Fine Guidance Sensor / Near Infrared Imager and Slitless Spectrograph (FGS/NIRISS) - NASA Science
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FGS/NIRISS
Fine Guidance Sensor / Near Infrared Imager and Slitless Spectrograph (FGS/NIRISS)
Instrument
Quick Facts
FGS is a guider that locks on to bright stars in deep space to keep Webb on target creating sharp high quality images.
FGS allows Webb to determine its position, locate its celestial targets, track moving targets and remain steadily locked or pointed with very high precision on a specific celestial target.
FGS is so sensitive that it can detect a tiny angular displacement equivalent to the thickness of a human hair as seen from one kilometre away.
NIRISS enables scientists to determine the composition of exoplanets' atmospheres, observe distant galaxies, and examine objects that are very close together.
FGS/NIRISS operates over a wavelength range of 0.6 to 5.0 microns
Fine Guidance Sensor (FGS)
Near Infrared Imager and Slitless Spectrograph (NIRISS)
FGS
The Fine Guidance Sensor (FGS) is a "guider" that "locks on" to bright stars in deep space allowing Webb to point very precisely, so that it can obtain high-quality images.
NIRISS
The Near-Infrared Imager and Slitless Spectrograph (NIRISS) provides near-infrared imaging and spectroscopic capabilities. As the only instrument capable of aperture mask interferometry, NIRISS has the unique ability to capture images of bright objects at a resolution greater than the other imagers. The NIRISS is used to investigate the following science objectives: first light detection, exoplanet detection and characterization, and exoplanet transit spectroscopy.
FGS/NIRISS Instrument Infographic - described in the sections below in the same order as they appear in the graphic.
NASA, ESA, CSA, Andi James (STScI)
Techical Description
The JWST Near-Infrared Imager and Slitless Spectrograph (NIRISS) provides unique observational capabilities between 0.6 and 5 μm that complement those available with NIRCam and NIRSpec. Its efficient, all-reflective design enables low-resolution, wide-field grism spectroscopy; medium-resolution grism spectroscopy optimized for applications  requiring extreme spectrophotometric stability; aperture masking interferometry; and parallel imaging through filters matched to those available with NIRCam.
Components
Camera:
captures two-dimensional images of regions of space.
Spectrograph :
spread light out into a spectrum so that the brightness of each individual wavelength can be measured.
Aperture mask :
a metal plate with seven hexagonal holes that is placed in front of the detectors to increase the effective resolution of the telescope and capture more detailed images of extremely bright objects.
Wavelength
NIRISS is designed to capture light ranging in wavelength from 0.6 microns (visible red) to 5 microns (mid-infrared).
Fields of View
An instrument’s field of view is the amount of sky that it can observe at any given point in time. (The actual area that can be observed depends on the distance of the object being observed.) In this graphic, a Hubble Space Telescope image of the Whirlpool Galaxy (M51) is shown for scale. The image covers an area of 9.6 × 6.6 arcminutes. (The full Moon has a diameter of about 31 arcminutes across the sky.) NIRISS covers a field of view roughly 2.2 × 2.2 arcminutes.
Webb's guider (FGS) and four science instruments (NIRCam, NIRSpec, NIRISS, and MIRI) share the field of view of the Webb telescope optics, but they actually see different parts of the sky at any given observation. Credit: NASA
Imaging Modes
Standard:
is the equivalent to basic digital photography and involves capturing pictures of a wide variety of objects and materials in space that emit or reflect infrared light.
Aperture Mask Interferometry (AMI):
involves using an aperture mask to increase the effective resolution of the telescope and capture more detailed images. When the aperture mask is in place, only the light that passes through the holes makes it to the detectors—the rest is blocked. AMI simulates the effect of a telescope array, in which a number of telescopes work together to simulate the light-gathering ability of a single, much larger telescope. AMI is used to separate light of bright objects like stars that are close together in space or on the sky.
Spectroscopy Modes
Wide-field slitless Spectroscopy:
involves capturing the overall spectrum of a wide field of view: a field of stars, part of a nearby galaxy, or many galaxies at once.
Single-Object Slitless Spectroscopy :
involves capturing the spectrum of a single bright object like a star in a field of view.
FGS/NIRISS Technical Documentation (new tab)
About Webb's Detectors
FGS/NIRISS Development Gallery
Gallery of the development, testing and commissioning of the FGS/NIRISS in reverse chronological order.
The image below is a SLIDESHOW. Hover over the image to see the image title and controls. Click the image to go to a detail page with more info and the ability to download the image at various resolutions (click downward arrow in lower right corner).
View Slideshow as Thumbnail Gallery (new tab)
Video: FGS/NIRISS 3d Diagram Rotation
FGS/NIRISS was built by the Canadian Space Agency.
FGS/NIRISS Development Team
NIRISS is a contribution of the
Canadian Space Agency
to the JWST project.
Honeywell International
designed and built the instrument in collaboration with a team lead by the Principal Investigator,
René Doyon
of the
Université de Montréal
. Additional technical support was provided by the
National Research Council of Canada’s Herzberg Astronomy and Astrophysics Research Centre
The FGS/NIRISS at NASA Goddard before integration into the instrument module.
More on Webb's Instruments
NIRCam
Near Infrared Camera
MIRI
Mid-Infrared Camera
NIRSpec
Near Infrared Spectrometer
FGS/NIRISS
Fine Guidance Sensor / Near Infrared Imager and Slitless Spectrograph
ISIM
Webb's Integrated Instrument Module ( contains all instruments)
Webb Observatory
Observatory Overview Page