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How small is one arcsecond compared with one degree?

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Diagram illustrating how astronomers calculate the distance to a star using parallax: Earth is shown in two positions on opposite sides of its orbit around the Sun, with lines extending to a nearby star X and further to distant background stars. The apparent shift in star X's position, measured as angle A, is used to determine its distance, with the baseline labeled as 186,000,000 miles. — Parallax Calculating stellar distances.

One arcsecond is a very small unit of angular measurement, defined as exactly 1/3,600 of a degree.1

In the context of parallax, this unit is essential for measuring the immense distances to stars. Because the shift of a star against the background is so slight, astronomers rely on these tiny increments to calculate distance; for example, a star with a parallax of one arcsecond is located at a distance of one parsec, or approximately 3.26 light-years. To visualize how small this angle is, one arcsecond is roughly equivalent to the width of a human hair viewed from 10 meters (33 feet) away.1