the Galileo spacecraft in 1993, and the photograph revealed that the asteroid has a small moon, which has been named Dactyl
From the dimensions of Ida and its general features, one can estimate the mass of Ida to be 4.5 × 1016 kg, and the distance between Dactyl and Ida is approximately 90 km. Assuming a circular orbit, what would be the orbital speed of Dactyl? (G = 6.67 × 10-11 N ? m2/kg2 ) A) 2.9 m/s B) 5.8 m/s C) 30 m/s D) 11 m/s E) 2.3 m/s
Theoretical calculations suggest that Earth-sized planets could be habitable on their surfaces outside of habitable zones if they
A) have thick, hydrogen atmospheres B) have thick carbon dioxide atmospheres C) are tidally heated by several large moons D) have larger irons cores