Define.
A system of stars orbiting a common center of gravity.
A. Solar system
B. Universe
C. Galaxy
D. Biosphere
C. Galaxy
The correct answer for the definition of a system of stars orbiting a common center of gravity is C. Galaxy.
To arrive at the correct answer, let's break down the options and eliminate the incorrect ones:
A. Solar system: A solar system refers to a star, in this case, our Sun, and all the celestial bodies like planets, moons, asteroids, comets, etc., that orbit around it. Since this definition does not fit the given criteria, we can rule out option A.
B. Universe: The universe encompasses everything that exists, including all matter, energy, time, and space. While a system of stars can be found within the universe, the word "universe" itself does not specifically define a group of stars orbiting a common center of gravity. Thus, option B is not the correct answer.
C. Galaxy: A galaxy is a massive collection of stars, stellar remnants, interstellar gas, dust, and dark matter held together by gravitational forces. Galaxies consist of billions to trillions of stars that orbit a common center of gravity known as the galactic core. Each galaxy can have its own structure, such as elliptical, spiral, or irregular. This matches the given definition, so option C is the correct answer.
D. Biosphere: The biosphere refers to the regions of the Earth, including the atmosphere, lithosphere, and hydrosphere, where life exists. This concept is not directly related to a system of stars orbiting a common center of gravity, so option D can also be eliminated.
In summary, the correct answer for the given definition is C. Galaxy