Comet Labs WN591 Bedienungsanleitung PDF herunterladen (Seite 10)

Help! There is a comet in my computer! 7

2 Detection of emitted light

Our eyes, supported by our brain, are amazing instruments. We process incredible amounts

of visual information and store a lot of what we see in our memory. We can see very small

details. We can focus to near and far objects. There is one problem with our eyes, though –

we are not very good at judging the quantitative aspects of all the information we receive.

By only looking, we cannot tell whether two similar pencils located at different parts of a

table are of the same length or not, or how many centimetres they have. We are even worse

at measuring light intensities with our eyes. When we walk into a dimly-lit room from

sunshine, it seems to be very dark. A few moments later, we see perfectly well. When

observing a comet slide under a microscope, we cannot say how much light comes from

the head and how much from the tail. Our eyes are also not sensitive enough to see very

weak light.

We need to use technology for precise measurement of the intensity of light emitted from

comets. We can direct the emitted light through a microscope to a device that can detect

light intensity - a camera can do this (Figure 2C). A detector located in the camera is

composed of a rectangular array of small light-sensitive elements. The size of each detector

element is only a few micrometers across. Each element converts the measured light

intensity to a digital format, i.e. to numbers. By definition, small numbers represent a low

light intensity (few photons hit the detecting element), and high numbers a high light

intensity (many photons hit the detecting element). If we now connect the camera to a

computer and record the image, the camera sends the numbers representing each detector

element together with its coordinates on the detection array to the computer. The camera

sends all numbers representing one image as a package of digital data (an image file). The

computer decodes the received digital (numerical) information and displays it as an image

on the monitor screen (Figure 3A).

An image is composed of small dots called pixels. Each pixel represents one light-

sensitive element of the camera, and the numbers corresponding to light intensity

detected for each pixel are stored in a computer file.

We will use a simplified model image of a comet (Figures 3B, 3C) to explain how the

comet intensity is measured. This image was generated artificially and has extremely large

pixels for easier explanation of the discussed procedures.

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Comet Labs WN591 Bedienungsanleitung Seite 10