Monday, July 25, 2011

The NIRCam Instrument

The NIRcam (Near Infrared Camera)
The James Webb Space Telescope has a number of scientific instruments and features that will help us to understand just what is going on out here in the Universe. First and foremost is the telescope - 18 gold-coated beryllium hexagonal mirrors, secondary mirrors, and other support structures that will comprise one of the most advanced optical machines ever built. Additionally, there is the ISIM and the Sunshield. The ISIM (Integrated Science Instrument Module) contains 4 scientific instruments. They are as follows:
  • NIRCam - The Near Infrared Camera
  • NIRSpec - The Near Infrared Spectrometer
  • MIRI - The Mid-Infrared Instrument
  • FGS-TFI - The Field Guidance Sensor Tunable Filter Camera
The NIRCam - the Near Infrared Camera - is one of the more important tools on the JWST. As the name implies, it will see in the Near Infrared portion of the spectrum.

What is Infrared Light? 

Generally, the infrared area of the electromagnetic spectrum (see left) is the area that covers the wavelength range from roughly 300 GHz (1 milimeter) to 400 THz (750 nanometers). It can be divided into three sub-regions:

  • Far-Infrared
  • Mid-Infrared
  • Near-Infrared
The wavelength of the infrared portion of the EM (EM = Electromagnetic) Spectrum is longer than that of visible light. Our eyes, evolved over hundreds of millions of years, never tuned into IR wavelenghts (IR = Infrared). Therefore, we cannot see IR without the aid of specially designed lenses and instruments that can block the visible light that we normally see. 

However, just because you don't see it doesn't mean it isn't there. Infrared is usually part of most of the light that we see. The sun emits IR light along with the bright sunshine that blankets the Earth. As a result of constant light from the sun, many objects, plants and animals on the Earth will reflect IR light the same as light from the visible part of the EM spectrum. 

Bats emitting heat, as seen in IR
Importantly, IR light is given off when heat of a specific range of temperatures is reached. Since light is a form of radiation (energy radiating away from a source), atomic materials in the course of their normal atomic functions give off energy, which radiates out and can be seen somewhere on the EM Spectrum. IR light is specific to a certain range of energy or heat. Anything that is within a specific range of temperature will give off Infrared light in addition to other kinds of electromagnetic radiation (see right). 

Using Infrared Spectrum to Understand

Now that humanity understands what gives off IR light/radiation, we can use it to understand more about the world around us and to improve the technology we use. We use IR spectrum analysis to aim military drones at targets, to provide insight and details about a weather forecast, studying the efficiency of cell phone communication, night vision, television remotes, communication among computer devices, etc, etc...

Timeline of the Universe. Click to embiggen. 
Most telling for the JWST is that infrared can be used to greatly increase our understanding of the universe. Lots of things in the Universe happen all across the Electromagnetic Spectrum, including the Infrared. Importantly, lots of things DID happen in the Infrared, too, way back in the distant past of our 13 billion year old Universe. Much of the light from the early universe is coming to us still...even right now, at this moment. Our universe is SO OLD and SO MIND-POPPINGLY HUGE that light from the beginning of time is still traveling across the vastness of space and spilling across our Earth. When you look up into the sky, you are truly looking back in time. 

Simulation of JWST View
Since we can observe that the Universe is expanding (thanks in part to the Doppler Effect), anything moving away from us will emit light in the red end of the spectrum. Although Hubble helped us to understand that the expansion of the Universe is actually accelerating, the James Webb Space Telescope NIRcam will be the instrument that can see the details of that cosmological redshift. From the JWST Wikipedia entry: 

Looking beyond our own galaxy to more distant galaxy clusters, quasars, and gamma-ray bursts, the most distant objects viewable are also the "youngest," that is, they were formed during a time period closer in time to that of the Big Bang. We see them today because their light has taken billions of years to reach us. Because the universe is expanding, as the light travels it becomes red-shifted and are therefore easier to see if viewed in the infrared. JWST's infrared capabilities are expected to let it see all the way to the very first galaxies forming just a few hundred million years after the big bang.

The NIRCam

The Near Infrared Camera will focus on a particular area of the Infrared portion of the Electromagnetic Spectrum. It will be able to see right through cloudy nebulae and pick up many details in the night sky that Hubble and Spitzer cannot see. It will be this instrument aboard JWST that makes the difference.

NIRCam will fit inside the larger ISIM assembly/structure. It will reflect light through a series of implements that will eventually process the incoming image. Here is an image from the University of Arizona website (UA built the NIRCam) coupled with an explanation of the pathway the light will take provided by the Space Telescope Science Institute website (STSI will be running the NIRCam):

Click to Embiggen
The incoming light initially reflects off the pick-off mirror. Subsequently it passes through the collimator and the dichroic, which is used to split the light into the short (0.6-2.3µm) and long (2.4-5.0µm) wavelength light paths. Each of these two beams then passes through a pupil wheel and filter wheel combination, each beam having its own separate pupil and filter wheel. After this, the light passes through the camera corrector optics and is imaged (after reflecting off a fold flat in the short wavelength beam) onto the focal plane arrays (FPAs).

The NIRCam will be able to perform several basic operations. Those include:

  • two types of imaging (small source imaging and survey imaging)
  • coronagraphy (blocking out the main source of light to study the corona) 
  • spectroscopy (studying the composition of something through the light they reflect/give off) 
  • wavefront sensing (useful in aligning the primary mirrors. This is important for the life of the telescope and the quality of images received/produced...therefore this feature has some redundancies)
The NIRCam is also outfitted with Grisms (think prisms but with gratings so that only certain wavelengths of light can enter). With Grisms, "one and the same camera can be used both for imaging (without the grism) and spectroscopy (with the grism) without having to be moved" (wikipedia entry). Having the ability to perform spectroscopy in this way will make the JWST "especially useful for high precision spectrophotometric observations of transiting exoplanets" (from Observing Exoplanets with the JWST NIRCam Grisms). The JWST will not only study the general birth of the Universe, but look for and help study the birth of life. 

As of June 2011, the ISIM (which contains the NIRCam and the other science instruments) is 90% complete on manufacturing, with NASA contractors planning on ISIM instrument integration soon. 

More information on the NIRCam can be found at the following links: 

As always Science Warriors, it only takes 4 steps to save the JWST: 

 a) Sign the Petition
   b) Like the Facebook Page
   d) Spread the Word



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