How do people know how old a star is?
Wow, this is a popular question! Scientists have learned a lot about stars, especially the stages in their lives. Since a single star can live for billions of years, scientists study several stars at different stages of their lives.
Certain characteristics of stars are related to each other. The luminosity, temperature, magnitude, spectral class and mass are all related. For example, larger stars are cooler, red in color and are very luminous. All these characteristics are important in determining the age of a star, but scientists found that the composition of a star is the most important.
The Hertzsprung-Russell Diagram is a very famous diagram that shows how these characteristics of stars are related. Stars are divided into different categories depending on their temperature, size, etc. Most stars are either, main sequence, or giants. Scientists realized that the compositions of stars were related to the diagram. Stars spend most of their lives as a main sequence star. During this time they burn hydrogen in their core.
When a star burns hydrogen it creates helium. At some point the star uses up all the hydrogen, and starts to burn helium. The star expands and cools while burning the helium. During this stage a star is called a giant.
So why tell you all of this? Well, scientists discovered this is a very easy way to compare stars. It is also a great way to tell the age of a star. Scientists can look at the spectra of a star and tell its temperature, which is related to the size, etc. In turn, this information reveals how much hydrogen or helium is left inside the star. We know the rate at which stars burn the gases. Scientists can now tell how old the star is depending on its composition!
Submitted by Dana, Kelly, Michael, Kelli, Tommy, Nick, Randall, (ages 11 &12, North Carolina)
Windows original artwork
Shop Windows to the Universe Science Store!
Learn about Earth and space science, and have fun while doing it! The games
section of our online store
includes a climate change card game
and the Traveling Nitrogen game
You might also be interested in:
Most stars fall on a rather wide line (highlighted in red) that passes from the lower right to the upper left of the page. This line is called the main sequence. It tells us interesting things about how...more
Follow along the horizontal curves (highlighted in red). These are the locations of the giant stars. Giants don't behave like main sequence stars. The brightness is constant or even increasing as you...more
It depends on which type of motion you are asking about. If you take a birds-eye view from the top of the solar system all the planets orbit around the Sun in a counter-clockwise (or direct) direction....more
Almost everyone has a question or two about living in space. What do astronauts do in space? How do they do everyday things like eat, sleep and go to the bathroom? It's important to note that astronauts...more
There is a really neat internet program called Solar System Live that shows the position of all of the planets and the Sun for any given day. If you go to that page, you'll see an image similar to the...more
The picture of the American Flag (the one put there by the Apollo astronauts) is waving (or straight out) in the wind. How could that be possible if there is no atmosphere on the Moon? Was it some sort...more
I was wondering if there is a new planet? Are there planets (a tenth planet?) after Pluto belonging to our solar system? What are the names of the new planets discovered in the solar system? Are there...more
If that is so, the energy released during the Big Bang must have created many such black holes. Therefore most of the Energy of the Big bang must have disappeared in that form. Then how did the Universe...more