All the following statements are true. Which one explains why our calendar has leap years?
A) A tropical year is slightly more than 365 days.
B) Earth's axis precesses with a period of about 26,000 years.
C) There is a difference between a sidereal year and a tropical year.
D) Earth's speed varies as it orbits the Sun.
A) A tropical year is slightly more than 365 days.
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Plasmas are a central part of power generation in
A) MHD generators. B) turbo generators. C) both of these D) neither of these
A thin layer of oil (n = 1.25 ) is on top of a puddle of water (n = 1.33 ). If normally incident 500-nm light is strongly reflected, what is the minimum nonzero thickness of the oil layer?
A) 250 nm B) 100 nm C) 400 nm D) 200 nm E) 150 nm
What causes some asteroids leave the asteroid belt and sometimes approach Earth?
A. Because Earth's gravitational field attracts them. B. Because Jupiter's gravitational field ejects them. C. Because they crash into one another and get ejected.
There are three types of collapsed, burned-out stars: black holes, white dwarfs, and
A) X-ray stars. B) supernova. C) neutron stars. D) quasars. E) red giants.