Editing 2564: Sunshield

{{comic
| number    = 2564
| date      = January 5, 2022
| title     = Sunshield
| image     = sunshield.png
| titletext = RIP the surface of Mars
}}

==Explanation==
This is another comic with a [[:Category:Facts|Fact]], though not a [[:Category:Fun fact|Fun fact]] - this time an Astronomy fact. The next comic with a fact, namely [[2596: Galaxies]], was also with an Astronomy fact. This is the first time that the field that a fact pertains to has been immediately repeated.

JWST stands for {{w|James Webb Space Telescope}}, a space telescope that was launched 12 days prior to publication of this comic, see more details here [[2559: December 25th Launch]]. 

It has a {{w|James Webb Space Telescope sunshield|sunshield}} to protect its instruments from the heat of the sun and to keep them below 40 K (-233 °C/-388 °F). Deployment of the sunshield was completed the day before the comic was published. The JWST has to undergo a complex sequence of deployment steps to unfold parts that had to be packed tightly for launch. This sequence has 344 possible points of failure that would render the very expensive space telescope useless; 75% of them led up to the successful full deployment of the sunshield. Thus successful steps are widely celebrated, with this comic an example of such a celebration.

Ordinary cameras use a {{w|Flash (photography)|flash}} to take pictures in low-light situations. Outer space is very dark {{Citation needed}} (one of the JWST's mission objectives will help astronomers calculate exactly [https://www.nasa.gov/feature/new-horizons-spacecraft-answers-question-how-dark-is-space how dark]), so this comic posits that the JWST has a very powerful flash to compensate for this. Most astronomical cameras don't use flash photography {{Citation needed}} -- they depend on the light either emitted by objects themselves (e.g., stars) or from nearby very bright objects (e.g., Solar System planets will reflect the Sun's light, while distant clouds of gas and dust may be largely illuminated by the light of supernovae or recently formed stars within or near them). A flash generally doesn't work for many reasons:
* It would take too long for the light of the flash to return to the telescope - at least twice the time that it had already taken for the original image to arrive on its own.
* The clicking sound indicates that the JWST is using a camera with mechanical parts that are moving in order to take a picture. This can be a mirror of a single lens camera, where the clicking noise is produced by the mirror moving away to allow the light to reach the sensor. Alternatively the shutter in front of the sensor produces a clicking noise when it is opening to start the exposure. In the latter case the opening of the shutter would happen ''before'' the flash is emitted, so light from the flash wouldn't even reach the camera's {{w|image sensor}}. It is however possible that the camera is using a time exposure and that the shutter was still open when the flash occurred.
* Not enough 'flash' light would return due to it uselessly spreading in all directions. Instead, in a telescope mirrors and/or lenses focus the light, and long exposure times are used to collect enough of the current light to form a decent image.
* A flash powerful enough to overcome the previous difficulty would have to be inordinately powerful. This would raise significant questions about powering it, its destructive effect on JWST, and its damage to (or at least disturbance of) many of the things the flash would be able to illuminate.
* The objects and phenomena of interest of JWST are, by dint of their extreme distance, being seen as they were in the early stages of the universe, and emit light that potentially gives vital clues about that era, only marginally this side of the current visible-horizon of our apparently expanding universe. Should our flash ever reach them (assuming they still exist) and we have the patience to await the return (assuming ''we'' still exist), this will only reveal the much older versions of whatever they have become and only in the form of light that we have swamped them with.
* Before this, any intervening civilization that possesses (or can still develop) the necessary capabilities will have at the very least responded, if not retaliated, to the original flash. Their response might be far less humorous.

There are some examples of astronomical research done using things similar to a flash. {{w|Radar astronomy}} involves emitting radio waves (microwaves) that bounce off distant planets, asteroids, comets, etc., and analyzing the returned waves. The {{w|Lunar Laser Ranging experiment}} uses lasers, which are loosely related to flashes for photography, to measure the distance between Earth and Moon. The outward light is concentrated upon the approximate area of the lunar target, which employs an {{w|Retroreflector|optical trick}} to send most of that which actually struck it back to the approximate area of the source equipment.

The comic assigns the sunshield a new, comical purpose of shielding the Sun (and Earth ,which is roughly in the same direction as the Sun, due to the deployment at the {{w|Lagrange point|L2 Lagrange point}}) from this flash, rather than the other way around. When the camera is taking a picture, the comic shows space in front of the shield lit up while there is a totally dark shadow behind the shield (in the direction of Earth and Sun).

The comic also has the camera making a "click" sound. In traditional mechanical cameras without a mirror, this sound comes from the {{w|Shutter (photography|shutter}} opening and closing, and mirror-less digital cameras mimic this sound so the user (and subject, when human) knows when the picture is being taken. JWST won't actually click -- it doesn't have a shutter, as it takes long-exposure digital images, and [https://www.imdb.com/title/tt0078748/taglines in space no one can hear you click].

The telescope also tells the universe to smile for the picture. The universe doesn't have a mouth to smile with{{Citation needed}}, although there are a number of features both on Solar System objects and in deep space that look like faces; this is a phenomenon called {{w|pareidolia}}. The most well known is the {{w|Man in the Moon}}, but there are numerous others both in the [https://www.universetoday.com/121551/faces-of-the-solar-system/ Solar system], most famous is probably the {{w|Cydonia (Mars)|Face on Mars}} and out among the galaxies, like the [https://apod.nasa.gov/apod/ap151127.html Cheshire Cat galaxy group] named after the {{w|Cheshire_Cat#In_science|Cheshire Cat}} from {{w|Alice's Adventures in Wonderland|Alice in Wonderland}}.

The title text suggests that, due to the sunshield not being angled to shield Mars, Mars's surface has been badly scarred by the flash. This implies ''incredible'' strength of the flash, perhaps to ensure the light can return from its destinations, comparable to {{tvtropes|KillSat|death-ray satellites}} in fiction.

There is an interesting parallel to [[1378:_Turbine|xkcd #1378 ("Turbine")]] in which the wind turbine must correct Megan by explaining that it is "not a huge fan".  The turbine is meant to absorb energy from wind, not propel it outwards; the same goes for JWST and light in 2564.

==Transcript==
:[The James Webb Space Telescope (JWST) is floating through space, shown in white on a pitch black background. The two mirrors are seen in front of the sunshield, which is kite shaped. A white line goes from the telescope up to two lines of white text, connected with a small white line.]
:JWST: Okay, universe-
:JWST: Smile!

:[Same setting, but now only a small thin white line goes up to a line of white text representing a sound made by the telescope.]
:JWST: ''Click''

:[Same setting, but now it turns out that a small bulb on the front of the telescope is a flash light. A bright flash glows from the bulb, turning most of the panel white. A cone on the left side is blocked and kept pitch black by the telescope's sunshield. The light fades a bit towards the edges of the picture, giving the light cone a rounded appearance. Thus the image actually looks a lot like Pac-Man in the process of eating the telescope.]

:[Caption below the panel:]
:Astronomy fact: The purpose of the JWST sunshield is to protect the Sun and the Earth from the telescope's powerful flash.

{{comic discussion}}

[[Category:Comics with inverted brightness]]
[[Category:Facts]]
[[Category:Telescopes]]
[[Category:Astronomy]]
[[Category:Photography]]