Parallax demonstration. Woman holding one finger in front of her eye and another at arm's length and then observing them through one closed eye at a time, to demonstrate a parallax. If the fingers are aligned when viewed through the first eye, when viewed through the other eye, they will be out of alignment. This difference in apparent position is known as parallax. It is measured by calculating the angle between the two lines of sight. The closer an object is, the larger its parallax when observed from different positions. Therefore, the parallax can be used to determine distance. It is frequently used to measure the distance of stars and other objects outside of our Solar System.