The downside of this method is that cepheids are not very common. Absolute magnitude is the measure of a celestial object's intrinsic brightness. Trigonometric parallax: By measuring the apparent motion of nearby stars against the background, we can directly calculate their distances. Combining our parallax angle and another distance we already know gives us all we need to know about our triangle: You need to cut the parallax in half to get the right measurement. Alpha Centauri: parallax angle of 0.7420 arcsecond. Sample task: convert 5 light years to parsecs. window.jQuery || document.write('