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

[@sliver170]

I like how this video turned our Earth-based timekeeping on its head. I suppose we forget that day

[@daveroth1956]

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.

[@Keithustus]

So are you saying that one day on Earth’s moon, relative to Earth and not the sun, is infinitely long?

[@impossibleman]

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?

[@PuckLokin]

Because the direction of the Sun changes as you move around it you get more free hours each Solar Day. 3 Spins in 2 Orbits = 1.5 Spins in 1 Orbit, ye? From one fixed spot on the surface it takes half that orbit for the sun to just set, and by the end it's midnight. If it were spinning the other direction you'd get way less hours each Solar Day, way more Solar Days per year. Get a marker and draw a house on a ping pong ball and roll that along the outside of a tennis ball. You move a decent way around it before the house no longer has line of sight to the tennis ball. The trick here is that there's a Solar Day, which is sunrise-to-sunrise (or whatever), and Sidereal Day, which is one full spin on the axis of rotation. They're not the same length. If they were you'd either not be moving around the sun at all somehow, or... uh... I think that's the only way you'd have that? Anybody else got something for that?

[@lifescience4all]

Awesome video, I am planning use for my program

[@daveroth1956]

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

[@amineaboutalib]

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.

[@RACookPE1978]

No, that is not correct. The sun "rises" on Earth_day_nbr-1. It slowly crosses the sky, going higher every 24 earth-hours for 44 earth_days, then on earth_day_44 it is at "noon" - its highest elevation point in the sky at that latitude. From earth_day_45-earth_day_88, the sun moves (slowly!) downward towards the horizon. At earth_day_89, the sun is below the horizon all 24 earth_hours. From earth day_89 through earth_day_176, it remains below the horizon. On earth_day_176 (two 88 sun-lit periods), the sun begins to rise again from the eastern horizon.

[@daveroth1956]

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.

[@laikwanwong5241]

I am confused as well, here is how I understood: when 1 orbit = 1 year and 1 spin = 1 day, TIme used for 3 spins = 2 orbits, thus, 1.5 spins = 1 orbit, hence, 1.5 days = 1 year Conclusion: My understanding is 1 Mercury year = 1.5 Mercury days

[@TraceurNath]

In fairness, the video offers no explanation as to why. Having those facts with no background info heavily implies causation.

[@JMajorLITD]

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

[@chewie481]

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

[@gpcrawford8353]

Keep these educartoons coming hilarious.

[@AXZ1974]

Question: According to 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)

[@Keithustus]

Sounds like they’re talking about solar days and you are referring to sidereal days.

[@PuckLokin]

@@Keithustus Sounds like they were re-discovering the need for having that distinction, and coming up with a working definition for Sidereal Days, yea. Good brain-ing.

[@StardustScribe]

yes

[@RichardRicciardelli]

Probably!

[@ShadeOnTheUtube]

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.

[@dkolaczynski]

Each of our gas giants has rings.

[@Gytax0]

0:19 Uranus or Saturn?

[@Benjamin-pg7jq]

Your anus

[@Keithustus]

Definitely Uranus. Saturn isn’t tilted funny like that and has a much wider ring system.

[@Gytax0]

@@Keithustus Thanks for the quick response!

[@Keithustus]

7777777, gotta love YT. Anywhere else online it’s useless responding to years’ old comments.

[@skyopeia]

Is that David Mitchell narrating?

[@TheCreatorofGood]

Dame Mercury you scary!

[@Hobluj23]

Uranus have a ring system too

[@daveroth1956]

Watch it again carefully, and listen well to what that nice Mr Mitchell says ;-)

[@palakuls]

Gimme narration script plssss I didnt catch your word

[@ivanhribar1]

LOL

[@jerboas]

This is 83 seconds

[@MrenderboyoOld]

Lol

[@RayRay-zt7bj]

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.

[@camelCaseFTW]

moo