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ACS - Advanced Camera for Surveys (See Instruments).
Arc minute (am) - See arcsecond.
Arcsecond (as) - For the
measurement of small angles, degrees are too large. 1 Degree
= 60 arc minutes ; 1 arc minute = 60 arc seconds. Further
divisions are possible by using the SI prefixes e.g. mas =
milli arc second or 1/1000th of 1 arc second. The "arc"
in arc second assures that this is a measure of angle, not
time.
Axial Instrument - Science Instruments for HST are
classified according to their shape and how they are mounted
in the telescope. Axial instruments are about the size and
shape of a telephone booth. There are a total of four of these
instruments in HST at any one time. Currently the four axial
instruments are: STIS, NICMOS, FOC and COSTAR. Axial instruments
are mounted in the rear of the telescope along the optical
axis. Light from the telescope's mirrors enters these instruments
directly.
Charge Coupled Device (CCD) - Charge coupled devices
are the detectors used in modern video cameras and in digital
cameras. Like all electronic photosensors, they turn light
(photons) into electric charges (electrons). CCD's have many
characteristics which are desirable for astronomy. A good
CCD has a better dynamic range than film, enabling a CCD based
camera to record many levels of light and dark. CCD's are
linear over much of their range, meaning that the intensity
of the image may be measured. They are fast, and respond to
a wide range of wavelengths (see Electromagnetic Spectrum).
COS - Cosmic Origins Spectrograph (See Instruments).
COSTAR- Corrective Optics Space Telescope Axial Replacement
(See Instruments).
Electromagnetic Spectrum
- Light is an electromagnetic wave. Different colors of light
correspond to different wavelengths. The Hubble Telescope
has instruments which can see wavelengths from Near Ultra-violet
(NUV) to the Near Infra-Red (NIR).
FGS -Fine Guidance Sensors (See Instruments).
Field of View (FOV) -
The field of view of an astronomical instrument is the angular
size of an image. Although the WFC3 instrument will have a
large field of view, this is large compared to other instruments.
The entire field of view of the Hubble telescope is comparable
to the "O" in "One Dime" held at arm's
length. Although this seems like a small area, images from
astronomical targets are frequently smaller than this.
FOC - Faint Object Camera (See Instruments).
Focal Plane - The imaginary surface at which the light
to all of the HST instrument is focused. Also the diagram
which shows how each of the instruments see the sky. The HST
Focal Plane is a familiar sight to many.
FOS - Faint Object Spectrometer (See Instruments).
GHRS - Goddard High Resolution Spectrograph (See Instruments).
Instruments - The Hubble
Space Telescope Program uses many instruments to probe the
heavens. The past, present, and future instruments are:
- ACS
- Advanced Camera for Surveys - The Advanced Camera
for Surveys (ACS) is a third-generation Imaging Camera.
ACS Website.
- COS
- Cosmic Origins Spectrograph - Fourth Generation
Spectrometer. COS is an ultraviolet spectrograph optimized
for observing faint point sources with moderate spectral
resolution COS
Website.
- COSTAR
- Corrective Optics Space Telescope Axial Replacement
- Second Generation Corrective Optics. COSTAR is not
an actual instrument, it consists of mirrors which
refocus the abberated light from the HST optical system
for first generation instruments. Only FOC utilizes
its services today.
- FGS
- Fine Guidance Sensors - Science/Guidance instruments.
The FGS's are used in a "dual-purpose" mode
serving to lock on to "guide stars" which
help the telescope obtain the exceedingly accurate
pointing necessary for observation of astronomical
targets. These instruments can also be used
to obtain highly accurate measurements of stellar
positions.
- FOC
- Faint Object Camera - First Generation Imaging camera.
FOC is used to image very small field of view, very
faint targets. Last first generation instrument on
HST.
- FOS
- Faint Object Spectrometer - First Generation Spectrometer.
FOS was used to obtain spectra of very faint or far away sources.
FOS also had a polarimeter for the study of the polarized
light from these sources.
- GHRS
- Goddard High Resolution Spectrograph - First Generation
Spectrograph. GHRS was used to obtain high resolution
spectra of bright targets.
- HSP
- High Speed Photometer - First Generation Photometer.
This instrument was used to measure very fast brightness
changes in diverse objects.
- NICMOS
- Near Infrared Camera/Multi-Object Spectrometer.
Second Generation Imager/Spectrograph. NICMOS is HST's
only NIR instrument.
- STIS
- Space Telescope Imaging Spectrograph - Second Generation
Imager/Spectrograph. STIS is used to obtain high resolution
spectra of resolved objects. The special ability of
STIS is to simultaneously obtain spectra from many
different points along the target. STIS Website.
- WF/PC
(1) -Wide Field / Planetary Camera -
First Generation Imaging camera. WF/PC operated in
either Wide Field mode, capturing the largest images,
or Planetary mode with higher resolution.
- WFPC2
- Wide Field / Planetary Camera II -
Second Generation Imaging camera. WFPC2 is an upgraded
version of WF/PC (1) which includes corrective optics
and improved detectors. WFPC2
Website.
- WFC3
- Wide Field Camera 3. Fourth Generation Imaging camera.
This camera will supplement ACS
and guarantee imaging capability for HST after the
fourth Servicing Mission.
Near
Infrared (NIR) - See Electromagnetic
Spectrum.
Near Ultra-Violet (NUV)
- See Electromagnetic
Spectrum.
Nanometer (nm) - Wavelengths
of light are extremely small. Units like nanometers (billionths
of meters) are frequently used. Visible light is 400-700 nm.
Radial Instrument - Science Instruments for HST are
classified according to their shape and how they are mounted
in the telescope. Radial instruments are mounted above the
axial instruments and to the side. Radial instruments receive
light by use of "pickoff mirrors" which redirect
the light path into the instrument, rather than directly like
axial instruments. There are a total of four radial instruments
on HST. Three of the radial instruments are the
FGS's and the fourth is WFPC2. WFC3 will replace WFPC2.
Selectable Optical Filter Assembly (SOFA) - This is
the name of the carousel which was removed form WF/PC (1)
and which held the filters used on orbit in this instrument.
By re-using legacy equipment in this way, development costs
are held down for WFC3.
Servicing Mission (SM) - A servicing mission is a
Space Shuttle flight during which repairs and upgrades are
performed on the Hubble Space Telescope. There have been two
Servicing Missions to date, and three more are planned.
Spectrum - If white light is passed through a prism,
it is broken into many colors, like a rainbow, called a spectrum.
The spectrum of a star or luminous source can tell us many
things about it, like temperature, composition, and velocity.
See Electromagnetic Spectrum.
STScI - Space Telescope Science Institute - The STScI
is located in Baltimore, Maryland at the John's Hopkins University.
The STScI maintains all operations for the telescope including
proposal selection, scheduling, data calibration, distribution,
and archiving. Their website can be found here.
WF/PC (1) -Wide Field / Planetary Camera (See Instruments).
WFPC2-Wide Field / Planetary Camera II (See Instruments).
WFC3 -Wide Field Camera 3 (See Instruments).
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