27 February 2007

How Loud is the Sun?

Unsurprisingly, being a closet geek, I love browsing through New Scientist magazine. Months and months ago now I submitted a question to a regular feature they run on the back page called “The Last Word” where readers can ask odd questions and other readers (usually scientists who are experts in the particular field to which the question relates) can answer them.
My question was along the lines of: “If the space between the Earth and the Sun was filled with air – but a hypothetical air whose only physical property was to transmit sound – then could we hear the sound of the Sun, and how loud would this be?” I had a wonderful vision in mind of the Sun peeking over the horizon every morning with a sound like some giant, yet distant, bowl of Rice Bubbles.
Well, for some months there I wasn’t keeping abreast of the latest issue of New Scientist. Then, about two months ago, I was wallowing in the air-conditioning at the Richmond Public Library, flicking through some of the issues I’d missed, when I discovered they’d published my question! Not only that, the issue I had in my hand wasn’t the one with the question, it was the later one where people have written in with answers! I was one excited little motherfucker.
But my glee was short-lived! Reading further, I discovered that to save space the editors had cut my question a little, knocking out the caveats about the hypothetical sound-carrying substance having no other physical properties. As a result a tidal wave of outraged geeks had written in attacking my question on its supposed inaccuracy, whining on and on about how the Earth couldn’t orbit the Sun with the drag created by so much air, and how that much air would collapse the solar system, and blah b’blah blah blah. One cunt had the gall to send in something saying, “The question seems to imply some sort of odd, pre-Copernican view of the solar system…” Piss off mate, I know the Sun’s at the centre. Christ.
Fine, I thought, I’ll figure it out myself then. So that’s what I spent a good deal of the weekend doing.
I started off with the idea of finding out how loud a 1-megaton nuclear bomb is, then how many megatons the energy produced by the Sun is equivalent to, then multiplying one by the other to get a decibel level for the Sun. Annoyingly though, I discovered our system for measuring sound is a bit of a bastard. The decibel scale is a logarithmic scale, which makes it very nasty to graph, so scaling the dBs from a 1-megaton nuke up to the dBs produced by the 91,467,495,219 megatons the Sun is equal to was a bit much for the addled remnants of my high school Advanced Vegie maths.
Besides that, explosions are apparently notoriously difficult to determine dBs for. The sound peaks very quickly, then trails off, and at higher dBs the sound becomes a shockwave, which behaves differently altogether.
Luckily, I found that dBs can be converted to watts and vice versa. The sun produces about 3.8e+26 watts every second, or 383 yottawatts (whatta lotta yotawatts… sorry), which, as you would expect, is an absolute pants-load of energy. This translates into 290dB, which is very loud indeed.
But, the Earth is 149,600,000 km away from the Sun. Applying the inverse square law, that tells us how sound intensity decreases with distance, I found the Sun would actually deliver about 125 dB here on the surface of the Earth – hardly a distant bowl of Rice Bubbles. 100dB is a jackhammer at 2 metres, 120 is your ear about a metre away from a train horn, and 130 is physical pain.
And what sound would you constantly hear at this excruciating level? Something like this, but immeasurably deeper: http://soi.stanford.edu/results/thr_modes_1_0_1_2_30s.au


Anonymous said...

Are you going to send this section of your blog into New Scientist to point out to them the error of their sloppy editing? Their presentation makes them look pre-Cornucopia, ahem, pre-Copernican in terms of their journalistic ability. Is this defamation? Oh well, it's an anonymous comment, or so I believe.

Alistair Spalding said...

Here's my question to the Last Word:

I see that conceptual artist Carsten Holler (the man who put slides in the Tate) has a new project on. 24 volunteers will be given goggles that invert their vision to wear for eight days. The idea is that they'll see the world upside down.
At the end of the time they will take their goggles off in front of an audience at the Manchester International Arts Festival in July. I got this from the London Metro, which says "Their sight is expected to return to normal shortly after."
I seem to remember from GSCE physics that if you hold prisms in front of your eyes (inverting your vision) that within a matter of hours the brain will compensate and flip your vision the right way up.
If that's true then within a few hours of putting the goggles on the volunteers will actually begin to experience normal vision again. Then on the eighth day, when they take them off they will see things upside down again for a few hours before, once again, the brain compensates and turns it back to normal.
Is this true? and if it is doesn't that kind of ruin his experiment? He should have the people at the show in Manchester put goggles on until their brain flips things the rightway up and then have them take them off again, putting things upside down (for a while).

Anonymous said...

answer the the above question:

That wouldn't be quite feasable, it takes quite a while for the brain to adjust to the new inverted vision. I think it was a few days for one lady who tried it. She got to where she could ride a bycycle and perform normally. Then they took them off of her and it took her a few hours to adjust back to normal.

My Year Without said...

I just asked my husband this question.

I found your blog and was very intrigued by the way YOU came to a consensus. Nice thinking.

It would be hilarious to ask 100 people this question and tape everyone's answers.....

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Oolong said...

I like it, only I think you might be confusing different usages of 'decibel' here - it would be very odd if wattage could be converted directly into a measure of sound, given a 100W bulb is so much quieter than a 100W speaker! It seems that decibels don't always refer to noise levels, surprisingly.

What a shame nobody came up with a good answer to your question for Last Word!

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