The sun is a very stable star in the prime of its life. Many stars fluctuate periodically and are called variable stars. Astronomers use cameras to do photometry to precisely determine the stars’ brightnesses. For some stars, this variation can be seen with just your eyes.
The star in the left shoulder of the constellation Orion, the Hunter, is called Betelgeuse. It has been in the news lately because it is currently fainter than it has been in the past. Betelgeuse is a red giant star that is approaching the end of its life with a fluctuation period of about 425 days. It can be almost as faint as Bellatrix (right shoulder, magnitude 1.55) and brighter than Rigel (right knee, magnitude 0). Currently it is at magnitude 1.5.
Come to the observatory on the first Friday each month from sunset-10 p.m. This is the season to see Betelgeuse: humbleisd.net/observatory.