A Day on Mercury – 60 Second Adventures in Astronomy (4/14)

By | December 5, 2019

60-Second Adventures in Astronomy. Number
four: a Day on Mercury. No two planets act exactly the same whether it’s Jupiter
spinning in only 10 hours, Venus spinning backwards or Uranus tilting to one side.
But Mercury is particularly strange, it takes nearly 59 Earth days to rotate,
which might make for a pretty long day but at least you’d have time to get
things done. But while the days are long on Mercury, the years are relatively
short, it travels around the Sun in just 88 Earth days. Now until 1965 we thought
Mercury span exactly once per orbit, which would mean that one side of it was
always facing the Sun. If it span twice every orbit its day would be the same
length as its year, which would at least make calendars nice and simple. But it
actually spins three times for every two orbits which means each Mercury day
lasts for two Mercury years, so while you might get a bit bored waiting for the
evening at least you’ll be able to celebrate your birthday twice a day. Even
if you had to share it with everyone else.

33 thoughts on “A Day on Mercury – 60 Second Adventures in Astronomy (4/14)

  1. JP Major Post author

    Uranus. It's tilted more than 90º on its side. (And yes, LOL.)

  2. Phillip S Post author

    The video states that Mercury "spins 3 times every 2 orbits which means that each Mercury day last 2 Mercury years."

    Shouldn't that be 3 days every 2 years or each Mercury day lasts 2/3 of a Mercury year?

  3. David Rothery Post author

    No. It's hard to get your head round, which is whjy we made this video. If Mercury wasn't rotating at all, the Sun would move (backwards) round Mercury's sky once per orbit. If Mercury span once per orbit, the day would be infinitely long (the Sun wouldn't move in Merciry's sky at all, as said at 47s in the video). If Mercury rotated twice per orbit there'd be one day per year. 3 rotations per 2 orbits (or, if you prefer, one and a half rotations per orbit) results in one day per year.

  4. Seoul Assassin Post author

    I'm confused by this: "If Mercury rotated twice per orbit there'd be one day per year."
    Doesn't 1 rotation = 1 Mercury day?
    So if it rotated twice per orbit, wouldn't that mean there's 2 days per year?

  5. David Rothery Post author

    Watch it again carefully, and listen well to what that nice Mr Mitchell says 😉

  6. David Rothery Post author

    No. The video is correct. Two spins per one orbit would result in one day per year. Three spins per two orbits results in one day per two years. The spin of a planet is always measured relative to the universe at large, not relative to the star that it orbits.

  7. David Rothery Post author

    Thank you Mani. We would be glad for it to be used in any way. May I ask which program you teach?

  8. Kenneth Roberts Post author

    @1:19"…or ur anus, tilting to one side…." yes i know im 5 years old, but thats some funny shit.

  9. ASTV TEAM Post author

    Gimme narration script plssss
    I didnt catch your word

  10. Astrolekker Post author

    Check out my channel for videos relating to Astronomy! 🙂

  11. M1zzu q Post author

    doesn't change the sun its direction about thrice a "day" as well?

  12. Wilder Post author

    If mercury was ever successfully colonized (not even remotely possible, but imagine) it would be the Mardi Gras planet, because of the days to years ratio.

  13. OperatorOn5thStreet Post author

    Your anus tilting to one side… Oh god, I can't unhear that anymore.

  14. orochimarujes Post author

    I like how this video turned our Earth-based timekeeping on its head. I suppose we forget that day<year is not universal.

  15. Amine Aboutalib Post author

    think of it as every spin cancels the effect of the planet orbiting so it's just like it's stationary and the left spins are actual days . So one spin for one orbit cancel each others out and the planet doesn't move thus the day is infinite , two spins for one orbit , one cancels the orbit and thus the planet is stationary with one left spin , one day for one orbit , thus one day for one year , three spins for two orbits , well u get the idea , one day for two years.

  16. Aspie Mt69 Post author

    Even Professor Hawking laughed at a Uranus joke, i think. I 'm glad that I decided to study history because I'd be laughing every time the lecturer mentions Uranus.

  17. AXZ1974 Post author

    Question: According to http://scienceworld.wolfram.com:
    "The day is (roughly) defined as the time required for the Earth to complete a rotation." This rotation "is always measured relative to the universe at large", as David mentions in his comment, but no matter how we measure it, the fact is that a day is a complete rotation. So, isn't that the amount of time that it takes for your zenith to point to exactly the same place in the sky two consecutive times? Isn't that what a day is?
    So I am thinking, the same should apply to any planet (am I wrong?). And if a planet rotates once for every orbit around the Sun, doesn't that mean that for your zenith to point to exactly the same place in the sky, it takes exactly one of your planet's years? So that one planetary day is also one planetary year?
    Can anyone explain why the video says otherwise?
    (obviously, it shouldn't matter if during the day in question, the luminosity at each point on the planet's surface stays (more or less) the same)

  18. RayRay 711 Post author

    I usually get annoyed with the Uranus jokes. It just seems overplayed and childish, although, the way the narrator said "UrAnus tilted to the side", I cracked a slight smile.


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