Talk:Day

Relevance of the picture of the Bay of Naples

I question the validity of singling out that shot as relevant to the entry. I read through for any mention to the city or the bay itself and since there was none, I suggest its removal as irrelevant. Maringaense 00:13, 29 September 2018 (UTC) — Preceding unsigned comment added by Maringaense (talk • contribs)

A Commons file used on this page or its Wikidata item has been nominated for deletion

The following Wikimedia Commons file used on this page or its Wikidata item has been nominated for deletion:

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Participate in the deletion discussion at the nomination page. —Community Tech bot (talk) 22:39, 7 January 2022 (UTC)

How could we expand on this article?

PerfectSoundWhatever, this is a really difficult and amorphous topic to expand upon. What should we do first? CactiStaccingCrane (talk) 11:37, 19 August 2022 (UTC)

We should increase citation density, which will increase the amount of bytes. For example, the section Apparent and mean solar day could use a rewrite with more citations. Leap seconds is entirely unsourced. The longitudal change thing is super interesting, we could have some prose to go along with that table. I could attempt to try to translate some of that paper, not sure how that will go, but it'd be a better idea to find other sources about the subject (and make sure that it actually is a thing). For new sections? Maybe parts of the day and their cultural implications could be added. No parts of the day article exists anywhere on wiki afaik. — PerfectSoundWhatever (t; c) 13:29, 19 August 2022 (UTC)

I agree, let's do it then :) CactiStaccingCrane (talk) 13:31, 19 August 2022 (UTC)

"The Earth-Moon system is not in the Hubble flow"

@Thucydides411: do you have a source that disproves that the Earth-Moon system is not impacted by the expansion of the Universe, as stated in this source? I am far from an expert in the subject matter, so my only way to research is to go off of papers that I can find, so sorry if the statement is incorrect. But I'd like to see proof before removing the statement entirely, thanks! — PerfectSoundWhatever (t; c) 16:02, 22 August 2022 (UTC)

@PerfectSoundWhatever: Hubble's law (of expansion of the universe) only applies on large scales - far larger than the scale of a galaxy, not to mention the Solar System. The "Hubble flow" is a term for the distant universe, where expansion begins to take effect. At smaller scales, gravitational interactions between stars, planets, etc. dominate, and the Universe isn't homogeneous, so the assumptions of cosmological theory don't even hold. Cosmology describes what happens on very large scales, not on the scale of the Solar System, or even of the Milky Way.

Any basic text on cosmology will cover this, but I'll link to a review article on the Hubble constant here. You can see that it discusses the "Hubble flow", and the fact that it only begins at approximately Megaparsec scales (i.e., many orders of magnitude larger than the distance between the Earth and Moon).

If you're not satisfied with this source, my one plea is not to re-add the claim about the distance to the Moon being affected by cosmic expansion unless you can find much better sourcing than what was previously used (and I'm fairly confident you won't find better sourcing, because the claim is incorrect). -Thucydides411 (talk) 08:54, 23 August 2022 (UTC)

Since the expansion of the universe is now supposed to be caused by the cosmological constant it applies at all scales. Perhaps the previous section means to say that it has no measurable effect on the small scales mentioned.−Woodstone (talk) 16:18, 23 August 2022 (UTC)

Thank you for the detailed reply, @Thucydides411:. This level of study really goes over my head. I found a discussion in the comments of the first answer here [1] and looked at some of the linked papers.This paper seems to say that Hubble expansion affects the Moon-Earth system. Could you please verify if this is correct? Another paper linked states "The effect on the orbit is insignificant as are the effects on the galactic and galactic--cluster scales". I am quite confused as to whether there is a scientific consensus on the topic. It appears muddled, so of course, the statement should be left out for now. Just wanted to additionally send those papers. — PerfectSoundWhatever (t; c) 19:39, 23 August 2022 (UTC)

@Woodstone: The cosmological constant is one hypothesis for the cause of the expansion, but there are also different hypothesized forms of dark energy. The cosmological model assumes a homogeneous matter distribution and constant spatial curvature, neither of which is satisfied on small scales (below a few Megaparsecs). The cosmological model only applies on scales many orders of magnitude larger than the Solar System, so it's meaningless to talk about cosmic expansion inside the Solar System. In any case, I think this sort of speculation is esoteric enough that it should not be included in this article. -Thucydides411 (talk) 18:31, 24 August 2022 (UTC)

Agreed that it does not make sense to mention expansion of the universe as influencing length of day here. However saying categorically that it does not apply on certain scales makes no sense either. Natural laws are universal. Effects of them may not be measurable (relevant) on certain scales.−Woodstone (talk) 08:32, 25 August 2022 (UTC)

My point is that the standard cosmological model doesn't not apply at all on the scale of the Solar System. It assumes a homogenous distribution of matter and constant spatial curvature. Neither of those conditions is met in the Solar System. -Thucydides411 (talk) 12:10, 25 August 2022 (UTC)

Names?

Suggestion:

shouldn't the names of each day of the week be mentioned here somewhere? Maybe a link the article Names of the days of the week. 94.252.6.224 (talk) 19:28, 18 October 2023 (UTC)

Revert

I reverted this edit because the article is Day, not Earth's rotation. The previous pictures were a better illustration of the concept than a picture of the Earth spinning. Note in particular that the face of the Earth in the animation is fully lit, so it does not even illustrate how the day/night cycle arises. Srleffler (talk) 01:09, 30 October 2023 (UTC)