Recent comments in /f/askscience

Aseyhe t1_j25yrby wrote

Reply to How fast does the Milky Way spin? How far does Earth move through space in a year? by Sabre-Tooth-Monkey

Most of the Milky Way galaxy, including the Sun, orbits at around 200-250 km/s; see e.g. figure 16 of this review article. Note that this implies the galaxy cannot be rotating rigidly. Objects closer to the center have shorter orbital periods.

That's about 1/1400 the speed of light, so the Sun and Earth cover about that fraction of a light year in one year, with respect to the galaxy.

Of course, all motion is relative. Why choose the Milky Way galaxy as a reference? Actually, there is a fairly natural "rest frame" for the local universe, and that's the rest frame of the cosmic microwave background (CMB). An observer in that frame finds the CMB to be equally hot in every direction. We do not, so we infer that the Sun is moving at about 370 km/s (1/800 the speed of light) with respect to the CMB rest frame.

Interestingly, that motion is anti-aligned with our motion about the galaxy, which means the Milky Way itself is moving at about 550 km/s with respect to the CMB. See table 3 of this article for more velocity comparisons; LSR is the local standard of rest, referring to the average motion of nearby stars; GC is the Milky Way galactic center; CMB is the cosmic microwave background; and LG is the local group containing the Milky Way, Andromeda, and many smaller galaxies.

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Octavus t1_j25ymfi wrote

Reply to comment by Additional-Fee1780 in What is the ‘widest’ ancestral generation? by vesuvisian

They have not been completely isolated for 50,000 years, there has been several periods of limited contact.

The most significant is ~10,000 years ago was when Australia was finally culturally split from New Guinea, there is also linguistic evidence as 90% of Australian languages are within the same family and split only a few thousand years ago. However this is before the isopoint so not related.

What is important is genetic and trade evidence between India, South East Asia, and the northwest cost of Australia. This trade and gene flow occurred ~4,300 years and gave enough time for Australia and Tasmania to become completely mixed in the 1,000-3,000 years before the contact.

This is technically only evidence of India -> Australia but the evidence points towards continue contact and not a one off event. Continued contact points to the people returning from Australia to the homelands which allows for gene flow the other direction. It simply takes one person to make the trip and have descendants.

The dingo has only been in Australia for 4,000-10,000 years. If Australians have been isolated for 50,000 years where did this non-native animal come from?

Genome-wide data substantiate Holocene gene flow from India to Australia

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Tidorith t1_j25vo9s wrote

Reply to comment by YoureSpecial in How do shifts work on really long medical operations? by TerjiD

>IIRC the Navy did a couple studies after a rash of collisions and other ship casualties. The net result was to shorten the shifts in certain critical command/control positions - Officer of the Deck, Navigator, helmsman, Weapons Officer, etc.

Perhaps the takeaway really is that we need to invest significant resources into developing better procedures for hand offs that mitigate the negative consequences of them. Then we can shift the equilibrium closer to optimising for the first order effects of shift length itself.

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Spanks79 t1_j25uy96 wrote

Reply to comment by Additional-Fee1780 in What is the ‘widest’ ancestral generation? by vesuvisian

Yes, as I state in my post other DNA might still be mixed in into the lines. As the egg organelles come from eve, there might be much different dna in the chromosomes.

Same for the male thing.

Actually there’s many humans with Neanderthal and Denisova dna. Interbreeding took place and introduced different dna.

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