![]() In addition, look at this image: Hubble Space Telescope image of star cluster 47 Tucanae. Note how for the three different objects with three different temperatures, that for the coolest object: its B intensity is smaller than its V intensity, for the warmer object: they are roughly the same, and for the hottest object: its B intensity is larger than its V intensity.Ĭredit: PhET and the Penn State Astronomy & Astrophysics When you click the play button, you see an animated curve representing blackbodies of different temperatures, and it marks the B and V measurements through these two filters for the different blackbodies. Intensity, There is a yellow band showing the frequency range that corresponds to the V filter, and a blue band that illustrates the frequency range for the B filter. The animation below shows a plot of Frequency vs. The difference between these two, B-V, is the star’s color. The B filter measures the star’s brightness in blue light, and the V filter measures the star’s brightness in yellow light. They then re-observe the same star with a visual (V), or yellow, filter. To do this, they put a blue filter (B) on the telescope and observe the star. Measuring a star’s spectrum is not always easy, but astronomers can often measure a star’s color reasonably easily. For example, a 4500 K blackbody peaks in the red part of the spectrum, a 6000 K blackbody in the green part of the spectrum, and a 7500 K blackbody in the blue part of the spectrum. ![]() If you study this plot, or one of the interactive blackbody radiation demonstrators we used in the last lesson, you can prove to yourself that the color of a star provides a fairly accurate measurement of its surface temperature. ![]()
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