Differences

This shows you the differences between two versions of the page.

--- courses:phy100:3 [2023/06/21 02:51] – [5. Seeing the invisible] asad
+++ courses:phy100:3 [2023/06/22 11:41] (current) – [5. Seeing the invisible] asad
@@ Line 2: / Line 2: @@
 ===== - Light =====
-Light can be described both as a **particle** and a **wave**. Light is made of particles called **photons** and waves called **electromagnetic waves**. Let us try to understand light as a wave first.
+Light can be described both as a **particle** and a **wave**. Light is made of particles called **photons** and (at the same freaking time) waves called **electromagnetic waves**. Let us try to understand light as a wave first.
 The best way to visualize a wave is to use the example of a //water wave//. In the following video, you see the largest replica of an ocean created inside a huge dome by US Navy. They use this indoor ocean the size of a football field for experimenting with the effect of waves on oceangoing ships.
@@ Line 60: / Line 60: @@
 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.
@@ Line 90: / Line 90: @@
 ===== - 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|}}
@@ Line 102: / Line 102: @@
 This telescope does not enlarge the image but rather, like all modern telescopes, take high-**resolution** pictures of various objects of the sky. If it has high resolution, you can always zoom in using a computer and see more details of the object. The 'zooming in' is almost like the modern equivalent of the optical 'magnification' used in the olden days.
-The '**field of view**' (FoV) of the telescope is around 0.5 degrees, that is the size of an image taken by eVscope or eQuinox is around 0.5 degrees, almost same as the size of the sun or the moon as viewed from earth. You hide the moon completely using your pinkie, that means 0.5 degrees is the size of your pinkie, the little finger.
+The '**field of view**' (FoV) of the telescope is around 0.5 degrees, that is the size of an image taken by eVscope or eQuinox is around 0.5 degrees, almost same as the size of the sun or the moon as viewed from earth. You can hide the moon completely using your pinkie, that means **0.5 degrees (30 arcminutes)** is the size of your pinkie, the little finger.
 ===== - 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|}}