All the following statements are true. Which one explains why our calendar has leap years?
A) Earth's axis precesses with a period of about 26,000 years.
B) There is a difference between a sidereal year and a tropical year.
C) A tropical year is slightly more than 365 days.
D) Earth's speed varies as it orbits the Sun.
C
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Most of the energy emitted by a pulsar _____
a. is carried away as a ‘pulsar wind' of high-speed atomic particles b. produces strong gravitational waves that radiate for several light years c. ionizes the supernova remnant around the pulsar d. is in the form of neutrinos e. is carried away by the high-energy beam emerging from the poles of the pulsar
What is the Celestial Equator?
A. a band of constellations through which the planets and Sun appear to move B. the cycle of lunar phases C. the line that the Sun traces across the celestial sphere D. an imaginary line in the sky, directly above Earth's equator
The maximum theoretical efficiency of a Carnot heat engine operating between reservoirs at the steam point and at room temperature is about:
A. 10% B. 20% C. 50% D. 80% E. 99%
The fundamental nuclear reaction occurring in the core of the Sun is ________
A) nuclear fusion of helium into carbon B) nuclear fusion of hydrogen into helium C) radioactive decay D) nuclear fission