What is light?

Line vs Continuous

Line spectra

Diagram illustrating the use of spectra to determine stellar rotation. At top left is a white disk representing a non-rotating star as seen from above one of its poles. Three equally wavy arrows point downward, representing light emitted from this star, headed toward Earth. Immediately below the wavy arrows is a spectrum with one narrow absorption line in the middle. Below the spectrum a graph is shown, with luminosity on the vertical axis and wavelength on the horizontal. A curve is plotted which begins as a horizontal line about 3/4 of the way up the luminosity scale then dips sharply downward to near zero luminosity and then back up again to the original horizontal level. This sharp, narrow, and deep line is indicative of no or very slow rotation. On the top right another white disk is shown, with a circular arrow within, indicating its rotation. The left side of the rotating star is moving toward the observer, and the right hand side is moving away. The three wavy arrows are different than those for the non-rotating star. The rotating star’s left-most arrow has many waves representing short (blue) wavelengths, its central arrow has fewer waves, and the right-most arrow has the least waves representing long (red) wavelengths. The spectrum of the rotating star has a much broader absorption line. The rotating star’s graph also plots luminosity versus wavelength, but its curve is much broader and less deep than the non-rotating star.

Doppler effect

What can we learn by analyzing starlight?

Vision and color perception

Color Arithmetic


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