SkyGazer_MainSequence_SG4

# SkyGazer_MainSequence_SG4 - Voyager Sky Gazer Magnitudes...

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Voyager Sky Gazer: Magnitudes and the Main Sequence Print out this sheet and follow the instructions, filling in answers on the sheet as you go. When you are done, log onto the course web site at and type the answers you have written down into the Exercise 8 form in the Lessons area on Angel. This week’s Sky Gazer exercise is designed to prepare you for the next lab, in which you will measure the age of the Pleiades star cluster using the CLEA software. That lab requires some familiarity with both the H-R diagram and the magnitude system for representing the brightness of stars. The H-R diagram should be familiar to you from the ISP 205 lecture class. It is basically a graph showing the temperatures of stars along the horizontal axis and the luminosities of stars along the vertical axis. To plot a star’s position on the vertical axis, you need to know its luminosity, which you can determine from the star’s distance and apparent brightness. To plot a star’s position on the horizontal axis, you need to know its surface temperature, which you can determine from its color or spectral type. In an H-R diagram like the one below, all stars undergoing hydrogen fusion in their cores fall along a line called the main sequence.

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In this week’s lab, you will be plotting stars belonging to the Pleiades star cluster in an H- R diagram, but that H-R diagram will look a little different from the one on the previous page. Instead of showing surface temperature on the horizontal axis, it will show spectral type.
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