Friedrich Bessel... achieved a breakthrough. Please hold your thumb at arm's length and alternate closing your left and right eyes a few times. ...[Y]our thumb appears to jump left and right by a certain angle relative to the background... [M]ove your thumb closer... and you'll see this jump angle growing. Astronomers call this jump angle parallax... [W]e can... compare telescopic photographs taken six months apart, when Earth is on opposite sides of the Sun. ...Bessel noticed ...61 Cygni ...moved a tiny angle, revealing its distance to be almost a million times that to the Sun... Now that Bessel knew the distance he used... [the] inverse-square law to figure out how luminous it was... in the same ballpark as the Sun... Giordano Bruno had been right after all!