2849: Under the Stars

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Under the Stars

Title text: If you live in Los Angeles (around 33°52'N, roughly the latitude of Hermosa Beach) the black hole in V404 Cygni passes over you each day. On Christmas Day it will be directly overhead around 2pm.

Explanation

The phrase "under the stars" generally refers to being under a visible field of stars (either real stars visible at night, or representations of stars constructed by people, as in a dance hall). Megan points out that we're always under the stars, they're just obscured ("painted over") during the day by the brightness of the Sun and its interaction with the sky. Of course, this makes the 'under the stars' part of the remark redundant in the first place, because by this definition, sitting outside is always under the stars. Also, since the Sun is itself a star, regardless of whether the other stars exist when it's daytime or not, you would always be under at least a star. In fact, sitting inside is arguably under the stars as well, since the stars are still there, but just obscured by a roof or other construction. Poetically, though, it could be taken to mean that Megan simply loves to sit and ponder the very existence, vastness, etc. of the stars, even when she can't see them.

If you live on the blue line, the black hole in V404 Cygni is directly over you once a day. Zoomable version here.

This is related to the concept of object permanence, which is the understanding that objects continue to exist even though we can't physically sense them. When you close your eyes, the universe doesn't go away even though you can't see it; similarly, when the Sun is shining, the stars are still all there.

In the early days of xkcd, it was common for Randall to publish a comic that was not intentionally funny -- often also featuring Cueball and Megan -- so this is a bit of a return to form.

The title text mentions V404 Cygni, a binary system composed of a 9 solar masses black hole and a star smaller than the Sun. With a declination of +33° 52′ 02.0″, once every 23 hours and 56 minutes (366.24 times per year, compared to 365.24 solar days within the same timeframe), it 'passes over' any point of the rotating Earth with that latitude North, like Los Angeles, Atlanta or Beirut.

The night sky being "terrifying" is probably related to a quote from Blaise Pascal:

“I see the terrifying spaces of the universe that enclose me, and I find myself attached to a corner of this vast expanse, without knowing why I am more in this place than in another, nor why this little time that is given me to live is assigned me at this point more than another out of all the eternity that has preceded me and out of all that will follow me.” [1]

This may also be a subtle reference to the novel Nightfall by Isaac Asimov and Robert Silverberg which takes place on a planet that has so many suns they never have darkness and can never see the stars. In that novel there is an eclipse which occurs roughly every 2050 years, which causes a complete psychological breakdown of everyone on the planet, as they all fear the dark and have no concept of the vastness of space. In this comic the reference to every sky being full of stars being "terrifying" is very reminiscent of that novel (which was probably referring to Pascal's quote).

Transcript

This transcript is incomplete. Please help editing it! Thanks.

[Megan and Cueball are sitting in a field under a clear blue sky and bright Sun.]

Megan: I love sitting out under the stars.

Cueball: ...It's daytime.

Megan: Yeah, but the stars are all still up there.

Megan: Constellations wheel overhead; they're just painted over with blue.

Megan: Every sky is full of stars.

Cueball: That's somehow terrifying.

Megan: It's okay—just look at that sunny sky and tell yourself space isn't real.

Megan: "Daytime" is us closing our eyes and pretending it makes infinity go away.

Trivia

• The sun and grass are continuously drawn between frames, as if the frames are organized spatially instead of temporally.
• The idea of considering what celestial objects are directly above a given location has been visited before in the Star Ownership What if?

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Discussion

Reminds me a lot of many of Randall's first few dozen XKCD's that weren't trying to be funny but just kind of sweet and observational. Laser813 (talk) 15:32, 1 November 2023 (UTC)

"Mostly void, partially stars..." 172.71.151.161 18:07, 1 November 2023 (UTC)

Is the title text trying to relate the black hole to the Star of Bethlehem? Barmar (talk) 15:49, 1 November 2023 (UTC)

No, he's just trying to make you freak out that a black hole is RIGHT ABOVE YOUR HEAD!!! ;) Elektrizikekswerk (talk) 16:31, 1 November 2023 (UTC)

Good thing I don't live in Los Angeles :) Me^{[citation needed]} 16:54, 1 November 2023 (UTC)

On the other hand, I live pretty damn near Atlanta, so it's pretty damn close to coming over my head every day... Edit: Just checked the zoomable map... it goes right over my head every day someone, i guess^{(talk i guess|le edit list)} 17:44, 1 November 2023 (UTC)

Well, I'm 20ish° away from that track (and have never actually been anywhere near that latitude, despite occasional intercontinental travel). Looks like I'm not going to be in danger of hitting a black hole.... 172.70.90.220 18:48, 1 November 2023 (UTC)

I think we need a category for "comics in full color" since there are 519 with color, but most of those aren't full color Laser813 (talk) 18:25, 1 November 2023 (UTC)

Technically, it's not in full color, because Cueball and Megan's heads are white, not skin tone someone, i guess^{(talk i guess|le edit list)} 18:48, 1 November 2023 (UTC)

As I was thinking. But I was trying to think of a good word (like "photorealistic", though it isn't quite that) to describe significant arty/colourwashed scenic elements. There are a handful of comics (I think, without trawling through the candidates I have in mind, or look for others) that are so coloured. 172.69.194.194 19:03, 1 November 2023 (UTC)

Maybe that is their skin tone, though. skin colours in comic strip land don't necessarily correspond to those in human experience land. 172.71.242.140 09:12, 2 November 2023 (UTC)

Is there something significant about V404-Cygni? Surely there are enough black holes that there's at least one that passes over every line of latitude. Barmar (talk) 19:31, 1 November 2023 (UTC)

My best guess: Randall picked it at random because it's funny. someone, i guess^{(talk i guess|le edit list)} 23:31, 1 November 2023 (UTC)

I'm thinking he chose it because of its number – V404.  Isn't '404' the internet error code for something that can't be found... something that has figuratively slipped into a black hole somewhere? RAGBRAIvet (talk) 07:29, 2 November 2023 (UTC)

As I recall, he previously quoted this particular black hole in a prior "passes directly over..." reference, which perhaps (I can't quite remember how, without searching) tied in with the requirements of that particular comic/article/whatif. And, at some point, you're gonna get yourself a 'favourite' that you'll reference whenever you get a decent chance, right? 172.70.85.28 08:45, 2 November 2023 (UTC)

Unfortunately not. What If? 161 mentions Cygnus X-1, but no mention of V404-Cygni someone, i guess^{(talk i guess|le edit list)} 00:59, 3 November 2023 (UTC)

To quote wikipedia: In 2009, the black hole in the V404 Cygni system became the first black hole to have an accurate parallax measurement for its distance from the Solar System. -- Hkmosealy (talk) 00:10, 2 November 2023 (UTC)

The Earth wobbles quite a bit. How long will it be pointing close enough (I guess within 1 minute of declination) that V404-Cygni will be over that specific line of latitude? Nitpicking (talk) 02:30, 2 November 2023 (UTC)

If I'm reading [2] correctly only 72 years, but that seems surprisingly short to me. Perhaps I am missing a conversion factor? 172.69.34.49 23:25, 2 November 2023 (UTC)

The title text reminds me of what if? 161 MrCandela (talk)

You're thinking of Cygnus X-1, a similarly named and located but completely 0different black hole. Cygnus X-1 and V404-Cygni appear to be unrelated to each other, besides being within Cygnus someone, i guess^{(talk i guess|le edit list)} 00:53, 3 November 2023 (UTC)

Out today just before noon (local time, but of course it doesn't matter much which local time) I saw in the significantly bright blue sky... a partially built planet-destroying space-station the Moon. Which of course you do. But reminds me of the time when just such a prominent daytime phased-Moon was visible when children were being let out from school and there was this conversation with a supervising member of staff (I forget why, might even have been from "today we learnt about the skies/time!" from the child involved) where we pointed out the Moon up in the bright blue sky and he refused to look!. Not sure if he suspected a practical joke, "didn't want to confuse his pupils" or genuinely was stuck on "only the Sun is up there in daytime". Didn't press the issue, but always worth a laugh about it. Whatever the reason. 162.158.74.118 12:58, 3 November 2023 (UTC) Anyone want to add in any details for the Astroinertial navigation system (ANS) used by the SR-71 to plot its position during daytime? It located itself based on tracking stars (before GPS).