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--- courses:phy100:3 [2023/06/21 03:13] – asad
+++ courses:phy100:3 [2023/06/22 11:41] (current) – [5. Seeing the invisible] asad
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 This is the 'spectrum' of sunlight, meaning the light of the sun at different colors. Note that this spectrum is not the same as the spectrum you saw in the beginning of this section. The previous spectrum was smooth, that did not have any black lines and showed all the shades of all the seven colors. But some shades of some of the colors are missing in this spectrum. There are hundreds of such 'missing colors' and only a few prominent missing colors (called '**absorption lines**') have been identified here using the letters A, B, C, D, E, F, G, H and K.
-Why are some colors (light at some wavelengths or frequencies) missing? The sun emits smooth light, meaning it emits light at all colors from violet to red. But the sun has an atmosphere where there are many different chemical elements. The elements **absorb** light of specific colors. Each element can only absorb the light of one specific color. Each line correspond to the absorption of light at a specific color by a specific element. So the lines directly tell us which elements are present in the atmosphere of the sun.
+Why are some colors (light at some wavelengths or frequencies) missing? The sun emits smooth light, meaning it emits light at all colors from violet to red. But the sun has an atmosphere where there are many different [[un:chemical element]]s. The elements **absorb** light of specific colors. Each element can only absorb the light of one specific color. Each line correspond to the absorption of light at a specific color by a specific element. So the lines directly tell us which elements are present in the atmosphere of the sun.
 A and B lines are created by oxygen molecules, C lines by hydrogen atoms, D by sodium, E by iron, and G, H and K by calcium. So the dark 'absorption lines' or the 'missing colors' give away the chemical composition of stars.
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 ===== - eVscope and eQuinox =====
-In this course, you will use an eQuinox telescope made by Unistellar for your final project. Unistellar makes two models: eVscope and eQuinox. The eVscope has live projection system in place of an eyepiece so that people can have sneak-peek of what the telescope is observing. The eQuinox does not have any eyepiece or live projection system. Both models work in a similar way. The telescope creates a WiFi network that you connect using your phone. Then you can open the 'Unistellar' app on your phone and control and move the telescope using the app. The field of view of the telescope always visible on the app and you can capture an image whenever you want.
+In this course, you will use an eQuinox telescope made by Unistellar for your final project. Unistellar makes two models: eVscope and eQuinox. The eVscope has a live projection system in place of an eyepiece so that people can have a sneak-peek of what the telescope is observing. The eQuinox does not have any eyepiece or live projection system. Both models work in a similar way. The telescope creates a WiFi network that you connect to using your phone. Then you can open the 'Unistellar' app on your phone and control and move the telescope using the app. The field of view of the telescope is always visible on the app and you can capture an image whenever you want.
 {{:courses:phy100:evscope.jpg?nolink|}}
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 ===== - Seeing the invisible =====
-There are light waves beyond ultraviolet at the high-frequency end and beyond infrared at the low-frequency end. Heinrich Hertz detected such a wave for the first time and named 'x-ray' as it was unknown as of then. Later many more '**invisible**' light waves have been found. We use microwave light for heating our food and watching TV and we use radio waves for all kinds of wireless communication and the all-important Global Positioning System (GPS).
+There are light waves beyond ultraviolet at the high-frequency end and beyond infrared at the low-frequency end. Heinrich Hertz detected such a wave for the first time and named it 'x-ray' as it was unknown then. Later many more '**invisible**' light waves have been found. We use microwave light for heating our food and watching TV and we use radio waves for all kinds of wireless communication and the all-important Global Positioning System (GPS).
 {{:courses:phy100:waves.jpg?nolink&500|}}