# Moon Mirage **URL:** \ **Category:** Factual Questions\ **Created:** [January 1, 2003, 11:44pm UTC](https://boards.straightdope.com/t/moon-mirage/146111 "2003-01-01T23:44:58Z")\ **Posts on this page:** 10\ **Page:** 1
**Author:** ![jclune](https://avatars.discourse-cdn.com/v4/letter/j/9dc877/32.png) [@jclune](https://boards.straightdope.com/u/jclune)\ **Post date:** [January 1, 2003, 11:44pm UTC](https://boards.straightdope.com/t/moon-mirage/146111/1 "2003-01-01T23:44:58Z")
I know why the moon seems larger at the horizon. But why does that large moon seem wider horizontally than vertically? In other words, why does it seem more like an egg than a cirlce? ---
**Author:** ![Jinx](https://avatars.discourse-cdn.com/v4/letter/j/c6cbf5/32.png) [@Jinx](https://boards.straightdope.com/u/Jinx)\ **Post date:** [January 1, 2003, 11:58pm UTC](https://boards.straightdope.com/t/moon-mirage/146111/2 "2003-01-01T23:58:07Z")
Do you see this during a gibbous phase? And, even during a full moon phase? I WAG you’re seeing a gibbous moon especially a waning gibbous moon. Can you clarify/quantify conditions when you think you observe this? - Jinx ---
**Author:** ![jclune](https://avatars.discourse-cdn.com/v4/letter/j/9dc877/32.png) [@jclune](https://boards.straightdope.com/u/jclune)\ **Post date:** [January 2, 2003, 1:33am UTC](https://boards.straightdope.com/t/moon-mirage/146111/3 "2003-01-02T01:33:44Z")
It might simplify things to speak of the sun, for the effect occurs there as well. For both full moons and the sun at sunset and sunrise, the body seems wider than taller (which is not the case while it is higher in the sky, where it appears circular). Does that help clarify? ---
**Author:** ![sailor](https://avatars.discourse-cdn.com/v4/letter/s/a587f6/32.png) [@sailor](https://boards.straightdope.com/u/sailor)\ **Post date:** [January 2, 2003, 1:42am UTC](https://boards.straightdope.com/t/moon-mirage/146111/4 "2003-01-02T01:42:32Z")
Atmospheric refraction which is very marked at such low altitude. In fact, You are seeing the edge or limb after it is geometrically below the horizon. ---
**Author:** ![Snickers](https://avatars.discourse-cdn.com/v4/letter/s/5daacb/32.png) [@Snickers](https://boards.straightdope.com/u/Snickers)\ **Post date:** [January 2, 2003, 2:46pm UTC](https://boards.straightdope.com/t/moon-mirage/146111/5 "2003-01-02T14:46:17Z")
**Sailor’s** got it right. In greater detail… When you look at the moon (or sun) at the horizon, you’re looking through a greater amount of Earth’s atmosphere than when you look, say, straight up. This greater amount of atmosphere can act as a lens, bending the light of the objects. At the horizon, the effect of the atmospheric lens is to bend the light from the moon or sun, flattening them and distorting their shape. You’ll always see egg-shaped moons and suns near the horizon at sunrise and sunset. As the moon or sun rises, you’re looking through less and less atmosphere to distort the image, and their shape appears more spherical. Thank you - I’m here all week. Remember to tip your waitresses! Snicks ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [January 2, 2003, 2:52pm UTC](https://boards.straightdope.com/t/moon-mirage/146111/6 "2003-01-02T14:52:23Z")
When the moon or sun is near the horizon, we are often therefore seeing it against the context of distant objects, which appear small. I’d be surprised if there’s very much measurable difference in the size of the moon at any position; you could test it by holding a pair of calipers at arm’s length and measuring the apparent size of the moon near the horizon and again when it is high in the sky; my guess is that there will be little measurable difference - it’s mostly perceptual. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [January 2, 2003, 2:59pm UTC](https://boards.straightdope.com/t/moon-mirage/146111/7 "2003-01-02T14:59:50Z")
Gaaah! ignore everything I just posted; I’ll just read the question properly next time. ---
**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:** [January 2, 2003, 10:29pm UTC](https://boards.straightdope.com/t/moon-mirage/146111/8 "2003-01-02T22:29:30Z")
I wrote an essay about this on my website [in the Bitsesize section](http://www.badastronomy.com/bitesize/sunbend.html). There are links to other pages as well. ---
**Author:** ![jclune](https://avatars.discourse-cdn.com/v4/letter/j/9dc877/32.png) [@jclune](https://boards.straightdope.com/u/jclune)\ **Post date:** [January 7, 2003, 5:09am UTC](https://boards.straightdope.com/t/moon-mirage/146111/9 "2003-01-07T05:09:55Z")
I checked out the link to the paper that was posted, and found this as the core of the explanation: > [@](#): > > Just at sunset (or sunrise), the top of the Sun is farther from the horizon than the bottom. The bottom part is going through more air, and is bent more! The light from the bottom gets bent up, towards the top, which makes the Sun look squashed. I am still confused. What is the effect of the bending of the light? You mention the effect is more pronounced at the bottom during sunset…the implication being that the effect would be less pronounced at the top. The result, one would think, would be a tapering off of the illusion (a pyramid if the effect stretches the light, an inverse pyramid if it narrows it). Why does the effect work similarly on the top and bottom, leaving the center alone (or, conversly, why does it work on the center and not on the top or bottom)? Why is the stretching only horizontal and not vertical? PS. The article you posted mentioned the refracting of blue light. I have an interesting question that springs from that topic but will ask it in a new thread. Please check it out. Thanks for all your input. Jeff ---
**Author:** ![sailor](https://avatars.discourse-cdn.com/v4/letter/s/a587f6/32.png) [@sailor](https://boards.straightdope.com/u/sailor)\ **Post date:** [January 7, 2003, 2:30pm UTC](https://boards.straightdope.com/t/moon-mirage/146111/10 "2003-01-07T14:30:58Z")
The lower ray bends more than the upper ray so, in effect, you are seeing as an angle of (say) 14’ what is really an angle of 16’.