# What gravitational force is stronger, the star Alpha Centuri far away or a skyscraper next to you? **URL:** \ **Category:** Factual Questions\ **Created:** [October 15, 2020, 2:21pm UTC](https://boards.straightdope.com/t/what-gravitational-force-is-stronger-the-star-alpha-centuri-far-away-or-a-skyscraper-next-to-you/923013 "2020-10-15T14:21:16Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![jonpluc](https://avatars.discourse-cdn.com/v4/letter/j/fbc32d/32.png) [@jonpluc](https://boards.straightdope.com/u/jonpluc)\ **Post date:** [October 15, 2020, 2:21pm UTC](https://boards.straightdope.com/t/what-gravitational-force-is-stronger-the-star-alpha-centuri-far-away-or-a-skyscraper-next-to-you/923013/1 "2020-10-15T14:21:16Z")
I was having a conversation about the sillyness of astrology, and the (of course a girl) was trying to tell me that the stars have gravity that effect the tides and can affect your personality in the same way. I argued that because the stars are so far away, thier gravity effects are essentially zero and i argued that the gravitational effects of a skyscraper (mass=gravity) that you brush your shoulder with as you walk by on the street probably has a greater gravitational impact on you. I of course have no idea if this is actually true. Is it? ---
**Author:** ![Andy\_L](https://avatars.discourse-cdn.com/v4/letter/a/c67d28/32.png) [@Andy\_L](https://boards.straightdope.com/u/Andy_L)\ **Post date:** [October 15, 2020, 2:27pm UTC](https://boards.straightdope.com/t/what-gravitational-force-is-stronger-the-star-alpha-centuri-far-away-or-a-skyscraper-next-to-you/923013/2 "2020-10-15T14:27:59Z")
You’re absolutely right - both times. The gravitational effect of Alpha C on you is way smaller than the effect due to the skyscraper - and the tidal effect of Alpha C is even smaller than the tidal effect of the skyscraper (tides decrease with the third power of the distance). ---
**Author:** ![Elmer\_J.Fudd](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/elmer_j.fudd/32/1211_2.png) [@Elmer\_J.Fudd](https://boards.straightdope.com/u/Elmer_J.Fudd)\ **Post date:** [October 15, 2020, 2:34pm UTC](https://boards.straightdope.com/t/what-gravitational-force-is-stronger-the-star-alpha-centuri-far-away-or-a-skyscraper-next-to-you/923013/3 "2020-10-15T14:34:05Z")
How about a cow in the next county? From [Gravitational attraction of stars and cows](https://www.johndcook.com/blog/2018/03/28/cow-astrology/) Alpha Centauri, the closest star to Earth (other than the sun, of course) has about the same pull as a cow 18 miles away. ---
**Author:** ![Colibri](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/colibri/32/1841_2.png) [@Colibri](https://boards.straightdope.com/u/Colibri)\ **Post date:** [October 15, 2020, 4:48pm UTC](https://boards.straightdope.com/t/what-gravitational-force-is-stronger-the-star-alpha-centuri-far-away-or-a-skyscraper-next-to-you/923013/4 "2020-10-15T16:48:37Z")
> [@jonpluc](#): > > (of course a girl) **Moderator Note** **jonpluc** , let’s refrain from sexist remarks in this forum (or elsewhere on the board). This implies that silly remarks are typical of “girls.” No warning issued, but don’t do this in the future. Colibri General Questions Moderator ---
**Author:** ![Keeve](https://avatars.discourse-cdn.com/v4/letter/k/f07891/32.png) [@Keeve](https://boards.straightdope.com/u/Keeve)\ **Post date:** [October 15, 2020, 5:21pm UTC](https://boards.straightdope.com/t/what-gravitational-force-is-stronger-the-star-alpha-centuri-far-away-or-a-skyscraper-next-to-you/923013/5 "2020-10-15T17:21:26Z")
> [@Elmer\_J.Fudd](#): > > Alpha Centauri, the closest star to Earth (other than the sun, of course) has about the same pull as a cow 18 miles away. But the skyscraper is both more massive and much closer than that cow. It should be pretty easy to get a wild guess about the mass and distance of the skyscraper and of Alpha Centauri, but I don’t remember the formula for gravitational attraction. Anyone else? ---
**Author:** ![Northern\_Piper](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/northern_piper/32/5304_2.png) [@Northern\_Piper](https://boards.straightdope.com/u/Northern_Piper)\ **Post date:** [October 15, 2020, 5:34pm UTC](https://boards.straightdope.com/t/what-gravitational-force-is-stronger-the-star-alpha-centuri-far-away-or-a-skyscraper-next-to-you/923013/6 "2020-10-15T17:34:23Z")
I can’t do formulas on my phone, but it’s given in the wiki article: > **[Newton's law of universal gravitation](https://en.wikipedia.org/wiki/Newton%27s_law_of_universal_gravitation)** > > Pages for logged out editors learn more > > Newton's law of universal gravitation is usually stated as that every particle attracts every other particle in the universe with a force that is proportional to the product of their masses and inversely proportional to the square of the distance between their centers.\[note 1\] The publication of the law has become known as the "first great unification", as it marked the unification of the previously described phenomena of gravity on Earth with kno... ---
**Author:** ![Chingon](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chingon/32/17645_2.png) [@Chingon](https://boards.straightdope.com/u/Chingon)\ **Post date:** [October 15, 2020, 5:39pm UTC](https://boards.straightdope.com/t/what-gravitational-force-is-stronger-the-star-alpha-centuri-far-away-or-a-skyscraper-next-to-you/923013/7 "2020-10-15T17:39:21Z")
The ratio of forces would be: (mass\_object1/mass\_object2)/(distance\_object1/distance\_object2)^2 so in this case the mass of Alpha Centuri is about 22 orders of magnitude larger. If we imagine you’re standing 1 m away from the skyscraper them the distance to Alpha Centuri is 16 orders of magnitude larger, so we get: 10^22/(10^16)^2 which is about 10^-10 pretty small. ---
**Author:** ![Andy\_L](https://avatars.discourse-cdn.com/v4/letter/a/c67d28/32.png) [@Andy\_L](https://boards.straightdope.com/u/Andy_L)\ **Post date:** [October 15, 2020, 5:41pm UTC](https://boards.straightdope.com/t/what-gravitational-force-is-stronger-the-star-alpha-centuri-far-away-or-a-skyscraper-next-to-you/923013/8 "2020-10-15T17:41:56Z")
mass divided by distance squared for gravity (times a constant we don’t need for this comparison) mass divided by distance cubed for tides (times the same constant). The distance to Alpha C is 10^17 feet (or so). The mass of Alpha C is 2.5_10^29 kg. So the force from Alpha C is 2.5_10^29/10^34 = 2.5/10^5. The skyscraper is (say) 100 feet way, so its force is Mass of Skyscraper/10^4. If the skyscraper weighs more than a quarter of a kilogram (half a pound) - **which it does,** the skyscraper has a larger force than the star. ---
**Author:** ![Chingon](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chingon/32/17645_2.png) [@Chingon](https://boards.straightdope.com/u/Chingon)\ **Post date:** [October 15, 2020, 5:53pm UTC](https://boards.straightdope.com/t/what-gravitational-force-is-stronger-the-star-alpha-centuri-far-away-or-a-skyscraper-next-to-you/923013/9 "2020-10-15T17:53:44Z")
On the other hand, if the skyscraper was about 100km away the gravitational force would be about equal to Alpha Centauri. ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [October 15, 2020, 6:00pm UTC](https://boards.straightdope.com/t/what-gravitational-force-is-stronger-the-star-alpha-centuri-far-away-or-a-skyscraper-next-to-you/923013/10 "2020-10-15T18:00:42Z")
The bottom line of course is that it doesn’t matter which skyscrapers, cows, cars, whatever are nearby. Whatever random arrangement of terrestrial stuff there is, and wherever on Earth you happen to stand, the effects of all the Earthly stuff totally overwhelms the microscopic gravitational signal from the planets, much less the far more distant stars. ---
**Author:** ![Elmer\_J.Fudd](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/elmer_j.fudd/32/1211_2.png) [@Elmer\_J.Fudd](https://boards.straightdope.com/u/Elmer_J.Fudd)\ **Post date:** [October 15, 2020, 6:25pm UTC](https://boards.straightdope.com/t/what-gravitational-force-is-stronger-the-star-alpha-centuri-far-away-or-a-skyscraper-next-to-you/923013/11 "2020-10-15T18:25:53Z")
The formula is on the link I posted. The board wouldn’t let me C&P it. ---
**Author:** ![Yllaria](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/yllaria/32/3452_2.png) [@Yllaria](https://boards.straightdope.com/u/Yllaria)\ **Post date:** [October 15, 2020, 6:27pm UTC](https://boards.straightdope.com/t/what-gravitational-force-is-stronger-the-star-alpha-centuri-far-away-or-a-skyscraper-next-to-you/923013/12 "2020-10-15T18:27:18Z")
Not to mention the gravitational pull of the Earth. That’s got to swamp out everything else. Who was it who said that at the time of a baby’s birth, the gravitational effect of the obstetrician is larger than the gravitational effect of any planet. (The arrangement of the planets against the fixed stars is used in calculating natal charts. Most astrology fans cite the gravitational pull of the planets, rather than the stars.) ---
**Author:** ![Munch](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/munch/32/5281_2.png) [@Munch](https://boards.straightdope.com/u/Munch)\ **Post date:** [October 15, 2020, 6:28pm UTC](https://boards.straightdope.com/t/what-gravitational-force-is-stronger-the-star-alpha-centuri-far-away-or-a-skyscraper-next-to-you/923013/13 "2020-10-15T18:28:57Z")
> [@Yllaria](#): > > Who was it who said that at the time of a baby’s birth, the gravitational effect of the obstetrician is larger than the gravitational effect of any planet. We did that calculation high school - and you could add up ALL the exterior planets as if it were a full alignment, and it wouldn’t cancel out a decent-sized OB. ---
**Author:** ![Tierce](https://avatars.discourse-cdn.com/v4/letter/t/ea5d25/32.png) [@Tierce](https://boards.straightdope.com/u/Tierce)\ **Post date:** [October 15, 2020, 6:33pm UTC](https://boards.straightdope.com/t/what-gravitational-force-is-stronger-the-star-alpha-centuri-far-away-or-a-skyscraper-next-to-you/923013/14 "2020-10-15T18:33:54Z")
> [@Yllaria](#): > > Who was it who said that at the time of a baby’s birth, the gravitational effect of the obstetrician is larger than the gravitational effect of any planet. Carl Sagan in the original _Cosmos_ series. ---
**Author:** ![Yllaria](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/yllaria/32/3452_2.png) [@Yllaria](https://boards.straightdope.com/u/Yllaria)\ **Post date:** [October 15, 2020, 6:35pm UTC](https://boards.straightdope.com/t/what-gravitational-force-is-stronger-the-star-alpha-centuri-far-away-or-a-skyscraper-next-to-you/923013/15 "2020-10-15T18:35:23Z")
> [@Tierce](#): > > Carl Sagan in the original _Cosmos_ series. Thanks. I was too lazy to google. ---
**Author:** ![TriPolar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripolar/32/3008_2.png) [@TriPolar](https://boards.straightdope.com/u/TriPolar)\ **Post date:** [October 15, 2020, 6:39pm UTC](https://boards.straightdope.com/t/what-gravitational-force-is-stronger-the-star-alpha-centuri-far-away-or-a-skyscraper-next-to-you/923013/16 "2020-10-15T18:39:48Z")
> [@Yllaria](#): > > Who was it who said that at the time of a baby’s birth, the gravitational effect of the obstetrician is larger than the gravitational effect of any planet in Homeopathic Astrology the weaker the gravitational effect of a planet the more effect it has on a person’s life. It’s the memory of the gravity that makes the difference. ---
**Author:** ![Yllaria](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/yllaria/32/3452_2.png) [@Yllaria](https://boards.straightdope.com/u/Yllaria)\ **Post date:** [October 15, 2020, 6:43pm UTC](https://boards.straightdope.com/t/what-gravitational-force-is-stronger-the-star-alpha-centuri-far-away-or-a-skyscraper-next-to-you/923013/17 "2020-10-15T18:43:01Z")
> [@TriPolar](#): > > in Homeopathic Astrology the weaker the gravitational effect of a planet the more effect it has on a person’s life. It’s the memory of the gravity that makes the difference. But . . . but . . that means that we’re most strongly affected by stars we can’t see. ---
**Author:** ![D18](https://avatars.discourse-cdn.com/v4/letter/d/c57346/32.png) [@D18](https://boards.straightdope.com/u/D18)\ **Post date:** [October 15, 2020, 7:11pm UTC](https://boards.straightdope.com/t/what-gravitational-force-is-stronger-the-star-alpha-centuri-far-away-or-a-skyscraper-next-to-you/923013/18 "2020-10-15T19:11:53Z")
I learned about the [https://en.wikipedia.org/wiki/Schiehallion\_experiment](https://en.wikipedia.org/wiki/Schiehallion_experiment) Schiehallion Experiment here on the Dope - the gravitational effect of a mountain is measurable with low-tech tools! ---
**Author:** ![bump](https://avatars.discourse-cdn.com/v4/letter/b/7c8e57/32.png) [@bump](https://boards.straightdope.com/u/bump)\ **Post date:** [October 15, 2020, 7:13pm UTC](https://boards.straightdope.com/t/what-gravitational-force-is-stronger-the-star-alpha-centuri-far-away-or-a-skyscraper-next-to-you/923013/19 "2020-10-15T19:13:29Z")
That was what I was thinking- Newton figured out how to calculate this a long time ago. ---
**Author:** ![Riemann](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/riemann/32/3133_2.png) [@Riemann](https://boards.straightdope.com/u/Riemann)\ **Post date:** [October 15, 2020, 8:16pm UTC](https://boards.straightdope.com/t/what-gravitational-force-is-stronger-the-star-alpha-centuri-far-away-or-a-skyscraper-next-to-you/923013/20 "2020-10-15T20:16:01Z")
> [@Yllaria](#): > > the gravitational effect of the obstetrician Is this how gravitational dilation works? [Next page](https://boards.straightdope.com/t/what-gravitational-force-is-stronger-the-star-alpha-centuri-far-away-or-a-skyscraper-next-to-you/923013.md?page=2)