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Is the solar system a helix or what?

January 17, 2015


Sort of. Bits of it…?

Although, my little monkey-man brain thought not at first.

Sort of.

First things first. I imagine everyone on the internet has seen this:

or its predecessors (or its gif versions) at least 42 times in the last couple of years. Very popular and very pretty it is too.

As the creator says it’s not to scale, for various sensible reasons, but is it accurate?

I’m no Star-doctor so I did a bit of delving around the internet and ploughing through various comment sections it became apparent that some people say Yes! and some say No! and some say Welllll, yes and no.

At first I thought it can’t be accurate as the sun takes 250,000,000 years (depending on which estimate you want to use) to orbit the galactic centre and my little brain tried to imagine 250 million little squiggles around the edges of one of those 360° protractors you had at school.

Surely this would make a solid cylinder, not a long wavy helix, if you animated it? I imagined a super squished slinky toy.

Like the two ends here rather than the middle.

I thought I would soon prove myself right, and the silly animating man (or woman) wrong, by doing some maths and stuff.

Liking the slinky idea, I first imagined the earth to have a diameter of one millimetre.

This would make the sun 10.9 cm in diameter.

They would be 11.929 metres apart (on average, as the earth’s orbit is slightly squished).

So far so good: I can imagine a grapefruit being orbited by a broken pencil nib about five and a half me-heights away from each other. (At a 60° angle to the galactic plane).

Next up is a bit more difficult (I think I’ve done the maths right but it made my brain hurt a bit)

Galactic centre would be about 19,527,559 km away from our grapefruit and slinky/pencil nib combo.

This means we would have to walk in a circle 122,600,000 km long.

Every 488 metres that we walk, our 1mm wide slinky wire will complete one orbit around us. (Actually we’ll have to fly otherwise we’ll scuff the grass up a bit.)

Holding the grapefruit, and a ten metre stick with our 1mm earth on the end, we will have to walk at 711,000 km/h. (Hmm, we might run out of grass here).

It will take just over a week to complete the full circle around galactic centre*.

I think.

So, anyway I was wrong to imagine the super condensed slinky forming an elliptical tube around galactic centre. It would indeed be a helix, although a verrrry long one.

I can see about sixty coils in that slinky above. You’ll have to stretch it out 29km end to end.

Space is weird

and big.

So the animator is right about the helix thing but:

Once again, I am not a space-science man but it seems to me that on the video he (or she) has also confused the earth’s axial precession (26,000 years) with the amount of time it takes to cross the galactic plane (about 30,000,000 years).

By my calcliations our grapefruit will have to cross the galactic plane about 8 times a week (or eight times every 250,000,000 years in the real universe).

On top of that, I have no idea how he makes the sun itself move in a helix. How does it get attracted towards galactic centre and then pushed out again? Up and down is fine (relative to galactic plane of course)

Is he trolling?

Either that or she knows something I don’t.

(Or he’s made a genuine mistake I suppose)

Please, send any corrections or head-massage devices to the usual address…

Measurements wot I used:

Diameter of Earth: 12,742 km

Earth to sun: 152,000,000 km

Sun is 109 times bigger than earth.

Sun to galactic centre: 8000 parsecs

One parsec is about 31 trillion km


Estimates of the length of time for the Solar System to orbit once around the center of the Milky Way Galaxy range from 225 to 250 million terrestrial years. I went for 250 million.

*So the first dinosaurs were in about the same position as we are now (relative to GC)


From → Astronomy

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