In the measurement of distances _beyond_ the solar system the unit employed is either the _light-year_ or more recently the _parsec_, which is rapidly replacing the light-year among astronomers. A "light-year" is the distance that light, with its finite but almost unimaginable velocity of one hundred and eighty-six thousand miles _per second, travels in a year_. It is equal in round numbers to sixty-three thousand times the distance from the earth to the sun or approximately six thousand billions of miles. The parsec is equal to three and twenty-six hundredths (3.26) light-years, and it is approximately two hundred thousand times the distance from the earth to the sun. It is "the distance of a star with the _parallax_ of a second," a fact which its name, parsec, conveys to us. In other words, at the distance of one parsec the distance from the earth to the sun, "the astronomical unit," would subtend an angle equal to one second of an arc. This angle is spoken of as the parallax of the star. The larger the parallax, that is, the larger the angle the astronomical unit or radius of the earth's orbit subtends, viewed from the star, the nearer the star is to us. The fact that there is no known star within one parsec, or three and twenty-six hundredths light-years, of the sun shows the immensity of the scale of the universe of stars.