In this segment of our video book, we take a close look at light in order to understand the Hertzsprung - Russell diagram.
We explain that by distant star, we mean a star too far away for parallax distance measurements. We then go into the dual nature of light as both a particle and a wave. Viewing light as a wave, we cover the full electromagnetic spectrum, followed by blackbody radiation. Then using known luminosity from nearby stars, we map star color to temperature and star temperature to luminosity – the basic H-R Diagram.
To give this diagram meaning, we introduce the nature of nuclear fusion and how star color and temperature are related to the mass of the star. This gives us the meaning behind the main diagonal line on the H-R Diagram – it represents the main sequence for stars burning Hydrogen. We follow by describing the end-of-life process for stars that moves them off the main sequence and into the realm of giant and supergiant stars. This gives meaning to the two collections of stars above the main sequence. Finally, we discuss the cataclysmic explosion at the end and how this leaves behind White Dwarfs.
Once the meaning of the H-R Diagram is understood, we use spectral analysis to determine a star’s place on the diagram. We use a stars color, temperature and spectral class to determine its place on the horizontal axis. We use spectral absorption lines and Luminosity Classes to determine its place on the vertical axis. This gives us its intrinsic luminosity and thereby its distance.
We then use this new technique for determining distance to distant stars V1331 Cyg, UY Scuti, WR 124, and AG Carinae.
Next cover Delta Cephei a variable luminosity star, and Henrietta Leavitt’s work mapping the period of a Cepheid star’s luminosity cycle to the star’s luminosity. This gave us our first “Standard Candle”. RR Lyrae came as the next standard candle variable.
We go on to cover Zeta Geminorum, Eta Aquila, HIP 13044, T Lyrae, SDSS J102915+172927, Mu Cephei, HE 1523-0901, Eta Carinae, V838 Monocerotis, AW Cyg, extra galactic Hypervelocity Star HVS 2v, and HE 0437-5439 a star that is being ejected from the galaxy possibly via a close encounter with the Milky Way’s central supermassive black hole.
We conclude with the major new distance ladder rungs: the H-R Diagram, along with Cepheid variables and RR Lyrae variables as “standard candles”.