Why is Earth's orbit often referred to be a "nearly perfect circle" and not a true ellipse?
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Earth's orbit is only very slightly elliptical. Around January 3, Earth is at perihelion, its closest point to the Sun, when it is only 1.7 percent closer than average. Around July 5, Earth is at aphelion, its most distant point from the Sun, when it is only 1.7 percent farther than average.
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Astronomers can measure a star's mass in only certain cases. Which one of the following cases might allow astronomers to measure a star's mass?
A) The star is a member of a binary star system. B) The star is of spectral type G. C) The star is of spectral type A. D) We know the star's luminosity and distance.
Which of the following best sums up current scientific thinking about the nature of dark energy?
A) Dark energy most likely consists of a form of photons that we can't see or detect. B) Dark energy is most likely made up of weakly interacting particles that do not interact with light. C) Dark energy probably exists, but we have little (if any) idea what it is. D) Dark energy is the source of the mind weapon used by Sith Lords in Star Wars.
State the Third Law of Thermodynamics
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A particle of interplanetary dust is close to the Sun and interacts with the Sun's gravitational field as well as with the light emitted by the Sun
If it only interacts appreciably with the Sun, can it be pushed away from the Sun instead of being pulled towards it? A) No, the gravitational force will always dominate if the object is large enough. B) No, the gravitational force will always dominate if the object is close enough. C) Yes, if the object is small enough, radiation pressure will win over. D) Yes, but the object must be very large so that it can gain enough radiation pressure. E) None of the previous answers is correct.