Barnard's Star has a mass of about 0.14 solar masses (), and a radius 15% to 20% of that of the Sun. Thus, although Barnard's Star has roughly 150 times the mass of Jupiter (), its radius is only 1.5 to 2.0 times larger, due to its much higher density. Its effective temperature is 3,100 kelvin, and it has a visual luminosity of 0.0004 solar luminosities. Barnard's Star is so faint that if it were at the same distance from Earth as the Sun is, it would appear only 100 times brighter than a full moon, comparable to the brightness of the Sun at 80 astronomical units.