UKH

So this is a trick question and the answer using my trickery is 7.

Can anyone explain why?

Pluto is a dwarf planet so doesn't count. Mercury is locked gravitationally so its day is equal to its year so it revolves around the sun. Oh I don't know! Has Mercury been demoted too?

As far as I am aware, mercury is still a planet and is one of the seven.

I'm not happy about the demotion, but my answer goes along with Pluto not being a planet.

Answers that are arguably correct are eight, between 13 and 18, or absolutely loads.  Depends on your definition of where the line between dwarf planet and minor planetary body lies.

I don't know of any logical way to make the answer seven.  Are you excluding Mercury on the basis that it's quite eccentric, or that it's smaller than Titan and Ganymede?

The only other 'oddball' I can think of is Uranus because of its axial tilt (effectively rotating 'on its side'). Does that count it out?

No

No

Because Jupiter is a failed star?

The ancient Greeks called the oddly moving bodies they could see 'planetes' ('wanderers'). Earth evidently doesn't wander so wasn't classed by them as a planet. Pluto isn't nowadays a planet. That makes seven.

I like your thinking but Earth is one of the seven.

You're very close, why might this failed star not be a planet that orbits around the sun. It is a planet however.

It's Jupiter, because it's so massive, it (and the sun) orbit a point close to the sun.

bingo

Got it! Jupiter orbits about a point which is outside the actual body of the sun. None of the other planets do. So discount Pluto and Jupiter. Drat, pipped at the post!

As usual, it’s something to do with Uranus.

At least this time he's presented something truthful (dare I say even interesting!) and without an entirely misleading slant to misrepresent reality!

But Jupiter still orbits round the Sun, which is what the original question addressed. The fact that the centre of the orbit is offset by the mass of Jupiter is a secondary consideration.

It orbits around a point in space that has nothing in it. So it orbits around nothing.

........

and the sun, and the sun orbits around Jupiter, and every other planet for that matter.

Actually, they've over-simplified the issue to the point that they're currently wrong...  

Two bodies in isolation orbit their centre-of-mass (or barycentre).  If you consider a single planet and the sun in isolation, most of the planet-sun pairs have the barycentre within the sun, so whilst technically the sun and the planet are both orbiting the barycentre, this is reasonably well described as the planet orbiting the sun as the point being orbited lies within the sun - although the sun also orbits this point.

The isolated system of the sun and Jupiter is an exception, with the barycentre falling at 1.07x the solar radius, meaning that they both orbit a point in free space.

However, what actually happens is that all the heavenly bodies - including the sun - orbit about the barycentre of the whole system.  

The location of the solar system's barycentre varies with the position of all the planets etc, and hence with time.  Sometimes it's within the sun and sometimes it outwith the sun.  

So, at times, no planets orbit the sun (as they orbit the barycentre outwith the sun), and sometimes all planets and the sun orbit a point within, but not at the centre of, the sun (when the barycentre is within the sun).  I would argue it's a semantical stretch to say they're actually orbiting the sun, but that stretch is only possible when the barycentre is within the sun.

Right now I believe the barycentre lies beyond the sound's radius and so nothing is orbiting the sun.  Everything is orbiting the centre of mass of the system and that point is not encompassed by the sun.

• https://commons.wikimedia.org/wiki/File:Solar_System_Barycenter_2000-2050.p...

Of course, we all knew that, it's common sense, I was merely humouring montyjohn.

Gave me an idea though - we should have planet-wide days of celebration when the barycentre re-enters the sun and planet-wide days of dirge when it leaves the sun.  What a spectacular astronomical event to celebrate.  

Next celebration is due circa March 2027.  I'll put that in my calendar...

(*) with a slight semantic stretch.

2030 to truly put my OCD to rest.

PS the Solar System's on the p*ss!

One party for re-entering the sun and another for reaching the point of closest approach to the solar centre on that epicycle?  

There's a kind of seasonality to it with the entry and exit resembling the equinoxes, and the closest and most distant points on an epicycle resembling the solstices in terms of the heat at the barycentre.  I like that way of thinking about the process.

Hmm.  Wouldn't you agree that two dance partners do-si-do around each other?

Great trick question.

However: did you know that there are rings around Uranus?

Surely a dwarf planet is still a planet. Just like a gas giant planet is still a planet.

I like to go back to the origin of the word, which is the Greek for “wanderer”, because they were observed to wander with respect to the fixed stars.  Pluto meets that description.

I think they had to create this new category to prevent the number of official planets mushrooming. There could be a lot of Pluto-sized bodies orbiting out there. Something about sweeping out all other debris along its orbit as well which apparently Pluto doesn't do? Whatever the reasons Pluto turns out to be a fantastically interesting place anyway.

That reminds me. Wasn't the spacecraft that visited Pluto going on to a smaller one? Has it reached it yet?

No it doesn't. The (ancient) Greeks didn't observe Pluto, and most modern observers would still struggle. 

And plenty of other bodies - comets for example - wander far further than the accepted 'Planets'. 

Nor did they observe either Uranus or Neptune.

It’s not “wandering in distance” they observed so it’s not about “far father”, but that the observable motion across the sky of the planets they could see wandered with respect to the fixed stars on the view of the sky.  The distant planets and dwarf planets meet that description if you have the means to see objects of their relatively constant brightness. Unlike comets.

I'm waiting for Jupiter being likened to the mighty UK, and it being able to go it alone without being controlled by the rest of the solat system.

Well, they did get to name it after Mickey Mouse's dog

I thought so too but according to  https://solarsystem.nasa.gov/missions/new-horizons/in-depth/  it's in the Kuiper Belt in hibernation mode ('to save fuel and wear and tear on the spacecraft'). Apparently, it flew 2,200 miles away from something called Arrokoth on 1/1/19. There's no mention of it heading for any particular target just now.

Ah, thanks. Reading that it seems that Arrokoth was what I was thinking of though it hadn't been named at the time.

Good news: we're now free to source our energy from Neptune given that we've cut our ties with the sun. And you can be sure that the sun will miss us more than we miss it.

And we'll be able to send all the Martians back to Mars where they belong.

I've just googled for Arrokoth and it seems that it was originally designated 'Ultima Thule'. That was the name I recall hearing as the next target beyond Pluto. When you see the pictures I think they should have renamed it 'Frosty'

https://www.nasa.gov/feature/far-far-away-in-the-sky-new-horizons-kuiper-be...

Yes, that rings a bell.

Speak for yourself!

In reply to sweetcake:

True story:
youtube.com/watch?v=k4Ar67rTO_w&

sounds like a home for Arachnids

Want to know more?

No, they're all moving in with me at the moment

Do you have inside knowledge that NASA aren't sharing (along with alien bases on the Moon)?

Cool reference citizen - hopefully not just a coincidence in turn of phrase

indeed it was.  Join the Mobile Infantry today ...

Medic!

Good post.  I thought the trick answer was because the Earth is flat or something (Facebook feed seems currently to be inundated by Flerfers who, incidentally, don't like Biden).  Quite refreshing to see some grown up discussion. 

That's "silly" (a technical philosophical term there). By extension... the earth doesn't orbit the sun, rather it orbits some point close to the sun that's the centre of mass of the sun and all it's captive planets/planetoids/asteroids particular noting Jupiter's influence. Ultimately none of the planets (or perhaps only Mercury?) could be said to orbit the sun so your answer is Zero (or maybe 1)

Arguing from utility: that Jupiter doesn't orbit the sun is unhelpful at best, and probably mischievous.

(although I do like a bit of mischievous argument now and again) 

No good social media thread can go for any length of time with reference in some form to Nazis being made.

So I must point out that the real truth that "They" (NASA, CIA, KFC, and others) are trying to keep secret, it that there's a secret Nazi moon base on the dark side of the moon and that Elvis and JFK live there.

No sign of Elvis nor JFK

https://en.wikipedia.org/wiki/Iron_Sky

Of course Jupiter orbits the Sun, by the definition of what an orbit is. It’s a slightly elliptical orbit.

It's all True!

https://www.dailystar.co.uk/news/weird-news/nazi-moon-space-hitler-rocket-1...

And I know for a fact that the RAF modified Lancasters for space travel.  I read it in a newspaper when going on a sunday climbing trip in a club minibus in the 80s

The National Enquirer, and another paper, published photos of WW2 bombers on the moon. A Google search easily finds images of the relevant front pages from those newspapers. Really worth looking up IMO, for a good laugh 

The gullibility of the readers is mind boggling. I used to think the papers published them as a gag/ laugh/ joke, but I no longer think so