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Old 04-08-08, 06:23 PM   #1
East Hill
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Calculating the size of a rainbow

No, I haven't lost my mind (well, not today at least).

Mr. East Hill was musing today about how to calculate the apparent size of a rainbow. If this makes sense to anyone, could you please explain how to do this?

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Old 04-08-08, 06:25 PM   #2
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It is an algorithm based on the size of the pot of gold.
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Phobias are for irrational fears. Fear of junk ripping badgers is perfectly rational. Those things are nasty.
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Old 04-08-08, 06:28 PM   #3
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Using the widely accepted, industry standard stride length of a Leprechaun = 1.3 feet, count the number of steps he takes and multiply it by the stride length. This should give you the final distance. Note: if he's carrying his pot of gold make sure you reduce his stride length by a factor of 0.85.
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Old 04-08-08, 06:30 PM   #4
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Alfster, you are describing ground length of rainbow, but arch is dictated soley by pot of gold size. Once you know length and arch, then you are golden.
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Phobias are for irrational fears. Fear of junk ripping badgers is perfectly rational. Those things are nasty.
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Old 04-08-08, 06:37 PM   #5
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Alfster, you are describing ground length of rainbow, but arch is dictated soley by pot of gold size. Once you know length and arch, then you are golden.
Yes, but the likely hood of you catching a Leprechaun to determine his pot of gold is slim-to-none. Therefore standard stride measurements were implemented to determine length. This will give the chord length of the arc. I thought everyone knew that
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Old 04-09-08, 12:10 AM   #6
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The apparent size in terms of length and height in feet depends on how far away you decide to place it.

The size measured in radians/degrees is an absolute number and fairly easy to calculate.
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Old 04-09-08, 12:12 AM   #7
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Oh forget all of the above hooey. Just ask Jon. He would know.
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Old 04-09-08, 12:14 AM   #8
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For every gay person it grows in length G(3*1.4x)
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Old 04-09-08, 12:21 AM   #9
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For every gay person it grows in length G(3*1.4x)
Approximations are sloppy. More precisely it's G(3*sqrt(2)x).

Also, don't forget that the rainbow extends invisibly into the ultraviolet and infrared ranges. All you people are only considering the visible size of the rainbow.
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Old 04-09-08, 12:32 AM   #10
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Foooey on Jon! I have Ze Truth!!!

I've been taking my measured and calculated forefinger and thumb (my thumb btw is twice the size of Jsherr's - proven too) and have been seen around my area trying to measure using the "Crushy Your Head" theory.

So far... <squint> I'm thinking that rainbow is no more than 2" high and 5" long.

Does this help? If not, my Rainbow Crushy team is still on the road looking for new ones ...

Oh and if you see any of us on the road and being chased by people ... can you deter them so we can continue our quest?

Thank you.
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Old 04-09-08, 01:33 AM   #11
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Quote:
Originally Posted by East Hill View Post
No, I haven't lost my mind (well, not today at least).

Mr. East Hill was musing today about how to calculate the apparent size of a rainbow. If this makes sense to anyone, could you please explain how to do this?

East Hill
Google knows rainbows. Here's one place it found http://en.wikipedia.org/wiki/Rainbow
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Old 04-09-08, 01:50 AM   #12
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It is an algorithm based on the size of the pot of gold.
Pot of gold? Since when?

I always thought it was just pot.
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Old 04-09-08, 09:20 AM   #13
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This pot of gold?

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Old 04-09-08, 09:39 AM   #14
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Old 04-09-08, 09:47 AM   #15
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Assuming it's a semi-circular rainbow, find the length between each end and multiply by by pi*d/2

Else, find the distance and height and derive a quadratic equation.
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Old 04-09-08, 10:06 AM   #16
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A primary rainbow will always subtend a 42 degree radius from a line from the sun through your head. I suppose if you insist on an absolute size, you need a distance, so it's however far the rain line is from you.
I think the size is going to be 2 x distance x sin(42*) or about 1.3 x the distance from you to the rainbow (rain line)
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Old 04-09-08, 10:34 AM   #17
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Quote:
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Foooey on Jon! I have Ze Truth!!!

I've been taking my measured and calculated forefinger and thumb (my thumb btw is twice the size of Jsherr's - proven too) ...
Wait. That means your is twice the size of his too. I didn't think you had a Tude.
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Old 04-09-08, 10:48 AM   #18
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everbody's is twice the size of my

I make John Wayne Bobbit look like a draught horse

This based solely on the highly scientific, post your thumb thread, which clearly showed that I have freakishly short digits.
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Quote:
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Phobias are for irrational fears. Fear of junk ripping badgers is perfectly rational. Those things are nasty.
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