It's a circumzenithal arc (google if you're curious, im on mobile). Someone else just posted a similar picture at /r/weather, I presume in the same place. They can be seen in certain circumstances where the sun is approximately 20 degrees above the horizon and there are thin cirrus clouds overhead.
Incidentally, since it is caused by sunlight traveling through ice clouds rather than raindrops, ...wazoheat 10/27/2012
It's not upside down, it's just that the sun is in front of you instead of behind you. The center of the circle is always on the line along the sun and your head.
Edit: Read wazoheat's comment, turns out I'm wrong. It's actually a circumzenithal arc. Because it forms via ice ...pyvlad 10/27/2012
97 people upvoted this ? What is wtf coming to? A god damn upside down rainbow?Luckystrike84 10/27/2012
The only thing WTF about this is that you thought this was interesting enough to post.jeblis 10/27/2012
Here, have an upvote for not putting "go home rainbow, you're drunk" in the title.SpecklePattern 10/28/2012
How do you know it's upside down. The tree could be upside sown in the sky. Checkmate atheists.asmo97 10/28/2012
I saw this one today too, there were actually three including one making a ring around the sun. It was pretty awesome.chunky47 10/27/2012
I saw the same thing while at work yesterday! There were three rainbows, actually. One upside-down, another sort of reflecting it, and a third was off to the side. Couldn't capture all three in the same shot though. Sorry it is hard to see, I only had my phone with me at the time.x13emma13x 10/28/2012
Dafuq i was at a farm in RI that had a corn maze yesterday and i saw the same thing...P0larized 10/28/2012
I think that it's now time for people to hate me because of Japanese culture...soundwafflez 10/28/2012
wow, not only is your post not the least bit wtf, it's kinda stupid, use google, its a new thing that helps you figure out things about the worldmalcolmxtacy 10/28/2012
I saw this poking through the clouds today...it was alarming - the weather's so funky there are bright sundogs shining through the clouds? Is this storm going to be nuts?Vileness_fats 10/27/2012
Saw this today also I was like stop it rainbow that's not how you're supposed to workspambot_3000 10/27/2012
saw that too..
I was in Yonkers.. there were 2 on either side of the sun.
as a kid I would always notice this phenom and tell my parents, they thought I was making it up.Tapeball45 10/27/2012
The leprechaun is in heaven now... oh crap here come all the atheists run! Its a stampede!!!!!Zshogan 10/28/2012
Don't worry. Just stand there, and eventually you will flip the right direction and it will all seem normal. :-0HermesTheMessenger 10/28/2012
I hope u know, its actually double upside down rainbows. Keep looking down and Ull see the second one just faintly.masahawk 10/28/2012
See that /r/WTF. Rainbows. Rainbows are now considered what the fuck material. Wow.Larry_The_Lobster 10/27/2012
>' The Almighty Lord proclaimith, "He who gazes uponith thy upside-down rainbow is aboutith to get fucked hardith." Amen.'StonedSoldier830 10/27/2012
its called a fuckin Chembow, it is reflecting due to Ice crystals with particulate matter...look the shit up, to nonbelievers...just readsattaman423 10/28/2012
Were there ponies? Pretty and sparkly ones? That would be a nice hurricane to have. ʕ•ᴥ•ʔ[deleted] 10/28/2012