Editing 2906: Earth

{{comic
| number    = 2906
| date      = March 13, 2024
| title     = Earth
| image     = earth_2x.png
| imagesize = 364x472px
| noexpand  = true
| titletext = Just think of all the countless petty squabbles and misunderstandings, of all the fervent hatreds, over so insignificant a thing as the direction and duration of a rocket engine firing.
}}

==Explanation==
[[File:Pale Blue Dot.png|200px|right|thumb|The ''Pale Blue Dot'' image from Voyager 1. Earth is the "pale blue dot" halfway up the rightmost color band.]]
At first sight, this appears to be the famous {{w|Carl Sagan}} commentary, upon the ''{{w|Pale Blue Dot}}'' image of Earth, a picture taken by the {{w|Voyager 1 probe}} in 1990 (at that time 6 billion kilometers away) but having been transmitted back to Earth to be appreciated as one of the most iconic 'photos of Earth from space', along with ''{{w|Earthrise}}'' and ''{{w|The Blue Marble}}''. Sagan's written, and later spoken, words evoke how the lives of all of us are somehow confined to barely more than a single pixel's-worth of existence upon an already zoomed-in view of space.

From the caption, however, it appears that 'Carl' is not looking at an image. Instead it is a spacecraft window. The minute apparent size of the Earth is as a result of the spacecraft being very far from Earth. This is an unintended consequence of an attempt to deorbit from {{w|low Earth orbit}} (i.e. not more than 2000 kilometers from the Earth's surface, from which the Earth should still mostly fill any view that points towards it). Rather than transitioning from LEO into a re-entry trajectory, somehow the vessel and crew have been sent into a ''much'' higher-reaching orbit, if not into a solar or extra-solar trajectory. And it is apparently Carl's fault. The speech is thus not an inward view of where we all are, but an outward look at somewhere that all the crew (unwillingly, and against all recent expectations) are ''not''.

<!-- NOT SURE IF THIS NEW PARAGRAPH IS NEEDED. "BLUE MARBLE" ALREADY MENTIONED (AS SEPARATE), AND WE ALREADY HAVE REFERENCED CORE INFLUENCES AND MORE. THOUGH MAYBE SOMEONE CAN RE-USE/RE-EDIT SOME OF IT? -- This comic is not (although it appears as to the uneducated pre-astronomer who watches [https://en.wikipedia.org/wiki/Jay_Foreman_(comedian) map men]) a reference to the [https://en.wikipedia.org/wiki/The_Blue_Marble Blue Marble] image taken on the moon. The most common distribution of this image has been cropped to remove most of the empty space, and rotated so [https://www.youtube.com/watch?v=B14Gtm2Z_70 north was up]. -->
The title text continues with the traditional tone of the speech, only to become an implicit attempt to claim that it wasn't quite as drastic an error as it actually seems to have been.

The very same words (or as far as they go), but in the more traditional situation of an informative lecture, were previously used in [[1246: Pale Blue Dot]].

=== The scale of the error ===

The comic's distance from Earth is unlikely to be anywhere near that of Voyager 1, and would not be being seen portrayed by the same 1500mm high-resolution narrow-angle camera as took the alluded-to image. The apparent size of Earth, compared with Carl at his window, would depend a lot on the actual 'camera' geometry/position for the scene. For comparison, however, the Earth seen from the Moon is slightly under four times the diameter of the Moon as seen from the Earth, or perhaps nearly the size of a clenched fist, held at arm's length. This implies (unless the scene uses a particularly wide-angled lens, close to Carl and the window) that the vessel's position is now ''significantly'' beyond the orbit of the Moon.

The ''absence'' of a clearly visible Moon, which would have a near-identical phase to the illuminated Earth and could easily be the second brightest object in the scene, is therefore best explained by it being no more than a sub-pixel object, indistinguishable from the surrounding darkness of space, somewhere within thirty Earth diameters (and thus [[2205: Types of Approximation|approximately]], in this image, pixels) of the visible Earth. This could include being sufficiently in conjunction/opposition to Earth to blend in, or be obscured by it.<!-- Note just for those who pass by this source: This excludes the 'out there' humorous possibility that the badly-done manouver did not effect the spacecraft, so much as it somehow sent the *Earth* out of its position, leaving the ship (and the Moon, and more than half of all other satellites?) still technically continuing more or less their prior Earth-orbits - which are now technically various solar ones... (BunsenH:)This could be a remake of {{w|Space: 1999}}. (OP:)Indeed, but actually turned up several notches! -->

The general lack of other visible stars, etc, would be explained by the exposure being tuned to not wash out the illuminated internal view, and not being set up for useful astronomical shots, though may then set another range of useful limits on what magnitude of reflected sunlight must still arrive from Earth in order to remain visible.<!-- Additional bonus note: This would depend upon the effective Earth-phase, Earth-albedo (e.g. ocean/land/ice-cap as prime reflector), the actual levels of the running lights by the 'cupula' viewing window and possible lower-dynamic-range capabilities/adjustments to the resulting image by the hypothetical 'comic camera', perhaps other details. On top of it being more governed by Rule Of Funny than *strict* reality, I suggest that making the actual calculation would be more troublesome than it's worth. Right? -->

The orbital speed in low-earth orbit is ~8km/s. Escape speed is ~11km/s. So to reentry the spacecraft must do a retrograde burn of some hundreds m/s, while to escape it must do a prograde burn of ~3km/s. So it must have been quite an error (~10 times bigger and in the opposite direction).

=== The "pale blue" dot ===
Although it might initially look like a white dot, the comic truly has used a pale blue color for the dot that represents Earth, with the color used in the "2x" version of the image seeming to be 0xBDCFF4.

This can be interpreted as predominently a very light gray, with an extra hint of green and a bigger hint of blue. Or redefined as an {{w|HSL and HSV|HSV}} triplet of of 220.4 (a greenish-blue hue), 22.5% (relatively unsaturated) and 95.7% (very bright), all consistent with how the sunlit side of an Earthlike world would look with large oceans, vast swathes of terrestrial vegetation and atmospheric clouds, necessarily abstracted down to a very limited number of pixels.

Looking at {{w|File:Pale_Blue_Dot.png|an actual example of the 'original'}}, seems to give a possible RGB of 0x95B39E (which gives: hue of 138, i.e. a 'bluish-green'; saturation level of 16.8%; brightness value of 70.2%), which is of course also consistent with the above assumptions about Earth. But all such images are of course ultimately derived as a composite of the data from [https://pds-rings.seti.org/voyager/iss/inst_cat_na1.html#filters eight separate 'filters'], which don't neatly fit into the {{w|RGB color model}}, and always subject to various kinds of post-processing and image conversion techniques.<!-- Maybe someone can find an actual 'original original' from NASA/JPL/whoever, or even the original eight 'raws'..? -->

==Transcript==
:[Carl Sagan (drawn Cueball like but with flat hair) is standing in front of a black screen with a tiny pale blue dot in the middle. He indicates the screen by holding out his right hand palm up towards the screen. He is speaking to someone off-panel, who replies from a star burst on the right edge of the panel.]
:Carl: Look again at that dot. That's home. On it everyone you love, everyone you know, everyone you ever heard of, every human being who ever was, lived out their lives...
:Carl: On a mote of dust suspended in a sunbeam.
:Off-panel voice: We '''''know,''''' Carl.

:[Caption below the panel:]
:Carl Sagan was '''''not''''' making us feel better about how badly he'd messed up the low Earth orbit reentry burn.

{{comic discussion}}

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