Determining the age of a star or planet can be as hard as guessing the age of a person who looks exactly the same from childhood to retirement.
Sussing out a star’s age
Fortunately, stars change subtly in brightness and color over time. With very accurate measurements, astronomers can compare these measurements of a star to mathematical models that predict what happens to stars as they get older and estimate an age from there.
A star’s spin also generates a strong magnetic field and produces magnetic activity, such as stellar flares – powerful bursts of energy and light that occur on stars’ surfaces. A steady decline in magnetic activity from a star can also help estimate its age.
A more advanced method for determining the ages of stars is called asteroseismology, or star shaking. Astronomers study vibrations on the surfaces of stars caused by waves that travel through their interiors. Young stars have different vibrational patterns than old stars. By using this method, astronomers have estimated the Sun to be 4.58 billion years old.
Piecing together a planet’s age
In the solar system, radionuclides are the key to dating planets. These are special atoms that slowly release energy over a long period of time. As natural clocks, radionuclides help scientists determine the ages of all kinds of things, from rocks to bones and pottery.