Anyone looking up to the night sky will notice that it is a dynamic scene. Due to the earth’s rotation, stars appear to move from east to west, just like the sun and the moon. The occasional shooting star, a piece of debris burning up as it enters earth’s atmosphere, is a familiar sight. Satellites appear and disappear suddenly, particularly close to sunset and sunrise, as they exit and enter earth’s shadow respectively. And stars appear to twinkle, changing slightly in brightness and, on some nights, significantly changing their apparent colour rapidly as well. Do stars really change appearance?

The answer is no – stars are relatively stable objects, only changing brightness gradually – normally over millions of years, but this can be over a matter of days for stars known as variable stars. Colour changes are normally only due to changes in the phase of a star’s life, which processes take millions or billions of years to occur. The reason we see stars twinkling is only because of the presence of the earth’s atmosphere, which interferes with the propagation of light in a process called atmospheric refraction. Indeed, for example on particularly hazy nights, it is common to see a more pronounced twinkling effect. For astronauts on board the ISS, for example, stars do not twinkle at all.