ClassX Video Lessons Stellar Classification 101: Types of Stars and the History of Their Classification 101
Stars are amazing objects in the sky that light up our night. They are like the building blocks of galaxies and play a big role in creating new elements. Even though stars might look similar to us, they are actually very different from each other. By studying stars, scientists can learn a lot about the history of the universe.
Long ago, people noticed that some stars were brighter than others. At first, they thought this was a good way to tell stars apart. But just like a flashlight looks dimmer when it’s far away, stars can look different depending on how far they are from Earth. When telescopes were invented, astronomers saw that stars came in different colors like blue, white, yellow, orange, and red. However, it was hard to agree on a system to classify them just by color.
The real breakthrough came with a tool called spectroscopy. This tool breaks light into different colors, just like a rainbow. Scientists found out that stars have dark lines in their light, called absorption lines. These lines happen when gases in a star absorb certain colors of light. By studying these lines, astronomers could figure out what stars are made of and group them by their characteristics.
In 1872, Henry Draper started taking pictures of stars’ light. After he passed away, Edward Pickering and a group of women called the Harvard Computers continued his work. Annie Jump Cannon, one of these women, created a simpler way to classify stars based on their temperature. She used letters O, B, A, F, G, K, and M to group stars, with O being the hottest and M the coolest. Our Sun is a G-type star, which means it’s in the middle of the temperature scale.
The Hertzsprung-Russell Diagram, or HR Diagram, is a special chart that helps classify stars by their brightness and temperature. Most stars fall along a line called the “main sequence,” where they spend most of their lives turning hydrogen into helium. This line goes from the top left (hot and bright stars) to the bottom right (cool and dim stars).
When stars run out of hydrogen, they become giants or supergiants. These stars are bigger and brighter and are found above the main sequence on the HR Diagram. After using up their fuel, smaller stars like our Sun become white dwarfs, which are small, dense, and cool over time.
Some stars don’t fit neatly into the HR Diagram. Supergiants can explode in a supernova, turning into black holes or neutron stars. Neutron stars are very dense and have strong magnetic fields. Pulsars, a type of neutron star, send out beams of light that we can see from Earth. Brown dwarfs, or “failed stars,” are too small to shine like regular stars and are hard to see because they mostly give off infrared light.
Classifying stars is a complex task that involves looking at their color, size, brightness, and life stages. Our Sun is a G-type star on the main sequence, but there are many different kinds of stars out there. By understanding these classifications, astronomers can learn more about the universe and the fascinating stars that fill it.
Star Color Observation: On a clear night, go outside with an adult and observe the stars. Try to notice the different colors of the stars you see. Are some stars more blue, white, or red? Draw a picture of the night sky and color the stars you observed. Discuss with your family why you think stars have different colors and what that might tell us about their temperature.
Create Your Own HR Diagram: Use colored paper or crayons to create a simple Hertzsprung-Russell Diagram. Cut out stars of different colors and sizes to represent different types of stars (e.g., blue for hot stars, red for cool stars). Arrange them on a large piece of paper to show the main sequence from hot and bright to cool and dim. Label your diagram and share it with your class, explaining what each color and size represents.
Star Life Cycle Story: Write a short story about a star’s life. Start with the star being born in a nebula, then describe its life on the main sequence, and finally, what happens when it becomes a giant or supergiant. Use your imagination to describe what it might be like to be a star, and include details about its color, size, and brightness at different stages. Share your story with a friend or family member and discuss how stars change over time.
