Summary/Reader Response draft #3

The article “Why stars look spiky in images from the James Webb Space Telescope'' by Griggs (2022) discussed the causes of distortion in the images produced by the James Webb Space Telescope. These distortions are determined by the telescope being used, and its design and hardware. The JWST is a reflecting telescope that uses light from the universe to form images using mirrors and imaging instruments. The shape of the mirrors affects how lights can diffract around the mirror’s edge. The JWST consists of primary and secondary mirrors, where the primary hexagonal mirrors contribute to the six diffraction spikes in the produced image, and the secondary mirrors are held by three struts that are 25 feet away from the primary mirrors. These struts also contribute to the distortion due to how light diffracts off the struts. There are mainly two instruments that produce images from the telescope. The Near Infrared Camera (NIRCam) uses near infrared lights to capture the image while the Mid - Infrared Instrument (MIRI) uses mid infrared lights. In near-infrared light, the diffraction spikes are prominent as lights at these wavelengths are bright, which enables the stars in images to be more distinct. Images produced by mid infrared lights have lesser distortion, which produces images that are less clear (Webb Space Telescope, 2022).

With the new cameras and mirrors of the JWST, scientists and astronomers are able to have clearer images to study about the history of the universe compared to its predecessor, the Hubble Space Telescope (HST).

The mirrors of the JWST have been improved over its predecessor. The primary mirrors of the JWST 6.5m (NASA, nd-a). It is made out of 18 smaller hexagonal mirrors with a diameter of 1.32m and they are made of beryllium.. They are also coated with layers of highly reflective gold (NASA, nd-a). Weighing about 20Kg, the primary mirrors are both lightweight and strong.. In comparison, the HST’s mirror is about 2.4m in diameter and it is made up of a massive piece of Ultra Low Expansion glass. The glass is coated with “thin layers of aluminium and magnesium fluoride” (NASA,nd-a).  Moreover, Webb’s primary mirror has a light collecting area that is 6.25 times larger than that of HST’s primary mirror. The area is crucial as the JWST was designed to collect lights from longer wavelengths like infrared lights. This is because “light from distant objects is stretched as it travels to Earth” (NASA, nd-a) as they stretch from bright, blue ultraviolet light to dim, red infrared light.

The cameras of the JWST are able to take images at wavelengths that the HST was not able to. The NIRCam is an instrument that captures images of lights at wavelengths 0.6μm to 5μm. It was built by the University of Arizona and Lockheed Martin.(NASA, nd-b), the NIRCam consists of two similar cameras that are mounted back to back. Both cameras can be used simultaneously in survey mode to cover more area for imaging.  The NIRCam is used to detect “the earliest stars and galaxies in the process of formation, the population of stars in nearby galaxies” (NASA, nd-b). It will also capture “young stars in the Milky Way and Kuiper Belt objects.” The MIRI were built between the European Consortium and the Jet Propulsion Laboratory (ESA, nd). It captures images of lights at wavelengths 5μm to 28μm. It is used to study formation of heavy elements, the genesis and evolution of galaxies and old stellar populations. Moreover, it is able to capture images in regions that are blocked by dust (NASA, nd-d). In contrast, the imaging tools in the HST can only take images in wavelengths of 115–1700 nanometers (NASA, nd-c). This will allow astronomers to take clearer pictures as the JWST will be able to take pictures through the space dust which the HST would not be able to.

The downside to the JWST is that it is inaccessible to be serviced. The JWST is located about 1.5million km away from Earth. At the current moment, it is out of reach of any manned vehicles which are being planned by NASA for the next decade (NASA, nd-d). The HST is just 570km away from Earth and it is easily accessible for NASA to service or repair the telescope when needed. However, research and studies have been conducted prior to JWST’s launch to find out if servicing the telescope was worth it or not. These studies came to a conclusion that perks of servicing does not affect the mission intricacy, mass and cost that are needed to make the JWST serviceable (NASA, nd-d).

All in all, JWST is not a new telescope to replace its predecessor. Rather, it is to complement the HST. The potential for the JWST to produce clearer images at higher wavelengths would allow scientists and astronomers to study more about the universe. However, the telescope is currently unserviceable due to it being located so far away from earth that even there are no current plans for NASA to service it.


















References
ESA. (nd). MIRI — the Mid-InfraRed Instrument
https://esawebb.org/about/instruments/miri/


Greene, T., Beichman, C., Gully-Santiago, M., Jaffe, D., Kelly, D., Krist, J., Reiki, M., Smith, E, H. (2011, Jan 1). NIRCam: Development and Testing of the JWST Near-Infrared Camera
https://ntrs.nasa.gov/citations/20110020328


Griggs, M. B. (2022, July 16). Why stars look spiky in images from the James Webb Space Telescope.
https://www.theverge.com/23220109/james-webb-space-telescope-stars-diffraction-spike


NASA. (nd-a). Observatory - Hubble vs. Webb    
https://www.nasa.gov/content/goddard/hubble-vs-webb-on-the-shoulders-of-a-giant


NASA (nd-b). Near Infrared Camera (NIRCam)
https://jwst.nasa.gov/content/observatory/instruments/nircam.html


NASA (nd-c). Hubble Space Telescope stats
https://hubblesite.org/mission-and-telescope/hubble-stats


NASA (nd-d). JWST Frequently Asked Questions
https://jwst.nasa.gov/content/about/faqs/faq.html#serviceable


NASA. (nd). Comparison: Webb vs Hubble Telescope - Webb/NASA
https://www.jwst.nasa.gov/content/about/comparisonWebbVsHubble.html


NASA. (nd). Hubble Space Telescope Observatory - Instruments
https://www.nasa.gov/content/goddard/hubble-space-telescope-science-instruments


Rieke, M. (2020, June 4). JWST advanced deep extragalactic survey: NIRCam imaging to z > 10
https://doi.org/10.1017/S1743921319008950

 Webb Space Telescope. (2021, July 15). Scientific Instruments on the James Webb Space Telescope: Mid-Infrared Instrument (MIRI)
https://webbtelescope.org/contents/media/images/01FA0SZA5HPXKRKH8Y6PKB10V1


Webb Space Telescope. (2022, July 7) Webb’s Diffraction Spikes
https://webbtelescope.org/contents/media/images/01G529MX46J7AFK61GAMSHKSSN
 


















References

ESA. (nd). MIRI — the Mid-InfraRed Instrument

https://esawebb.org/about/instruments/miri/

Greene, T., Beichman, C., Gully-Santiago, M., Jaffe, D., Kelly, D., Krist, J., Reiki, M., Smith, E, H. (2011, Jan 1). NIRCam: Development and Testing of the JWST Near-Infrared Camera

https://ntrs.nasa.gov/citations/20110020328

Griggs, M. B. (2022, July 16). Why stars look spiky in images from the James Webb Space Telescope.

https://www.theverge.com/23220109/james-webb-space-telescope-stars-diffraction-spike

NASA. (nd-a). Observatory - Hubble vs. Webb   

https://www.nasa.gov/content/goddard/hubble-vs-webb-on-the-shoulders-of-a-giant

NASA (nd-b). Near Infrared Camera (NIRCam)

https://jwst.nasa.gov/content/observatory/instruments/nircam.html

NASA (nd-c). Hubble Space Telescope stats

https://hubblesite.org/mission-and-telescope/hubble-stats

NASA (nd-d). JWST Frequently Asked Questions

https://jwst.nasa.gov/content/about/faqs/faq.html#serviceable

NASA. (nd). Comparison: Webb vs Hubble Telescope - Webb/NASA

https://www.jwst.nasa.gov/content/about/comparisonWebbVsHubble.html

NASA. (nd). Hubble Space Telescope Observatory - Instruments

https://www.nasa.gov/content/goddard/hubble-space-telescope-science-instruments

Rieke, M. (2020, June 4). JWST advanced deep extragalactic survey: NIRCam imaging to z > 10

https://doi.org/10.1017/S1743921319008950

 Webb Space Telescope. (2021, July 15). Scientific Instruments on the James Webb Space Telescope: Mid-Infrared Instrument (MIRI)

https://webbtelescope.org/contents/media/images/01FA0SZA5HPXKRKH8Y6PKB10V1

Webb Space Telescope. (2022, July 7) Webb’s Diffraction Spikes

https://webbtelescope.org/contents/media/images/01G529MX46J7AFK61GAMSHKSSN

 




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