Wikipedia:Reference desk/Archives/Science/2022 March 6

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March 6

Milky Way size: typo or missing gloss?

Hi. Over at Milky Way, our galaxy's diameter is given as:

1. box: "Stellar disk: 185 ± 15 kly" [=170,000-200,000 light-years]
2. lead: "estimated visible diameter of 100,000–200,000 light-years"
3. size: "stellar disk approximately 170,000–200,000 light-years"

1 and 3 seem to grossly contradict 2 but I dare not fix it, as I'm wondering if "visible diameter" is supposed to be different from "stellar disk"? Like, is it a 200kly disk with only 100kly that's visible? 77.147.79.62 (talk) 19:49, 6 March 2022 (UTC)

There's a big difference between teleporting out there and looking at it with the naked eye and bringing the Hubble which can take an exposure 24 million+ movie frames long with a pupil 8 feet wide and see stars over 1 billion times dimmer than world record eyesight, the James Webb Space Telescope is even better. The James Webb sees dim stars best in near-infrared light than it does in orange and red light, this is approximately how hard it is to finally see the dimmest stars from 420,000 light years away (barely far enough to fit the whole 200,000 light years in a single photo with a normal lens (good enough to see where the stars end but not good enough to make this photo in one go as it's only 4,096x4,096 pixels which couldn't even tell one layer of stars apart (even 40,960x40,960 pixels isn't enough pixels to tell the Sun and Alpha Centauri apart if showing all 200,000 light years at once) and you'd need to take about a million photos and stitch them together because the field of view is a about a millionth of a normal camera). The radius where the galactic haloes, globular clusters and satellite galaxies fade out is really far! Sagittarian Milky Way (talk) 22:40, 6 March 2022 (UTC)

For the stellar disk, they appear to be estimates by different papers. Since the 2000s, estimates have grown from 100k to 200k ly. As for "visible diameter", I've come across only one source, which doesn't cite any references. Also keep in mind that within the Milky Way, there are dust and clouds which radiate much less energy; that could be a factor as well. GeorgiaDC (talk) 01:10, 7 March 2022 (UTC)

Atoms and molecules

What makes the atoms and molecules keep moving and from where does it come? Happh (talk) 21:13, 6 March 2022 (UTC)Happh

Heat energy. From the Big Bang. Sagittarian Milky Way (talk) 22:42, 6 March 2022 (UTC)

Wouldn't electrostatic repulsion be a better answer? Opposite charges repel attract each other. 67.165.185.178 (talk) 00:30, 7 March 2022 (UTC).

Opposite charges attract, like charges repel.--User:Khajidha (talk) (contributions) 00:44, 7 March 2022 (UTC)

What do you mean keep moving? If something with mass has initial velocity with respect to an observer, that's kinetic energy. Since total energy is conserved, it may distribute or re-distribute between different forms but never vanish. GeorgiaDC (talk) 00:47, 7 March 2022 (UTC)

Doesn't the uncertainty principle play a part as well? Clarityfiend (talk) 03:35, 7 March 2022 (UTC)

Newton's first law. It says that things continue moving unless there's something to stop them. Do you still adhere to Aristotelian physics? PiusImpavidus (talk) 10:01, 7 March 2022 (UTC)