If we say that a galaxy has a lookback time of 1 billion years, we mean that
A) its light traveled through space for 1 billion years to reach us.
B) it is now 1 billion light-years away.
C) it was 1 billion light-years away when the light left the galaxy.
D) it is 400 million years old.
A) its light traveled through space for 1 billion years to reach us.
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Looking for an Earth-size planet around a nearby star (besides the Sun) is like looking for a pinhead located ________
A) across the street B) a few hundred kilometers away C) thousands of kilometers away D) across the length of a football field
The heat of vaporization of ethyl alcohol Lv is about 200 cal/g. That means that 1 gram of this refrigerant upon vaporization would release
A) less then 200 calories. B) 200 calories. C) more than 200 calories.
Over geologic history the Earth's magnetic field
A) has been relatively stable. B) has increased in strength exponentially. C) has reversed direction many times. D) is unknown.
Alice is floating freely in her spacecraft, and you are accelerating away from her with an acceleration of 1g. How will you feel in your spacecraft?
A) You will be floating weightlessly. B) You will feel weight, but less than on Earth. C) You will feel weight, but more than on Earth. D) You will feel the same weight as you do on Earth. E) You will feel yourself pressed against the back of your spaceship with great force, making it difficult to move.