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  1. #861

    DART Hindsight

    Remember DART?

    The crashing of a satellite into an Asteroid (Dimorphos) to see if it's orbit can be perturbed?

    Here is more information about what was learned from that mission:
    https://www.msn.com/en-us/news/other...9641b4f3&ei=22

    Toward the bottom are URLs to the Abstracts of scientific papers analyzing results.

    Larry
    DevilHorse

  2. #862

    What Time Is It On The Moon?

    Read an interesting (short) discussion on what time it is on the moon ('now' is not accurate enough ).
    https://www.interestingfacts.com/fac...d851000877295a

    Interesting things to think about are:
    1) Time Flows differently on another planet or moon because of General Relativity.
    This problem with clocks surely can be compensated for with computers
    3) Will they set an independent Lunar/Planet time or just re-use earth time (UTC)?

    For those looking for perspective on the slower time on the moon [item 1) above] (time on the moon slips 56 microseconds slower per day), that converts to a 1 second slower figure every 50 years.

    Other thoughts:
    + Why do they need to have a smooth clock sync between earth and any celestial object. The effect is small enough that you can re-sync once a day and not lose much accuracy. Or just resync clocks to match the tolerance you need for GPS.
    + Keeping track of calendar 'days' or sols doesn't have to wedded to 'Time'.
    + Other effects will also change the timing. Tidal forces between a planet and moon slow down the rotational period of both, and change the distance between them (length of a 'year'/ one rotation). Re-sync's, like leap seconds, will always be necessary.
    + What happens to circadian rhythms? More than you'll ever want to know here: https://www.sciencedirect.com/scienc...22283620302308
    + geosynchronous satellites for earth are at a 37,000 km radius (just under 23,000 miles); geosynchronous satellites around the moon are at 88,441 km (almost 55,000 miles).
    + GPS satellites circle the Earth at an altitude of about 20,000 km (13,000 miles) and complete two full orbits every day (not geosynchronous).

    More discussion and information here:
    https://www.space.com/does-moon-need-its-own-time-zone

    Larry
    DevilHorse
    Last edited by DevilHorse; 03-07-2023 at 09:56 AM.

  3. #863
    Join Date
    Feb 2007
    Location
    Washington, DC area
    Nice rundown! Count me in the UTC camp. Keep it simple.

    -jk

  4. #864

    Things In Our Universe

    Interesting article about large structures (very far away) in our Universe that are unexpected under the present theories:
    https://www.bbc.com/future/article/2...b-e38d2e632a77

    It is impressive that Astronomy continues to evolve at a great pace.

    Larry
    DevilHorse

  5. #865
    Quote Originally Posted by -jk View Post
    Nice rundown! Count me in the UTC camp. Keep it simple.

    -jk
    As a practical matter, I would imagine that a moon base (or Mars base) might use 2 clocks; one for local time to adapt to practical circumstances and routines, and a Universal Time clock to sync with Earth when communicating or transporting. But as Einstein pointed out in his observations of relativity, being far apart and having the same clock time still poses a problem of cataloging and coordinating events. From the Earth to the moon, it is (only) a 1.3 second difference to send/receive a message or observe a phenomenon. The fastest a message can be sent to Mars from Earth (when they are the closest) is 3 minutes and 22 minutes when they are farthest apart. New strategies for communicating will have to become commonplace.

    Larry
    DevilHorse

  6. #866
    Join Date
    Feb 2007
    Location
    Washington, DC area
    Quote Originally Posted by DevilHorse View Post
    As a practical matter, I would imagine that a moon base (or Mars base) might use 2 clocks; one for local time to adapt to practical circumstances and routines, and a Universal Time clock to sync with Earth when communicating or transporting. But as Einstein pointed out in his observations of relativity, being far apart and having the same clock time still poses a problem of cataloging and coordinating events. From the Earth to the moon, it is (only) a 1.3 second difference to send/receive a message or observe a phenomenon. The fastest a message can be sent to Mars from Earth (when they are the closest) is 3 minutes and 22 minutes when they are farthest apart. New strategies for communicating will have to become commonplace.

    Larry
    DevilHorse
    Local time? One that coordinates with whatever earthly nation/base they work most closely? (Or a moon "day" of a month?)

    -jk

  7. #867
    Quote Originally Posted by -jk View Post
    Local time? One that coordinates with whatever earthly nation/base they work most closely? (Or a moon "day" of a month?)

    -jk
    It isn't obvious to me why a 24 hour day is required. A routine is important IMHO.

    For example, the Martian Sol is 24 hours, 37 minutes, and 22 seconds long.
    I would get a Mickey Mouse watch that is adjusted to 24/37/22 to give it 24 MarsHours so I could have sunrise/sunset once a day, not sliding an hour every 2 days.

    Just my vision of what a day on another planet might be accomplished.

    Larry
    DevilHorse

  8. #868
    Join Date
    Sep 2007
    Location
    Undisclosed
    Quote Originally Posted by DevilHorse View Post
    It isn't obvious to me why a 24 hour day is required. A routine is important IMHO.

    For example, the Martian Sol is 24 hours, 37 minutes, and 22 seconds long.
    I would get a Mickey Mouse watch that is adjusted to 24/37/22 to give it 24 MarsHours so I could have sunrise/sunset once a day, not sliding an hour every 2 days.

    Just my vision of what a day on another planet might be accomplished.

    Larry
    DevilHorse
    Submariners use an 18-hour day (air at least they used to) ó 6 hours work, 6 hours relax, 6 hours in the bunk. Time is free.
    ďI do not think that word means what you think it means.Ē

  9. #869
    Join Date
    Feb 2007
    Location
    Washington, DC area
    Quote Originally Posted by DevilHorse View Post
    It isn't obvious to me why a 24 hour day is required. A routine is important IMHO.

    For example, the Martian Sol is 24 hours, 37 minutes, and 22 seconds long.
    I would get a Mickey Mouse watch that is adjusted to 24/37/22 to give it 24 MarsHours so I could have sunrise/sunset once a day, not sliding an hour every 2 days.

    Just my vision of what a day on another planet might be accomplished.

    Larry
    DevilHorse
    Mars is an entirely different issue v. the Moon. There's no meaningful day on the Moon.

    Quote Originally Posted by OldPhiKap View Post
    Submariners use an 18-hour day (air at least they used to) ó 6 hours work, 6 hours relax, 6 hours in the bunk. Time is free.
    That must really mess with the circadian rhythm!

    -jk

  10. #870
    Quote Originally Posted by OldPhiKap View Post
    Submariners use an 18-hour day (air at least they used to) — 6 hours work, 6 hours relax, 6 hours in the bunk. Time is free.
    Interesting. I wonder what the effect is on the Circadian Rhythms.

    Wow, here is the answer to my question:
    https://mmrjournal.biomedcentral.com...79-020-00268-2

    Larry
    DevilHorse

  11. #871
    Quote Originally Posted by -jk View Post
    Local time? One that coordinates with whatever earthly nation/base they work most closely? (Or a moon "day" of a month?)

    -jk
    It's not local [calendar] time that is really at issue, but local [physical] time. Local calendar time might be "complicated" to calculate, but it's trivially solved by a handful of smart people and the solution adopted/handed off to the unaware thereafter, including syncing with the Earth, probably using UTC or something similar (I suspect it would be an easy Schelling point). The issue is having two time standards simultaneously for both calendar and measurement. Measurement by itself, both on small and large scale, is similarly trivial if adopting a well thought-out solution - you could even adopt the same strategy used on Earth, redefining a unit we already have in terms of a physical quantity (look up SI standards for time/seconds and cesium, or the kilogram or meter for comparable examples), but there would be a corresponding discrepancy between the two in a way somewhat analogous to how weight and mass differences start to actually matter when you're not confined to our lovely home any longer.

    Of course there is nothing preventing two standards for two similar sorts of things, but people will naturally make a fuss about it and also make errors confusing the two.

  12. #872
    Join Date
    Feb 2007
    Location
    Washington, DC area
    Quote Originally Posted by BLPOG View Post
    It's not local [calendar] time that is really at issue, but local [physical] time. Local calendar time might be "complicated" to calculate, but it's trivially solved by a handful of smart people and the solution adopted/handed off to the unaware thereafter, including syncing with the Earth, probably using UTC or something similar (I suspect it would be an easy Schelling point). The issue is having two time standards simultaneously for both calendar and measurement. Measurement by itself, both on small and large scale, is similarly trivial if adopting a well thought-out solution - you could even adopt the same strategy used on Earth, redefining a unit we already have in terms of a physical quantity (look up SI standards for time/seconds and cesium, or the kilogram or meter for comparable examples), but there would be a corresponding discrepancy between the two in a way somewhat analogous to how weight and mass differences start to actually matter when you're not confined to our lovely home any longer.

    Of course there is nothing preventing two standards for two similar sorts of things, but people will naturally make a fuss about it and also make errors confusing the two.
    Aren't we already doing that sort of calculation with our satellites that have a tiny (dare I say "minute") time shift in orbit? I thought the discussion is more "Pick a standard. Any standard." so everyone's stuff can work together there.

    -jk

  13. #873
    Quote Originally Posted by -jk View Post
    Aren't we already doing that sort of calculation with our satellites that have a tiny (dare I say "minute") time shift in orbit? I thought the discussion is more "Pick a standard. Any standard." so everyone's stuff can work together there.

    -jk
    I'm sure that any standard CAN be adopted, but it probably has benefits and detriments to different groups. I'm sure there are lots of views on what dependence on clocks will be from time consumers (all kinds of different satellites, astronauts/planet_dwellers, earth based scientists/bases). If there were no advocates for these different positions, the answer would be easy.

    I think about setting up rules for the engagement of Antarctica. There were lots of claims on the land, but agreements evolved for access and use of the territory. One Time Zone (New Zealand) was agreed on. There are obviously some different issues. The moon, like Antarctica, has no indigenous human population.

    Both legal and scientific compromises are going to be inevitable, and there will surely be lots of opinions.

    Larry
    DevilHorse

  14. #874
    Join Date
    Feb 2008
    Location
    New Bern, NC unless it's a home football game then I'm grilling on Devil's Alley
    New Moon suits revealed.
    The new design, which looked black with blue and orange detailing for the unveiling, appeared to take on a vastly different aesthetic than the puffy white suits worn by moonwalkers of the 20th century. However, Axiom Space noted in a news release that its suits are covered in an extra layer — bearing the company’s colors and logo — for display purposes.
    The actual spacesuits worn by astronauts must be white “to reflect heat and protect astronauts from extreme high temperatures,” according to the release.
    https://www.cnn.com/2023/03/15/world...scn/index.html

    230315091725-03-axiom-space-suit.jpg
    Q "Why do you like Duke, you didn't even go there." A "Because my art school didn't have a basketball team."

  15. #875

    The Latest From the Outer Solar System

    A few new things about the outer solar system, courtesy of New Horizons:
    https://www.msn.com/en-us/news/techn...fa50547a&ei=18

    And a bit closer to home, (yet) another near-earth asteroid is passing between the moon and the earth later this evening:
    https://www.msn.com/en-us/news/techn...cc5e5005&ei=14

    Larry
    DevilHorse

  16. #876
    People really worry about the length of a day:
    https://www.msn.com/en-us/news/techn...4ac4ce2a&ei=23

    Larry
    DevilHorse

  17. #877

    Once In A Decade NEO

    A football field sized asteroid will be passing between the earth and moon on Saturday. 100k miles away is not that forboding. However, as with other Near Earth Asteroids (NEOs) they too are orbiting the sun with an orbit somewhat approximate to our own (relatively). So they expect a revisit in 2046, although the orbit needs great refinement, no doubt after its close encounter with the earth/moon system.
    https://www.msn.com/en-us/news/techn...dcf2e0d0&ei=19

    Although this asteroid was discovered just months ago, it's nice to know that we will have a much more matured DART backing us up.

    Larry
    DevilHorse

  18. #878
    Quote Originally Posted by DevilHorse View Post
    A football field sized asteroid will be passing between the earth and moon on Saturday. 100k miles away is not that forboding. However, as with other Near Earth Asteroids (NEOs) they too are orbiting the sun with an orbit somewhat approximate to our own (relatively). So they expect a revisit in 2046, although the orbit needs great refinement, no doubt after its close encounter with the earth/moon system.
    https://www.msn.com/en-us/news/techn...dcf2e0d0&ei=19

    Although this asteroid was discovered just months ago, it's nice to know that we will have a much more matured DART backing us up.

    Larry
    DevilHorse
    Letís say we know an asteroid like this is going to hit us. With current technology - in the last week or couple of days we will be able to calculate where on earth it will hit, right? Or wrong? Assuming we can, imagine the scramble for airline tickets and the jammed roads as everyone tries to vacate the predicted landing area! I ainít waiting- Iím booking my plane tickets as soon as they speculate it might hit the earth. I can always cancel my flight if they end up deciding it will miss my part of the world.

    See, Iím always thinking ahead!

  19. #879

    Oumuamua Again

    The latest from outside the solar system:
    https://www.wsj.com/articles/mysteri...le_email_share

    Latest thinking is that Oumuamua is a funky comet.

    Avi Loeb disagrees (because it isn't proof that it is NOT an alien ship).

    Larry
    DevilHorse

  20. #880
    Devilhorse - Iím curious if you know or can figure out the answer - how far out would we know *where* an asteroid headed for earth would hit? When would we know it was likely to hit China vs North America vs Australia, etc? Would we be able to predict say, what country it will hit a day or two before it struck? This seems like it would be right up your ally.

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