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Planetarium Activity

Turn off the daylight and horizon displays. Open the “Display” Palette on the vertical toolbar and turn on the NGCIC display. Then click on the left side of the NGC-IC button. This will open a window with options about displaying NGC and IC objects. Under “Which objects to draw” be sure Open Cluster is turned on (as indicated by a check mark in its box). Click Apply and then OK. Use the “Selection” button and click on “Find.” In the window, type in NGC 1981 and then click Find. The display will move to the location of NGC 1981, an open cluster near the Orion Molecular Cloud. Zoom in until the circle around the cluster nearly fills the display. As you zoom in, be sure to notice the Orion Nebula. Using the Selection Tool, double click on the dozen or so brightest stars, one at a time, to open the Info Window. Record the temperatures of the stars. O and B stars are hotter than 10,000 K. What fraction of the bright stars in NGC 1981 are O and B stars? Repeat the process for two other open clusters, NGC 752 and NGC 1502. How does the fraction of O and B stars you found in NGC 1981, near the Orion Nebula, compare with the fraction in the other clusters? What do you think these stars have to do with the visible light from the Orion Nebula?

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