# Why are hurricanes structured like galaxies? **URL:** \ **Category:** Factual Questions\ **Created:** [September 8, 2017, 8:54pm UTC](https://boards.straightdope.com/t/why-are-hurricanes-structured-like-galaxies/795840 "2017-09-08T20:54:41Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![pohjonen](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pohjonen/32/423_2.png) [@pohjonen](https://boards.straightdope.com/u/pohjonen)\ **Post date:** [September 8, 2017, 8:54pm UTC](https://boards.straightdope.com/t/why-are-hurricanes-structured-like-galaxies/795840/1 "2017-09-08T20:54:41Z")
With all the pictures of hurricanes taken from space lately, I can’t help but note the similarity between the shapes of hurricanes and galaxies, right down to the wispy arms and centers (black holes, and eyes). I was going to google for the reason, but was unsure how to word it. Can any dopers answer this for me? Thanks. ---
**Author:** ![pohjonen](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pohjonen/32/423_2.png) [@pohjonen](https://boards.straightdope.com/u/pohjonen)\ **Post date:** [September 8, 2017, 8:59pm UTC](https://boards.straightdope.com/t/why-are-hurricanes-structured-like-galaxies/795840/2 "2017-09-08T20:59:23Z")
By the way, I know that all galaxies don’t have that shape. ---
**Author:** ![Grrr](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/grrr/32/146_2.png) [@Grrr](https://boards.straightdope.com/u/Grrr)\ **Post date:** [September 8, 2017, 9:00pm UTC](https://boards.straightdope.com/t/why-are-hurricanes-structured-like-galaxies/795840/3 "2017-09-08T21:00:42Z")
Centripetal force at work. Both entities spin which is going to give similar visual effects. ---
**Author:** ![Procrustus](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/procrustus/32/2994_2.png) [@Procrustus](https://boards.straightdope.com/u/Procrustus)\ **Post date:** [September 8, 2017, 9:01pm UTC](https://boards.straightdope.com/t/why-are-hurricanes-structured-like-galaxies/795840/4 "2017-09-08T21:01:09Z")
I googled your OP title and[got this](http://curious.astro.cornell.edu/about-us/40-our-solar-system/the-earth/climate-and-weather/71-can-any-comparison-be-made-between-spiral-galaxies-and-hurricanes-intermediate) ---
**Author:** ![watchwolf49](https://avatars.discourse-cdn.com/v4/letter/w/e9c0ed/32.png) [@watchwolf49](https://boards.straightdope.com/u/watchwolf49)\ **Post date:** [September 8, 2017, 9:19pm UTC](https://boards.straightdope.com/t/why-are-hurricanes-structured-like-galaxies/795840/5 "2017-09-08T21:19:53Z")
They are both vortices … ---
**Author:** ![John\_Mace](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_mace/32/185_2.png) [@John\_Mace](https://boards.straightdope.com/u/John_Mace)\ **Post date:** [September 8, 2017, 9:28pm UTC](https://boards.straightdope.com/t/why-are-hurricanes-structured-like-galaxies/795840/6 "2017-09-08T21:28:28Z")
> [@Grrr](#): > > Centripetal force at work. Both entities spin which is going to give similar visual effects. The forces at work in Hurricanes are not centripetal, as in a gravitational field. It’s [much more complicated](https://en.wikipedia.org/wiki/Tropical_cyclone#Primary_circulation:_rotating_winds), and relates to the Coriolis effect. ---
**Author:** ![pohjonen](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pohjonen/32/423_2.png) [@pohjonen](https://boards.straightdope.com/u/pohjonen)\ **Post date:** [September 9, 2017, 12:53am UTC](https://boards.straightdope.com/t/why-are-hurricanes-structured-like-galaxies/795840/7 "2017-09-09T00:53:37Z")
> [@watchwolf49](#): > > They are both vortices … This makes sense. Am I correct in understanding that the vortices of hurricanes are caused by temperature variations? ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [September 9, 2017, 1:04am UTC](https://boards.straightdope.com/t/why-are-hurricanes-structured-like-galaxies/795840/8 "2017-09-09T01:04:06Z")
**John Mace** , there are centripetal forces at work in anything that’s moving in a circle. Gravity is one common source of centripetal force, but it’s not the only one. In a hurricane, the centripetal forces come from the pressure difference between the low-pressure center and the high-pressure outside. And to the OP, while all or almost all galaxies have a supermassive black hole in the center, it won’t show up in a picture of the whole galaxy, the way a hurricane’s eye would. The central black hole, or even its accretion disk, is far, far smaller than the galaxy as a whole. ---
**Author:** ![Saint\_Cad](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/saint_cad/32/18907_2.png) [@Saint\_Cad](https://boards.straightdope.com/u/Saint_Cad)\ **Post date:** [September 9, 2017, 1:13am UTC](https://boards.straightdope.com/t/why-are-hurricanes-structured-like-galaxies/795840/9 "2017-09-09T01:13:10Z")
> [@Grrr](#): > > Centripetal force at work. Both entities spin which is going to give similar visual effects. Are you sure? I would think it is conservation of angular momentum. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [September 9, 2017, 1:23am UTC](https://boards.straightdope.com/t/why-are-hurricanes-structured-like-galaxies/795840/10 "2017-09-09T01:23:10Z")
Centripetal force and angular momentum are two concepts which can’t really be disentangled from each other, since they’ll both show up every time you have rotation. ---
**Author:** ![watchwolf49](https://avatars.discourse-cdn.com/v4/letter/w/e9c0ed/32.png) [@watchwolf49](https://boards.straightdope.com/u/watchwolf49)\ **Post date:** [September 9, 2017, 5:14am UTC](https://boards.straightdope.com/t/why-are-hurricanes-structured-like-galaxies/795840/11 "2017-09-09T05:14:34Z")
**Chronos** is correct, the word “centripetal” only defines the direction of the force, towards the center … in a galaxy, this centripetal force is caused by gravity; in a hurricane this centripetal force is caused by the pressure force; so both are correct usages … We have to be very careful applying the conservation of angular momentum to a hurricane or any cyclone … these particular vortices are under torque, so angular momentum is increasing until they reach their frictional limits … one thing a galaxy doesn’t do is precipitate water vapor so this can’t be relied upon to explain torque there, not sure we can say galaxies are even under torque … but either way, they can both be explained as vortices and all the vortex equations will hold true … No one knows why an eye forms at the center of a hurricane, so we don’t know why galaxies don’t have eyes … research continues … ---
**Author:** ![watchwolf49](https://avatars.discourse-cdn.com/v4/letter/w/e9c0ed/32.png) [@watchwolf49](https://boards.straightdope.com/u/watchwolf49)\ **Post date:** [September 9, 2017, 5:20am UTC](https://boards.straightdope.com/t/why-are-hurricanes-structured-like-galaxies/795840/12 "2017-09-09T05:20:54Z")
> [@pohjonen](#): > > This makes sense. Am I correct in understanding that the vortices of hurricanes are caused by temperature variations? Pressure variations, which could be in turn caused by temperature variations, but there are other mechanics that can cause these initiating pressure variations … once the initial vortex is formed and water starts condensing, then it’s just balls out torque that drives the hurricane … ---
**Author:** ![Beckdawrek](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beckdawrek/32/3647_2.png) [@Beckdawrek](https://boards.straightdope.com/u/Beckdawrek)\ **Post date:** [September 9, 2017, 5:24am UTC](https://boards.straightdope.com/t/why-are-hurricanes-structured-like-galaxies/795840/13 "2017-09-09T05:24:21Z")
The swirl shape is a constant in nature…i learned that in art school…not science-y…i know…forgive me ---
**Author:** ![watchwolf49](https://avatars.discourse-cdn.com/v4/letter/w/e9c0ed/32.png) [@watchwolf49](https://boards.straightdope.com/u/watchwolf49)\ **Post date:** [September 9, 2017, 5:29am UTC](https://boards.straightdope.com/t/why-are-hurricanes-structured-like-galaxies/795840/14 "2017-09-09T05:29:22Z")
Thank you **Beckdawrek** … sometimes we delve too deep into the science of nature we sometimes forget just how beautiful these things are … ---
**Author:** ![Beckdawrek](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beckdawrek/32/3647_2.png) [@Beckdawrek](https://boards.straightdope.com/u/Beckdawrek)\ **Post date:** [September 10, 2017, 12:03am UTC](https://boards.straightdope.com/t/why-are-hurricanes-structured-like-galaxies/795840/15 "2017-09-10T00:03:00Z")
You’re welcome ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [September 10, 2017, 12:21pm UTC](https://boards.straightdope.com/t/why-are-hurricanes-structured-like-galaxies/795840/16 "2017-09-10T12:21:51Z")
Apparently, you’re not the only one who’s noticed this, as evidenced by [today’s _Schlock Mercenary_](http://www.schlockmercenary.com/2017-09-10). ---
**Author:** ![Isilder](https://avatars.discourse-cdn.com/v4/letter/i/cc9497/32.png) [@Isilder](https://boards.straightdope.com/u/Isilder)\ **Post date:** [September 10, 2017, 1:42pm UTC](https://boards.straightdope.com/t/why-are-hurricanes-structured-like-galaxies/795840/17 "2017-09-10T13:42:35Z")
> [@Chronos](#): > > Centripetal force and angular momentum are two concepts which can’t really be disentangled from each other, since they’ll both show up every time you have rotation. worse, “momentum” has no physical manifestation. Its a 4th rule to help apply Newston’s 3… basically momentum is a corollary of Newton’s law “every action has equal and opposite” , its listed as different because its extended to apply over definite time frames… The momentum must be conserved , or the change must be due to external influences. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [September 10, 2017, 10:01pm UTC](https://boards.straightdope.com/t/why-are-hurricanes-structured-like-galaxies/795840/18 "2017-09-10T22:01:29Z")
Beg pardon? Of course momentum (linear and angular) has a physical manifestation. In what sense doesn’t it? ---
**Author:** ![Irishman](https://avatars.discourse-cdn.com/v4/letter/i/b487fb/32.png) [@Irishman](https://boards.straightdope.com/u/Irishman)\ **Post date:** [September 11, 2017, 9:38pm UTC](https://boards.straightdope.com/t/why-are-hurricanes-structured-like-galaxies/795840/19 "2017-09-11T21:38:55Z")
Momentum is the manifestation of the first two of Newton’s Laws. An object in motion tends to stay in motion. –\> Momentum An object at rest tends to stay at rest. –\> Momentum For every action, there is an equal and opposite reaction. –\> Forces apply both directions: on this from that and from this on that. F= m a is really a [simplification](https://en.wikipedia.org/wiki/Momentum#Objects_of_variable_mass) for constant mass. With variable mass, mass changes with time, such that If P(t) = momentum = m(t) v(t), then F = m(t) dv/dt - u dm/dt Where u = the velocity of the ejected/accreted mass _as seen in the object’s rest frame,_ also called the ejection velocity. ---
**Author:** ![watchwolf49](https://avatars.discourse-cdn.com/v4/letter/w/e9c0ed/32.png) [@watchwolf49](https://boards.straightdope.com/u/watchwolf49)\ **Post date:** [September 11, 2017, 9:52pm UTC](https://boards.straightdope.com/t/why-are-hurricanes-structured-like-galaxies/795840/20 "2017-09-11T21:52:11Z")
Kitchen counter science: Cupboard door of mass _m_ traveling at velocity _v_ has enough momentum _p_ to create bruise diameter _d[sub]ouch[/sub]_ on forehead … [Next page](https://boards.straightdope.com/t/why-are-hurricanes-structured-like-galaxies/795840.md?page=2)