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Click here to start Stella, or the image to the right.
Towards the upper right of the star field, you can see a group of stars. Farther to the right, by the edge of what you can see, is another bright star.
Point the telescope at it by clicking there. It should look like this:
The blue banner across the top should tell you that you are pointing at star S106.
Another way to point the telescope: See the green box above the star field? Type 101 in this box and press TAB or ENTER. The telescope moves over to star S101.
Point back at S106, over on the right. Let’s study star S106
The star we are pointing at appears pretty bright compared to some others. But is it really bright, or just closer to Earth? To find out, click the Photometry tab, and…
...Leaving the filter set at None, click the 1 sec button. You just measured the brightness of S106! You can see the results on the screen. Your measurement has two parts: S106 and sky. Think about what that might mean
In the toolbar, find the Tables button and choose Photometry. (See the left-hand illustration below.) A table appears with your measurement. You may have to stretch it to see the whole table. (Right side below.)
The Photometry table shows that every observation has two parts: we measure the brightness of the “target”—in this case, the star S106—and we also measure the brightness of the “sky” nearby. In this case, S106 is so bright that the sky is almost zero by comparison. For a faint star, these two numbers might be closer, so to get the actual brightness of the star, you would have to subtract.
Take another measurement, again using the 1 sec button. See how the new measurement appears in the table. Also notice how the date has increased. Time is passing.
Take more measurements (like, 30 of them). Notice how the numbers are changing? Is this a “real” change in the brightness of the star, or a random fluctuation? Let’s make a graph to find out.
Click Graph in the toolbar. An empty graph appears.
Drag date(yr) from the column heading to the horizontal axis and count to the vertical. Your graph might look something like the illustration.
Which points are which? You can probably figure it out by looking at the values, but try selecting points in the graph. The table will show you which points you have selected.
You should see that the points around 50,000 are all “target,” and the ones near the axis, near zero, are “sky.” That is, the star is bright and the sky is dark.
Drag obs from the table’s column heading to the middle of the graph. This creates a legend. Now you can tell which are target and which are sky.
Apparently, S106’s brightness is changing over time. It’s a variable star.
Determine the period of S106’s variation.
Determine the amplitude of S106’s variation.
Create a graph when you measure S106 using buttons other than the 1 sec button.
Using the color filters, determine the 'Blueness' of S106. This would be a relative color compared to 'Red'.
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