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We call the wavelengths between 400-700
nm the "visible" spectrum. These wavelengths
are what the human eyes are sensitive to. Visible light
is commonly remembered by the anagram ROY G BIV. This
stands for Red, Orange, Yellow, Green, Blue Indigo, and
Violet. These colors are just light at different wavelengths
that the eye interprets as different colors.
Red: 780 nm, Orange: 620 nm, Yellow:
585 nm, Green: 570 nm,
Blue: 490 nm, Indigo: 440 nm, Violet: 420 nm
This "visible" spectrum is just a small part of
the wavelengths that are out there. All wavelengths are collectively
known as the electromagnetic spectrum. :: More
information on light and the electromagnetic spectrum ::
CCD's are able to see a much broader range of wavelengths
than humans can see (Silicon:: 200-1200 nm) enabling astronomers
to observe things not visible to the eye.
Another benefit of CCD's versus the human eye is the CCD's
can take a long exposure. CCD's can absorb data for very long
periods of time, capturing more data. Eyes can only absorb
data (photons) for a short period of time, giving eyes high
refresh rates. The refresh rate is the amount of times aa
image is repainted or refreshed per second on a display (ie
monitor, tv, eye, etc.)
Film has a different set of shortcomings in comparison with scientific CCD's.
CCD cameras are up to 100 times more sensitive than film **.
CCD's also have a greater dynamic range, capturing both faint
and bright details in a single exposure. Film's dynamic range
varies by the film speed.
CCD's also are able to save time. In order to use film for
data analysis the picture first needs to be taken, then developed,
then digitized, before it can be analyzed. Information from
a CCD is in digital form so analyzing can happen quicker.
Another benefit of CCD's is the ease of use. Retriving film
from an orbiting telescope can be quite difficult.
** CCD's come in different qualities. Astronomical
CCD's are higher quality than the CCD's that are in consumer
digital camera. Film has a better dynamic range than most
ccd's in consumer level digital camera .
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