Summary/Reader Response Draft #1

From the webpage “Why stars look spiky in images from the James Webb Space Telescope” from The Verge (2022) tells us the reason why the stars look spiky. The features from the James Webb Space Telescope (JWST) contribute to why the star looks spiky in images from JWST. The mirror on the space telescope, the near-infrared cameras (NIRCam) and sunshields Observatory the Webb Observatory, n.d). The shape of the primary will affect how the light is reflected onto the secondary mirror. Hence, a hexagonal mirror results in an image with six diffraction spikes from The Verge (2022). The near-infrared camera (NIRCam) is JWST’s primary imager capable of covering a “wavelength range 0.6 to 5 microns” (Instrument NIRCam, n.d). NIRCam can detect light from the earliest stars and galaxies in the process of formation. The near-infrared spectrographs (NIRSpec) is an instrument that analysis the wavelength that is captured by the NIRCam (Instrument NIRCam, n.d). JWST has a 5-layer, tennis court-size sunshield that acts like a parasol providing shade (Observatory the Sunshield, n.d). With the function of the NIRCam, JWST is not a replacement but a successor to Hubble Space Telescope.

One enhanced feature of the JWST is the size and shape of the primary mirrors. According to Erickson (2022), the telescope can see more detail the larger the mirror. A huge, weighty mirror is incredibly challenging to send into space. Engineers, therefore, provided the telescope with 19 smaller mirrors that interlock like a puzzle. The mirrors are folded within the rocket, then they are unfurled to create a single huge mirror in orbit. Around surfaces like mirror edges, light diffracts or beds. As light interacts with the mirror's edges, it can be the shape of the mirror itself that causes these light spikes (Griggs, 2022). A nearly round, segmented mirror with a "high filling factor and six-fold symmetry" is made possible by the hexagonal shape. A high filling factor indicates that there are no gaps between the segments. The segments would have gaps between them if they were circular (Observatory Webb’s Mirror, n.d). Hubble Space Telescope, in contrast, “the mirror was round, so it didn’t add to the spikiness” (Griggs, 2022). Gianopoulos (2021) states that Webb’s 21.3-foot (6.5-meter) primary mirror is substantially bigger than Hubble's 7.9-foot (2.4-meter) primary mirror, providing Webb with a light-collection surface that is more than six times that of Hubble.

Another feature of the JWST that shows JWST is not a replacement but a successor is the near-infrared camera (NIRCam). According to WebbTelescope (2021), one of the four scientific tools onboard the Webb spacecraft is the Near-Infrared Camera (NIRCam). The main near-infrared imager aboard Webb, NIRCam, offers high-resolution imaging and spectroscopy for a variety of research projects. NIRCam is essential for many planetary research since it is the only near-infrared instrument with coronagraphic and time-series imaging capabilities. NIRCam is a component of Webb’s wavefront sensing and control system, which in addition to imaging and spectroscopy also detects and corrects for minute imperfections in the primary mirror’s shape and misalignment between mirror segments, enabling the telescope to focus clearly on both nearby and distant objects. In contrast, Hubble Space Telescope has two primary camera systems the Advanced Camera for survey (ACS) and the Wide Field Camera 3 (WFC3) to capture the cosmos. Garner (2017) states that ACS was primarily made to survey enormous “areas of the sky at a visible and red wavelength with times” more efficient compared to the previous top Hubble camera, the Wide Field Planetary Camera 2 (WFPC2). Garner (2017) states that WFC3 investigates a wide variety of objects and processes, including exoplanets, young, very distant galaxies, much closer stellar systems and items in our own solar system. Its capacity to cover the entire electromagnetic spectrum, from ultraviolet (UV) to visible, is its important characteristic from light to the near-infrared (NIR). In addition to allowing Hubble to view father into the cosmos, WFC3 also allows for the provision of images in the UV, visible and near-infrared (NIR) spectrums.

The last feature of the JWST is the sunshield. Observatory the sunshield (n.d) states that the infrared light emitted by dim and extremely far-off objects will be predominantly seen by the JWST. The telescope itself must be maintained at a very low temperature in order to be able to detect those little heat signals. Webb includes a 5-layer, tennis court-size sunshield that acts like a parasol to provide shade in order to shield the telescope from heat and light coming from the observatory itself as well as from other sources (such as the Sun, Earth, and Moon). According to NASA (n.d), by passively releasing its heat into space, the sunshield will enable the telescope to drop to a temperature below 50 Kelvin (-370°F or -223°C). Through a passive cooling system, the near-infrared instruments (NIRCam, NIRSpec, FGS/NIRISS) will operate at roughly 39 K (-389°F, -234°C). The working temperature for the mid-infrared instrument (MIRI) is 7 K (-447°F, -266°C).

One advantage the Hubble Space Telescope has over the James Webb Space Telescope will be the orbital distance to earth. Hubble Space Telescope is orbiting at low earth orbit whereas JWST is orbiting between Earth-Sun L2 Lagrange point. According to Webb vs Hubble Telescope (n.d.) the Hubble Space Telescope “orbits around the Earth at an altitude of~570 km above it”. Instead of orbiting the Earth, Webb will be 1.5 million kilometers distant at the L2 Lagrange point. Orbiting at around 570 km from earth, it allows NASA to conduct service missions to maintain or install new instruments for Hubble Space Telescope. Hubble was built to support routine maintenance and equipment updates while in orbit. As replacement units for orbital debris, instruments and limited-life things were created. NASA Space Shuttle carried out five service missions (SM 1, 2, 3A, 3B and 4), the first in December 1993 and the last in May 2009 (“Hubble Space Telescope,” 2022).

In conclusion, although Webb is frequently referred to as Hubble's replacement, we prefer to use the term "successor." Since Webb is the scientific successor to Hubble, the results of Hubble served as the basis for its scientific objectives. The science behind Hubble compelled us to "go beyond" what Hubble has previously accomplished by turning to longer wavelengths. Particularly, farther away objects are more strongly redshifted, pushing their light out of the UV and optical spectrum and into the near-infrared. An infrared telescope is thus necessary for views of these far-off objects, such as the first galaxies that the universe's beginnings produced (About Webb vs Hubble Telescope, n.d.).

 

 

References

About Webb vs Hubble Telescope. (n.d.). James Webb Space Telescope. https://www.jwst.nasa.gov/content/about/comparisonWebbVsHubble.html

Observatory the Sunshield. (n.d.). James Webb Space Telescope. https://webb.nasa.gov/content/observatory/sunshield.html

Observatory the Webb Observatory. (n.d.). James Webb Space Telescope. https://webb.nasa.gov/content/observatory/index.html

Observatory Webb’s Mirror. (n.d.). James Webb Space Telescope. https://webb.nasa.gov/content/observatory/ote/mirrors/index.html

Erickson, K. (2022, September 26). What is the James Webb Space Telescope? Space Place https://spaceplace.nasa.gov/james-webb-space-telescope/en/ 

Garner, R. (2017, December 5). Observatory - instruments. NASA. https://www.nasa.gov/content/goddard/hubble-space-telescope-science-instruments

Gianopoulos, A. (2021, December 13). Observatory - Hubble vs. Webb. NASA. https://www.nasa.gov/content/goddard/hubble-vs-webb-on-the-shoulders-of-a-giant

Griggs, M. B. (2022, July 15). Why stars look spiky in images from the James Webb Space Telescope. The Verge. https://www.theverge.com/23220109/james-webb-space-telescope-stars-diffraction-spike

Hubble Space Telescope. (2022, September 7). In Wikipedia. https://en.wikipedia.org/wiki/Hubble_Space_Telescope#Servicing_overview

Instrument: NIRCam. (n.d.). James Webb Space Telescope. https://webb.nasa.gov/content/observatory/instruments/nircam.html

Instrument: MIRI. (n.d.). James Webb Space Telescope. https://webb.nasa.gov/content/observatory/instruments/miri.html

MIRI factsheet (n.d.). The European Space Agency. https://www.esa.int/Science_Exploration/Space_Science/MIRI_factsheet

Scientific instruments on the James Webb Space Telescope: Near-Infrared Camera (NIRCam). (2021, July 15). Webb Space Telescope. https://webbtelescope.org/contents/media/images/01FA0SZSEW1TZ51BHG0EGW2EZP

Webb vs Hubble Telescope. (n.d.). James Webb Space Telescope. https://www.jwst.nasa.gov/content/about/comparisonWebbVsHubble.html#orbit