The mathematical principles of the Copernican model resulted in pushing the sphere of the stars many thousands of times further away from the sun than it had been in the earth-centered cosmos. When the sun-centered system gained acceptance in the seventeenth century, astronomers seized the telescope to directly test the numbers. The quest for stellar parallax - a method for measuring distance to the stars-- began in earnest with Robert Hooke in 1669. He set his sites on Gamma Draconis, the bright star in the head of the constellation Draco, the Dragon, but his result was uncertain. In 1838, Friedrich Bessel solved the problem of measuring stellar distance by focusing on Cygnus 61, a small star in the constellation Cygnus, the celestial Swan. Using a precision instrument called a heliometer, he calculated it to be over 60 trillion miles away.