# Does a full moon cause a higher tide than usual? **URL:** \ **Category:** Factual Questions\ **Created:** [May 8, 2001, 1:35am UTC](https://boards.straightdope.com/t/does-a-full-moon-cause-a-higher-tide-than-usual/64708 "2001-05-08T01:35:17Z")\ **Posts on this page:** 11\ **Page:** 1
**Author:** ![guitarmax\_99](https://avatars.discourse-cdn.com/v4/letter/g/f19dbf/32.png) [@guitarmax\_99](https://boards.straightdope.com/u/guitarmax_99)\ **Post date:** [May 8, 2001, 1:35am UTC](https://boards.straightdope.com/t/does-a-full-moon-cause-a-higher-tide-than-usual/64708/1 "2001-05-08T01:35:17Z")
Was talking to a friend who is convinced that tides are higher on the full moon than on the other days of the month. If this is true, then why? ---
**Author:** ![Cabbage](https://avatars.discourse-cdn.com/v4/letter/c/f07891/32.png) [@Cabbage](https://boards.straightdope.com/u/Cabbage)\ **Post date:** [May 8, 2001, 2:11am UTC](https://boards.straightdope.com/t/does-a-full-moon-cause-a-higher-tide-than-usual/64708/2 "2001-05-08T02:11:22Z")
When the moon is full or new, its tidal pull on the earth lines up with the sun’s pull, so you do get a higher tide then (spring tide). Similarly, when the sun and moon are at “right angles” to each other (first and last quarter moons), you get lower high tides than usual (neap tide), since the sun and moon are working against each other. Here’s a little animation to show it: [http://www.sfgate.com/getoutside/1996/jun/tides.html](http://www.sfgate.com/getoutside/1996/jun/tides.html) ---
**Author:** ![choosybeggar](https://avatars.discourse-cdn.com/v4/letter/c/8c91f0/32.png) [@choosybeggar](https://boards.straightdope.com/u/choosybeggar)\ **Post date:** [May 8, 2001, 5:13am UTC](https://boards.straightdope.com/t/does-a-full-moon-cause-a-higher-tide-than-usual/64708/3 "2001-05-08T05:13:04Z")
How can that make sense? Full moons occur every 28 days or so, whereas Spring tides occur (going out on a limb here) only once per year. **Chronos,** where are you when we need you? PS did you see my response to you in [this thread?](http://boards.straightdope.com/sdmb/showthread.php?threadid=69293) ---
**Author:** ![hawthorne](https://avatars.discourse-cdn.com/v4/letter/h/c89c15/32.png) [@hawthorne](https://boards.straightdope.com/u/hawthorne)\ **Post date:** [May 8, 2001, 5:57am UTC](https://boards.straightdope.com/t/does-a-full-moon-cause-a-higher-tide-than-usual/64708/4 "2001-05-08T05:57:35Z")
from Cabbage’s link > [@](#): > > […] causing very high and very low tides which are called spring tides, though they have nothing to do with the season. ---
**Author:** ![gryphil](https://avatars.discourse-cdn.com/v4/letter/g/e68b1a/32.png) [@gryphil](https://boards.straightdope.com/u/gryphil)\ **Post date:** [May 8, 2001, 6:53am UTC](https://boards.straightdope.com/t/does-a-full-moon-cause-a-higher-tide-than-usual/64708/5 "2001-05-08T06:53:04Z")
Is there any discernable difference between the new moon spring tide and the full moon spring tide? ---
**Author:** ![Badtz\_Maru](https://avatars.discourse-cdn.com/v4/letter/b/e36b37/32.png) [@Badtz\_Maru](https://boards.straightdope.com/u/Badtz_Maru)\ **Post date:** [May 8, 2001, 10:20am UTC](https://boards.straightdope.com/t/does-a-full-moon-cause-a-higher-tide-than-usual/64708/6 "2001-05-08T10:20:09Z")
> [@](#): > > \*Originally posted by gryphil \* > \*\*Is there any discernable difference between the new moon spring tide and the full moon spring tide? > \*\* I wouldn’t think so. ---
**Author:** ![AWB](https://avatars.discourse-cdn.com/v4/letter/a/bb73d2/32.png) [@AWB](https://boards.straightdope.com/u/AWB)\ **Post date:** [May 8, 2001, 12:36pm UTC](https://boards.straightdope.com/t/does-a-full-moon-cause-a-higher-tide-than-usual/64708/7 "2001-05-08T12:36:29Z")
> [@](#): > > \*Originally posted by choosybeggar \* > \*\*How can that make sense? > > Full moons occur every 28 days or so, whereas Spring tides occur (going out on a limb here) only once per year. > \*\* The term spring here does not relate to the season, but more to another definition “leap, jump, or bound”. They do indeed occur at new and full moons, about twice a month. And because the high tides are higher, the low tides are lower during new and full moons. ---
**Author:** ![choosybeggar](https://avatars.discourse-cdn.com/v4/letter/c/8c91f0/32.png) [@choosybeggar](https://boards.straightdope.com/u/choosybeggar)\ **Post date:** [May 8, 2001, 2:09pm UTC](https://boards.straightdope.com/t/does-a-full-moon-cause-a-higher-tide-than-usual/64708/8 "2001-05-08T14:09:30Z")
> [@](#): > > \*Originally posted by choosybeggar \* > \*\*How can that make sense? > > Full moons occur every 28 days or so, whereas Spring tides occur (going out on a limb here) only once per year. > > \*\* Thank the good lord for disclaimers. [sub]You still look like an idiot anyway **choosybeggar** [/sub] ---
**Author:** ![The\_Bad\_Astronomer](https://avatars.discourse-cdn.com/v4/letter/t/f05b48/32.png) [@The\_Bad\_Astronomer](https://boards.straightdope.com/u/The_Bad_Astronomer)\ **Post date:** [May 8, 2001, 8:52pm UTC](https://boards.straightdope.com/t/does-a-full-moon-cause-a-higher-tide-than-usual/64708/9 "2001-05-08T20:52:55Z")
First the animation linked above is misleading. A line drawn through the high tides bulges points more or less at the Moon (actually, a little bit ahead of the Moon’s motion). This animation implies we only get high tides when the Sun and Moon align. The Moon’s tidal force on the Earth is roughly twice the Sun’s. So even at first and third quarter Moon we still get noticeable high tides. The tidal height also depends on the Moon’s distance, though the total effect is rather weak. If you get a new or full Moon when it’s closest to the Earth, _and also around January 4_ when the Earth is closest to the Sun, you get the maximum potential high tide. The actual tide height depends on currents, coastline shape, winds, what have you. Your kilometerage may very. –The Bad Astronomer, who just wrote a 4000 word chapter about tides for a book ---
**Author:** ![casdave](https://avatars.discourse-cdn.com/v4/letter/c/c6cbf5/32.png) [@casdave](https://boards.straightdope.com/u/casdave)\ **Post date:** [May 8, 2001, 9:53pm UTC](https://boards.straightdope.com/t/does-a-full-moon-cause-a-higher-tide-than-usual/64708/10 "2001-05-08T21:53:54Z")
IIRC one of the high tides occurs when the sun and moon are at opposite sides as well as when they are aligned. If the moon is at one side of the earth a corresponding tidal bulge occurs exactly at the other side, and if the sun is at that side the effect is enhanced ---
**Author:** ![CurtC](https://avatars.discourse-cdn.com/v4/letter/c/ce73a5/32.png) [@CurtC](https://boards.straightdope.com/u/CurtC)\ **Post date:** [May 9, 2001, 4:44am UTC](https://boards.straightdope.com/t/does-a-full-moon-cause-a-higher-tide-than-usual/64708/11 "2001-05-09T04:44:23Z")
Not only is that site’s animation misleading, its description of what causes tides is completely wrong. They say: > [@](#): > > The moon has a gravitational pull on this layer of water as it orbits the earth. This pull causes the water to bulge toward the moon. Because the earth is spinning there will be a bulge on the opposite side of the earth as well. Now this page was last updated in 1996, so maybe the state of tidal knowledge was not so advanced then. To clarify, the bulges on opposite sides are due to the fact that the sides of the Earth nearest to and farthest from the Moon have higher and lower (respectively) gravitational tugs towards it. This causes the whole Earth to try to assume an ellipsoid shape, with bulges to and from the Moon. The water is the easiest to deform into that shape, so it does most of the moving. However, the solid parts of the Earth also move some.