1. Hertzsprung – Russell Diagram By: Jan Parker | Science Teacher | Hinkley High School | Aurora, CO
2. The Hertzsprung – Russell diagram gives us a way to look at a stars color, temperature, and brightness
3. The Spectral Class refers to color where O stars are "blue", B are "blue-white", A stars "white", F stars "yellow-white", G stars "yellow", K stars "orange", and M stars are "red.” Actual star colors perceived by an observer may deviate from these colors depending on visual conditions and individual stars observed.
4. Notice that as the color changes, so does the temperature. “O” stars – the blue ones – are the hottest, while “M” stars – red ones – are the coolest.
5. One really important idea: the H-R Diagram is NOT a “star chart.” It doesn’t give a map of the stars you would see in the sky. Instead, it plots stars currently in the universe by their color, temperature, and brightness. In other words, as a star goes through its life cycle, it would shift positions on this chart.
6. Let’s look at how that would happen by watching our sun “grow old.”
7. Here is our sun’s position on the H-R diagram today. Our sun – currently a main sequence star – is seen here as a G class star with a luminosity of 1. our sun
8. In about 5 billion years, our sun will begin running of of fuel and will expand while its outer layers become cooler, brighter and red. It will be a Red Giant.
9. The next stage of our sun’s life will happen when the sun runs out of all hydrogen and helium and its atmosphere has dissipated away. Then, what will remain is a dense, white, hot core called a white dwarf. It is colored black here so that it can be seen.
10. Click the picture above to launch a short animation of a star moving through its life cycle.
11. Although there is a stage beyond white dwarfs for stars the size of our sun, that stage – the black dwarf – would not be shown on this chart. Why do you think that is?
12. A black dwarf is a hypothetical star remnant created when a white dwarf becomes sufficiently cool so as to no longer emit significant heat or light. Since the time required for a white dwarf to reach this state is calculated to be longer than the current age of the universe of 13.7 billion years, no black dwarfs are expected to exist in the universe yet
13. So, black dwarfs wouldn’t be shown on this chart because they emit no light, and would give off very little radiation (heat).
click to bring up explanation – as students are reading (or as your are reading aloud) the colors of the spectral class will fade in (3 seconds after you click)
click to bring up explanation
covers the common misconception that the H-R diagram is a star chart
click once to bring in text, click again and our sun appears on H-R diagram
click image in middle to launch animation
clicking the image brings up a flash activity where students can identify the relative temperature and brightness of different stars/placements on the diagram
14 question quiz is launched when image is clicked
