- 3966 -
HUBBLE - images early galaxies. -
Since its launch in 1990, the Hubble Space Telescope has made more than
one million observations of the universe,
broadening humanity's knowledge of the cosmos almost immeasurably.
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------------ 3966
- HUBBLE -
images early galaxies.
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----------------------------- Picture
spiral galaxy
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- The spiral
galaxy “UGC 2890” appears side-on in this image from the Hubble Space
Telescope, with bright foreground stars studding the image. This galaxy, which
lies around 30 million light-years away in the constellation Camelopardalis,
hosted a powerful supernova explosion that astronomers observed in 2009.
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- Hubble
doesn't see the universe as we do. The telescope views the cosmos across a
broad range of light wavelengths, some of which our eyes are incapable of
seeing.
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- If we
looked out across space with our own eyes, not only would we not see much of
what Hubble sees, but a great deal of what we do see would look very different
from the images delivered to us by the Hubble space telescope.
- How is the
data this pioneering space telescope collects turned into stunning visuals that
we can see, understand and marvel at, and how much of this imagery is "real?
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- Hubble has
two primary camera systems which the telescope uses to observe the universe
from its position roughly 332 miles above Earth's surface. Working in unison, the Advanced Camera for
Surveys (ACS) and the Wide Field Camera 3 (WFC3) are able to provide
astronomers with wide-field imaging over a broad range of wavelengths.
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- Both camera
systems were installed on Hubble by spacewalking astronauts after the
observatory's April 1990 launch aboard the space shuttle Discovery.
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- ACS joined
Hubble in 2002 and was designed primarily for wide-field imagery in visible
wavelengths. The ACS system is composed of three cameras or
"channels" that capture different types of images.
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- Two of
those channels became inoperable in 2007 due to an electronics failure.
Astronauts were able to repair one of the cameras two years later, restoring
the ability of ACS to take high-resolution, wide-field pictures.
That 2009 repair was performed during Hubble's
Servicing Mission 4, which also installed the WFC3 system, now the telescope's
main imager. The space telescope's
previous cameras include the Wide Field and Planetary Camera, the Wide Field
and Planetary Camera 2, the High-Speed Photometer and the Faint Object Camera.
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- Among
Hubble's total of six instruments are its two spectrometers, the Cosmic Origins
Spectrograph (COS), and the Space Telescope Imaging Spectrograph (STIS).
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- The
spectrometers break light down so its component parts can be seen. Because
elements and chemicals emit and absorb light at characteristic wavelengths,
Hubble allows astronomers to learn about the composition of the objects.
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- One of the
advantages that Hubble has as it zooms around Earth about 15 times each day is
that it can pick up wavelengths of light that would normally be absorbed by our
planet's atmosphere. The telescope's
7.8-foot-wide primary mirror collects an immense amount of light across a wide
range of wavelengths that ground telescopes can't see and curves it toward the
telescope's instruments and cameras.
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- Hubble's
cameras can see the universe from the infrared region of the electromagnetic
spectrum through visible light wavelengths all the way up to ultraviolet light.
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- The primary
capabilities of the telescope are in the ultraviolet and visible parts of the
spectrum from 100 to 800 nanometers, though the telescope can also see light
with wavelengths as long as 2,500 nanometers.
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- ACS is used
predominantly to collect light in visible wavelengths but is also capable of
seeing ultraviolet and near-infrared light.
WFC3 provides wide-field imagery in ultraviolet, visible and infrared
light. COS focuses exclusively on
ultraviolet light and is considered the most sensitive ultraviolet spectrograph
ever built.
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- COS has boosted
Hubble's sensitivity by a factor of at least 10 in the ultraviolet spectrum,
resulting in a net 70-times sensitivity boost when looking at very faint
objects.
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- Hubble sees
the universe in many different "shades of gray." Viewing the cosmos
in what to us looks like monochrome, Hubble is capable of highlighting subtle
differences in the intensity of light at different wavelengths, which helps
scientists understand physical processes and the composition of objects.
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- Observing
ultraviolet light is looking at extremely faint objects and single points of
light, like stars and quasars. Seeing in infrared, on the other hand, is vital
for the examination of very distant objects that existed in the early history
of the universe.
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- Because, as
light travels from these faraway objects, the expansion of the universe
"stretches" its wavelengths. This process is called
"redshifting," because longer wavelengths of light in the visible
spectrum are red (compared to blue at the shorter end).
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- The longer
this light has been traversing the universe, the more extreme the redshift of
its wavelength. This means that ancient objects that emitted visible light are
now better seen in long-wavelength infrared light.
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- Hubble's
ability to study such stretched light from early stars has allowed scientists
to better constrain the age of the universe, to around 13.8 billion years.
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- The earliest
and most distant object Hubble has been able to image thus far is the highly
redshifted galaxy GN-z11, which is located about 13.4 billion light-years away.
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- The wider
range of wavelengths that Hubble can observe also means that it won't be
replaced by NASA's new James Webb Space Telescope (JWST). Despite being the
most powerful telescope humanity has ever put into orbit, JWST is mostly
limited to highly detailed observations in infrared light, with Hubble seeing
less clearly but over a much wider spread of the electromagnetic spectrum.
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- This
ultimately means that JWST and Hubble make an excellent team observing the
cosmos.
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- Human eyes
only see a small fraction of the electromagnetic spectrum that slots between
infrared light and ultraviolet light, from about 380 to 700 nanometers. So,
most raw images produced by Hubble look black and white to us.
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- The
colorization of Hubble's "raw" grayscale images isn't for purely
aesthetic reasons, however. Some
images show "true" colors, while others feature hues that are
assigned to represent wavelengths of light that human eyes can't see. These
color composite images are generally created by combining exposures captured by
Hubble using different filters.
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- A different
color is assigned to each filter, with that color corresponding to the
wavelength the filter allows through. So, the long-wavelength filter image is
represented in the composite by red, the medium wavelengths by green and the
shortest wavelengths by blue.
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- Colors
might be added to Hubble photos to represent specific chemical elements present
in or around the imaged object. Such color processing can reveal a wealth of
scientific information that isn't present in grayscale raw images from Hubble.
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- Images are
also processed to remove imperfections and effects that don't come from the
objects being observed by Hubble. These undesired features could be the result
of aging sensors causing "dead pixels" in images or the dynamic
environment of space.
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- Hubble
images can be streaked by lines of bright light caused by passing asteroids,
satellites or even flashing cosmic rays. The Hubble team often removes such
distractions before releasing an image to the public.
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- In addition,
larger mosaics made of many Hubble images stitched together must have gaps
removed to create a single unified image. Hubble image processors also have to
decide how to orient images, as there is no actual "up" or
"down" in space.
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- The
processing of Hubble images is an intricate and time-consuming procedure. Even
simple Hubble photos can take days to process, while large complex mosaics of
multiple images can take months. Now you
know the rest of the story.
-
April 20, 2023 HUBBLE
- images early galaxies. 3966
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--- Thursday, April 20, 2023 ---------------------------
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