# Why does the sun/moon look larger when near the horizon? **URL:** \ **Category:** Factual Questions\ **Created:** [April 17, 2002, 12:48pm UTC](https://boards.straightdope.com/t/why-does-the-sun-moon-look-larger-when-near-the-horizon/104119 "2002-04-17T12:48:24Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Nova1021](https://avatars.discourse-cdn.com/v4/letter/n/f05b48/32.png) [@Nova1021](https://boards.straightdope.com/u/Nova1021)\ **Post date:** [April 17, 2002, 12:48pm UTC](https://boards.straightdope.com/t/why-does-the-sun-moon-look-larger-when-near-the-horizon/104119/1 "2002-04-17T12:48:24Z")
Is it because of the atmosphere (which i’ve heard)? Or is it an illusion(which i’ve also heard)? ---
**Author:** ![UncleBill](https://avatars.discourse-cdn.com/v4/letter/u/d26b3c/32.png) [@UncleBill](https://boards.straightdope.com/u/UncleBill)\ **Post date:** [April 17, 2002, 12:56pm UTC](https://boards.straightdope.com/t/why-does-the-sun-moon-look-larger-when-near-the-horizon/104119/2 "2002-04-17T12:56:37Z")
The Master [speaks](http://www.straightdope.com/classics/a2_110.html). ---
**Author:** ![whitetho](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/whitetho/32/1059_2.png) [@whitetho](https://boards.straightdope.com/u/whitetho)\ **Post date:** [April 17, 2002, 12:57pm UTC](https://boards.straightdope.com/t/why-does-the-sun-moon-look-larger-when-near-the-horizon/104119/3 "2002-04-17T12:57:02Z")
Cecil addresses your question in [Why does the moon appear bigger near the horizon?](http://www.straightdope.com/classics/a2_110.html), which is also available in book form as part of _More of the Straight Dope_ (page 110). He discounts the atmosphere theory, and sides with the illusionists. ---
**Author:** ![sailor](https://avatars.discourse-cdn.com/v4/letter/s/a587f6/32.png) [@sailor](https://boards.straightdope.com/u/sailor)\ **Post date:** [April 17, 2002, 12:58pm UTC](https://boards.straightdope.com/t/why-does-the-sun-moon-look-larger-when-near-the-horizon/104119/4 "2002-04-17T12:58:33Z")
The short answer is that it is an optical illussion and the angular measurement is the same (in fact, a bit smaller) than when it overhead. ---
**Author:** ![UncleBill](https://avatars.discourse-cdn.com/v4/letter/u/d26b3c/32.png) [@UncleBill](https://boards.straightdope.com/u/UncleBill)\ **Post date:** [April 17, 2002, 1:04pm UTC](https://boards.straightdope.com/t/why-does-the-sun-moon-look-larger-when-near-the-horizon/104119/5 "2002-04-17T13:04:44Z")
And welcome to the Boards. The main Straight Dope page has a huge reservoir of information like this easily found with the Search function. By doing that before a General Question, and by doing a Message Board search before posting something that may have been done before, you will save a lot of people for rolling their eyes :rolleyes: and getting sarcastic. ---
**Author:** ![RM\_Mentock](https://avatars.discourse-cdn.com/v4/letter/r/e274bd/32.png) [@RM\_Mentock](https://boards.straightdope.com/u/RM_Mentock)\ **Post date:** [April 17, 2002, 1:17pm UTC](https://boards.straightdope.com/t/why-does-the-sun-moon-look-larger-when-near-the-horizon/104119/6 "2002-04-17T13:17:15Z")
The [Bad Astronomy](http://www.badastronomy.com/bad/misc/moonbig.html) take on it. ---
**Author:** ![Nova1021](https://avatars.discourse-cdn.com/v4/letter/n/f05b48/32.png) [@Nova1021](https://boards.straightdope.com/u/Nova1021)\ **Post date:** [April 17, 2002, 6:49pm UTC](https://boards.straightdope.com/t/why-does-the-sun-moon-look-larger-when-near-the-horizon/104119/7 "2002-04-17T18:49:24Z")
Ok, cool! I had heard it was an illusion, but it just seems so much bigger! Thanks guys! 🙂 ---
**Author:** ![DPWhite](https://avatars.discourse-cdn.com/v4/letter/d/d26b3c/32.png) [@DPWhite](https://boards.straightdope.com/u/DPWhite)\ **Post date:** [April 17, 2002, 6:56pm UTC](https://boards.straightdope.com/t/why-does-the-sun-moon-look-larger-when-near-the-horizon/104119/8 "2002-04-17T18:56:28Z")
Cecil’s paperclip response has always been less than rigorous in my mind. You can move your shoulder, head or elbow a little and are measuring something different. [http://www.lhup.edu/~dsimanek/3d/moonillu.htm](http://www.lhup.edu/~dsimanek/3d/moonillu.htm) by Donald E. Simanek has the best explanation and says that photographic negatives show that there is very little difference in the size (which assumes he did just that with a fixed focal length lens) and then explains the optical illusion. ---
**Author:** ![Podkayne](https://avatars.discourse-cdn.com/v4/letter/p/edb3f5/32.png) [@Podkayne](https://boards.straightdope.com/u/Podkayne)\ **Post date:** [April 17, 2002, 6:58pm UTC](https://boards.straightdope.com/t/why-does-the-sun-moon-look-larger-when-near-the-horizon/104119/9 "2002-04-17T18:58:32Z")
A beautiful illustration that the Moon Illusion is indeed just that: [http://antwrp.gsfc.nasa.gov/apod/ap020130.html](http://antwrp.gsfc.nasa.gov/apod/ap020130.html) This page also has some links to some exhaustive webpages with various hypoetheses to explain the phenomenon. Next time you see a huge-looking moon on the horizon, look at it up-side down. Stand on your head, or bend over and look at it from between your knees, or whatever your acrobatic ability and/or dignity will permit. The moon will be magically reduced to its normal size! Crazy! ---
**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:** [April 17, 2002, 7:39pm UTC](https://boards.straightdope.com/t/why-does-the-sun-moon-look-larger-when-near-the-horizon/104119/10 "2002-04-17T19:39:38Z")
I will second Simanek’s page, and note that I relied on it fairly heavily for the chapter in my book about the Moon Illusion. Tersely, it’s a combination of the [Ponzo Illusion](http://www.unmuseum.org/exmoon.htm) and the fact that we perceive that the sky is bowl-shaped (flattened near the zenith), making the horizon look farther away than the zenith. It _is_ an illusion, and not real. It’s the most convincing illusion I have ever seen, but nonetheless, it ain’t real. ---
**Author:** ![Terminus\_Est](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/terminus_est/32/3087_2.png) [@Terminus\_Est](https://boards.straightdope.com/u/Terminus_Est)\ **Post date:** [April 17, 2002, 11:45pm UTC](https://boards.straightdope.com/t/why-does-the-sun-moon-look-larger-when-near-the-horizon/104119/11 "2002-04-17T23:45:52Z")
Everyone is talking about the moon illusion, which has been adequately explained. But what about the Sun? I’ll argue that it looks bigger near the horizon due to atmospheric refraction, which also causes the orange color and the apparent change in shape to oval. ---
**Author:** ![rowrrbazzle](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rowrrbazzle/32/414_2.png) [@rowrrbazzle](https://boards.straightdope.com/u/rowrrbazzle)\ **Post date:** [April 18, 2002, 2:30am UTC](https://boards.straightdope.com/t/why-does-the-sun-moon-look-larger-when-near-the-horizon/104119/12 "2002-04-18T02:30:38Z")
Here’s an article about this from January 2000 with animated demonstrations: [http://www.research.ibm.com/resources/news/20000103\_moon\_illusion.shtml](http://www.research.ibm.com/resources/news/20000103_moon_illusion.shtml) > [@](#): > > In most cases, the terrain provides a rich set of cues that enable us to accurately perceive the sizes of objects at different distances, Professor Kaufman added. But apparently such large distances as those to the moon are beyond our brain’s capability. As an example, Professor Kaufman recommends viewing the moon through an aperture, such as pinching it between your thumb and forefinger or viewing it through a tube, which hides the the terrain leading up to the moon. The moon suddenly appears to be small because our brain locates it at the nearby distance of the edges of the aperture. Removing the aperture restores the terrain’s distance cues and the moon springs back to its large, illusory size. ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [April 18, 2002, 3:03am UTC](https://boards.straightdope.com/t/why-does-the-sun-moon-look-larger-when-near-the-horizon/104119/13 "2002-04-18T03:03:11Z")
Atmospheric refraction makes the sun smaller in the vertical direction, and no change in the horizontal direction. If something appeard wider because of atmospheric refraction, do all constellations appear wider near the horizon? How can everything along the horizon get wider and still fit in 360 degrees? ---
**Author:** ![Algernon](https://avatars.discourse-cdn.com/v4/letter/a/a183cd/32.png) [@Algernon](https://boards.straightdope.com/u/Algernon)\ **Post date:** [April 18, 2002, 3:09am UTC](https://boards.straightdope.com/t/why-does-the-sun-moon-look-larger-when-near-the-horizon/104119/14 "2002-04-18T03:09:21Z")
> [@](#): > > \*Originally posted by Terminus Est \* > Everyone is talking about the moon illusion, which has been adequately explained. But what about the Sun? It is exactly the same phenomenon as with the moon. Here is how I learned it in my Psychology of Perception course many years ago, which explains the Ponzo Illusion too. Mathematically… Perceived size = retinal image size \* perceived distance. In normal circumstances, when the cowboy rides off into the sunset for example, the retinal image size decreases as the perceived distance increases, so the perceived size stays the same. This is how our brain understands that everything is not actually changing size when the retinal image size changes. With the moon (or sun) setting, as others have indicated, the perceived distance increases due to the fact that people perceive the sky as a flattened bowl, _but the retinal image size stays the same,_ therefore the perceived size of the moon (or sun) when it is at the horizon is larger than when it is overhead. This effect is apparently magnified slightly by the trees and houses on the horizon, but this is not necessary for the effect to occur, as anyone who has seen the sun set on the ocean horizan can attest. ---
**Author:** ![Terminus\_Est](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/terminus_est/32/3087_2.png) [@Terminus\_Est](https://boards.straightdope.com/u/Terminus_Est)\ **Post date:** [April 18, 2002, 4:54am UTC](https://boards.straightdope.com/t/why-does-the-sun-moon-look-larger-when-near-the-horizon/104119/15 "2002-04-18T04:54:09Z")
So why is it that the sunset looks decidedly non-circular? **scr4** ’s explanation about refraction in the horizontal direction makes sense, but I’ve never seen the moon look that way. Why the difference? ---
**Author:** ![Terminus\_Est](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/terminus_est/32/3087_2.png) [@Terminus\_Est](https://boards.straightdope.com/u/Terminus_Est)\ **Post date:** [April 18, 2002, 4:59am UTC](https://boards.straightdope.com/t/why-does-the-sun-moon-look-larger-when-near-the-horizon/104119/16 "2002-04-18T04:59:42Z")
So why is it that the sunset looks decidedly non-circular? **scr4** ’s explanation about refraction in the horizontal direction makes sense, but I’ve never seen the moon look that way. Why the difference? ---
**Author:** ![Joe\_Cool](https://avatars.discourse-cdn.com/v4/letter/j/ecb155/32.png) [@Joe\_Cool](https://boards.straightdope.com/u/Joe_Cool)\ **Post date:** [April 18, 2002, 5:47am UTC](https://boards.straightdope.com/t/why-does-the-sun-moon-look-larger-when-near-the-horizon/104119/17 "2002-04-18T05:47:42Z")
I used to think (adamently) that it was a refraction effect, until one day I actually measured the ‘giant’ moon by holding up a pencil. It is amazing how much smaller it looks when you’re measuring it objectively. It is, in fact, the same size as when it’s directly overhead, much to my disappointment. ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [April 18, 2002, 6:19am UTC](https://boards.straightdope.com/t/why-does-the-sun-moon-look-larger-when-near-the-horizon/104119/18 "2002-04-18T06:19:41Z")
The sunset looks non-circular because of refraction. It’s hard to describe without diagrams, but basically you are looking through a thick, curved layer of air. That distorts the image. The moon should look exactly the same at the same position. I’m not sure why you haven’t seen it. Maybe because the moon isn’t very bright when it’s so low in the sky and you haven’t noticed it? ---
**Author:** ![ubergoober](https://avatars.discourse-cdn.com/v4/letter/u/ee7513/32.png) [@ubergoober](https://boards.straightdope.com/u/ubergoober)\ **Post date:** [April 18, 2002, 2:20pm UTC](https://boards.straightdope.com/t/why-does-the-sun-moon-look-larger-when-near-the-horizon/104119/19 "2002-04-18T14:20:20Z")
I was another one who was never sure it was an illusion. Looking at constellations convinced me. Currently Orion looks _hyooge_ compared to a few months ago, and Leo looks like it’s getting bigger as it moves from the zenith to the horizon. ---
**Author:** ![Terminus\_Est](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/terminus_est/32/3087_2.png) [@Terminus\_Est](https://boards.straightdope.com/u/Terminus_Est)\ **Post date:** [April 18, 2002, 3:17pm UTC](https://boards.straightdope.com/t/why-does-the-sun-moon-look-larger-when-near-the-horizon/104119/20 "2002-04-18T15:17:37Z")
Crap. Sorry for the double post. I believe I’ve seen my fair share of moonrises and moonsets; granted not as many as sunsets. (Sunrise? What’s that?) But I’ve never noticed the distortion effect. One factor could be moon phases - we’ve all seen the moon in different shapes, so a misshapen full moon on the horizon is not particularly remarkable. [Next page](https://boards.straightdope.com/t/why-does-the-sun-moon-look-larger-when-near-the-horizon/104119.md?page=2)