Dr James O'Donoghue

@physicsJ

Planetary Scientist , previously . Jupiter & Saturn, rings, aurora & making animations. 🇬🇧 in 🇯🇵. Tweets mine

Tokyo, Japan
Vrijeme pridruživanja: prosinac 2010.
Rođen/a 1985.

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  1. Prikvačeni tweet
    30. ruj 2019.

    Light Speed – fast, but slow

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  2. proslijedio/la je Tweet
    prije 18 sati

    This majestic, large-end side view of comet was taken by in 2015

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  3. proslijedio/la je Tweet
    2. velj

    230 million years it takes the solar system to orbit the Milky Way center, and nearby stars mostly co-orbit with our solar system so it's a slow and minor change That said, some stars are fast moving nearby – high "proper motion" stars Here's Barnard's star, 6 light years away

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  4. proslijedio/la je Tweet

    If you hear someone crying in the hallway at NASA it’s me because I GOT MY FIRST GRAD SCHOOL OFFER FOR A PHD IN PLANETARY SCIENCE 😭

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  5. prije 19 sati

    Coming sometime this week: An animation to explain leap years!

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  6. proslijedio/la je Tweet

    In my Hubble Space Telescope calendar, the image for February is: Arp 142 - Penguin and Egg ....adorable! 🥺✨😍💕

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  7. prije 20 sati

    Saturn's northern pole is v pretty Made with NASA/Cassini/SSI/Taxpayer imagery 🚀🚀🚀

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  8. prije 21 sat

    Thanks very much for all your positive replies to this, looks like this really clicked with a lot of you (gained an unusually high number of new followers for this fairly non viral tweet)

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  9. prije 21 sat
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  10. proslijedio/la je Tweet
    2. velj

    Someone asked me to do an explainer for why we only see one side of the Moon, showing that it still rotates. Well, accumulating so many animations now that I can say "here's one I made earlier!" –

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  11. proslijedio/la je Tweet
    2. velj

    Earth physically rotates in 23hours 56min relative to distant stars – a Sidereal Day, BUT it takes 24hours to rotate relative to the Sun – a Solar Day The difference? Earth orbits the Sun, so the Sun appears to move (down, in the vid), which means Earth needs +4mins to catch up!

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  12. 2. velj

    And... even a southern hemisphere perspective version!

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  13. 2. velj

    Someone asked me to do an explainer for why we only see one side of the Moon, showing that it still rotates. Well, accumulating so many animations now that I can say "here's one I made earlier!" –

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  14. proslijedio/la je Tweet
    2. velj
    Odgovor korisnicima

    Sun rotates in around 25 days at its equator, but about 35 days at the poles Since the Sun rotates in the same sense as Earth, we could feasibly keep track of a feature (like a sunspot) for about 1.25 days longer

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  15. 2. velj

    Image credit (Steve Quirk) and more info:

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  16. 2. velj

    230 million years it takes the solar system to orbit the Milky Way center, and nearby stars mostly co-orbit with our solar system so it's a slow and minor change That said, some stars are fast moving nearby – high "proper motion" stars Here's Barnard's star, 6 light years away

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  17. 2. velj

    366 sidereal days in 365 solar days By the time Earth has rotated 366 times relative to the stars, we've also seen the Sun "appear" to do a lap around Earth The Sun-lap makes it look like only 365 rotations were completed

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  18. 2. velj

    Fun twist: if we orbited the Sun clockwise instead of counter-clockwise, we would have a 23hr 52min Solar day So instead of "gaining" 4 minutes like we are now – relative to the Sidereal day – we would "lose" 4 minutes.

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  19. 2. velj

    Earth's "real" day is 23hr 56min (sidereal day) However, every single day it takes us an extra 4 mins to catch up with the Sun because we move about 1° in our 360° orbit per day, so we call our day 24hrs So... you are all already getting the benefit of an extra 4minutes per day

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  20. 2. velj

    *sigh* there aren't enough hours in the Sidereal day

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  21. 2. velj

    If Earth did NOT orbit the Sun, then both Sidereal and Solar days would equal 23hr 56min. We wouldn't have a year at all, and would slowly be pulled into the Sun... which would be Unreal

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