The Summer Moon Illusion

June 19, 2005 7:32 PM

For the sake of your sanity, for five minutes this week forget the memos, the autopsies, the celebrity verdicts, and the rest. Go outside and look at the full moon, which will hang in the sky at its lowest point in 18 years over the next three nights, says NASA, creating the "summer moon illusion." If you're a US resident, calculate your local moonrise time here.
posted by digaman (26 comments total)

This is awesome. Thanks!
posted by nyterrant at 7:41 PM on June 19, 2005

Thanks digaman,for such good advice.For those of you scientifically inclined use a large prism and make a spectrum of moon light,you will not belive the color density, really amazing.
posted by hortense at 7:44 PM on June 19, 2005

Driving home this evening I couldn't help but notice how big the moon looked. Thanks digaman and thanks ponzo's illusion!
posted by furtive at 7:47 PM on June 19, 2005

Thank you for the advice, which will be taken.
posted by juggernautco at 7:47 PM on June 19, 2005

While you're at it, check out an Iridium satellite flare - get the next time and coordinates from Heavens Above. These are amazing to try to hunt down and watch for.
posted by Fozzie at 7:50 PM on June 19, 2005

Thanks, Digaman. Just as I was reading your post, the Eagles started singing "Hole in the World" on Bravo. The two things reminded me of what is beautiful in this world: nature, music, love, and art.

I love it when things coincide this way.
posted by mmahaffie at 8:08 PM on June 19, 2005

I am nerdily excited! Now, just to wait until the moon comes up.
posted by Amanda B at 8:12 PM on June 19, 2005

This is very awesome. Thanks, dman. I'd never even thought twice about the moon looking bigger while lower in the sky. However, I do remember being very disappointed when my nine year-old self developed pictures I had taken of a fantastic moonrise and they turned up a teeny-tiny moon. I always thought it was my cheap little kid camera, but now I know there's an awesome optical illusion-type explanation!
posted by PhatLobley at 8:42 PM on June 19, 2005

I've only seen this once in my life, and it's definitely true. I'll be looking for it again this week.
posted by fungible at 9:23 PM on June 19, 2005

From the linked NASA article: What makes the moon so low? It's summer. Remember, the sun and the full Moon are on opposite sides of the sky. During summer the sun is high, which means the full moon must be low.

I don't get it. I mean, I'm fully aware of the illusion of the moon looking big when it's close to the horizon, but it's close to the horizon (or "low") EVERY DAY. It's called moonrise and moonset :)

Maybe they mean that at its highest point in the sky, it's still kind of low, and thos conditions happen in summer? I'm not convinced, and certainly not by their logic (the sun is high, therefore the moon is low? Wrong!)

Hopefully someone can explain it better than they did. They're NASA, so I do expect them to know what they're talking about, but I suspect that this article started out correct and then was run through the PR wringer and distorted. Like that "Mars will be as big as the moon" nonsense I keep having to correct.

Note: I built my own telescope, was looking at Jupiter's moons this evening, know my arc-secs from my parsecs, and have shown Iridium flares to plenty of people. So I'm not astronomically stupid ... so to speak ...
posted by intermod at 9:46 PM on June 19, 2005

Brilliant Digaman, I'll be passing along the info. :)
posted by dejah420 at 10:29 PM on June 19, 2005

Everybody sing!
posted by homunculus at 10:34 PM on June 19, 2005

TY Homunculus for going the extra mile.
posted by TangerineGurl at 11:00 PM on June 19, 2005

What I would like to know is a program or website to say exactly where on the horizon the moon will rise, at any given coordinate and date. I have a view to the southeast, and some nights, the moon is over the ocean, not others. Can anyone help?

This is good to know, thanks for the FPP!
posted by Goofyy at 11:45 PM on June 19, 2005

intermod, i imagine they mean at its lowest declination in the sky, which in turn means it is taking the lowest path across the sky, similar to the sun in winter vs. summer, with the summer solstice being the farthest point from the celestial equator that the reaches along its apparent path in the sky. at least that's what i think they mean.
posted by Igor XA at 12:03 AM on June 20, 2005

highest point is what i meant by "farthest point."
posted by Igor XA at 12:04 AM on June 20, 2005

intermod: what igorXA said.

The F'n Moon (mp3, NSFW)
inspired by:
This Brilliant Onion front page (NSFW)
posted by joeblough at 12:48 AM on June 20, 2005

can you export democracy to the moon?
posted by matteo at 4:47 AM on June 20, 2005

I'm with intermod. I get what they're talking about, but we can see this illusion all the time. (something nice about first year undergrad taking astronomy and psychology courses at the same time, finding things connect in ways you did not expect)
posted by dreamsign at 6:45 AM on June 20, 2005

I don't know if this is due to these current conditions, but last night when I was outside I was convinced it must be a full moon because there was so much light. I looked up and saw it wasn't full yet and kind of shrugged it off. I know, this is mostly about size, not brightness, but I'm gonna believe I was tricked by this cool atmospheric phenomenon.
posted by soyjoy at 7:51 AM on June 20, 2005

saw it last night--it looked noticably bigger and closer. : >
posted by amberglow at 8:43 AM on June 20, 2005

The article mentions you can make the illusion go away by looking through a "narrow opening of some kind". You can also make it disappear by turning your back to the moon, bending over, and looking at it upside down through your legs. It's fun, and leaves ample opportunity for "mooning" jokes.
posted by donnagirl at 9:33 AM on June 20, 2005

OK I just checked with the NASA site, and it turns out that just as the Sun's days are longer in the summer and shorter in the winter, the Moon's "days" are shorter in the summer and longer in the winter. This is not as I expected!! Pardon me if this is too much like an AskMe post, but can someone point me to some resources that explain why the Moon's "days" should lengthen and shorten at all? ( I know -- or think I know -- why the Sun's days do this, but I thought the Moon day was of more or less constant length)...
posted by bumpkin at 9:47 AM on June 20, 2005

bumpkin - it's the same reason as the sun's days get longer. The northern hemisphere is currently tilted as close to the sun as it gets over the course of a year. This causes any given point in the northern hemisphere to be able to see the sun for more hours out of the day. The full moon is always opposite the sun. Thus, the northern hemisphere is tilted *away* from the full moon (remember, the moon is pretty much in the same plane as the sun and earth, so it's roughly equator-level) in the same way as the southern hemisphere is currently tilted away from the sun. This causes the (full) moon to be lower on the horizon and be "up" for a shorter period of time.
posted by salad spork at 12:01 PM on June 20, 2005

Imagine my disappointment when I discovered that what I thought was a big moon was just a Ponzo scheme.
posted by Floydd at 12:52 PM on June 20, 2005

Solar sailing by moonlight
posted by hortense at 8:01 PM on June 20, 2005