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Sunlight absorbed in space?

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brianvds
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« on: January 30, 2013, 15:50:11 PM »

This quote is from a grade 8 science textbook*:

"Only 47% of the solar energy directed at the Earth reaches the surface of the Earth. The remaining 53% of the energy is absorbed in space."

---This doesn't sound right. Surely there isn't THAT much dust and gas between us and the sun? I couldn't find any information about this anywhere. Perhaps they meant to say 53% is absorbed by the Earth's atmosphere? Would that be true? Does anyone know anything about this issue? How much IS in fact absorbed in space?

*Oxford Successful Natural Sciences, Learner's book. Grade 8.
Authors: Fiona Clitheroe and Liz Dilley
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BoogieMonster
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« Reply #1 on: January 30, 2013, 16:02:27 PM »

I've read that a large amount of sunlight is reflected back out into space (barring the greenhouse effect). Such that having snow, which reflects the most wavelengths of light, helps cool the planet down (other than, of course, being cold) by making a good proportion of the rays head right back out.

I also very much doubt there's that much stuff between us and the sun. Moreover the statement seems misleading because the earth would only receive a very tiny fraction of "the solar energy". Most of the sun's energy goes in directions not intersecting with the earth.
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Rigil Kent
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« Reply #2 on: January 30, 2013, 16:18:47 PM »

Moreover the statement seems misleading because ... Most of the sun's energy goes in directions not intersecting with the earth.

"Only 47% of the solar energy directed at the Earth reaches the surface of the Earth. The remaining 53% of the energy is absorbed in space."
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BoogieMonster
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« Reply #3 on: January 30, 2013, 16:40:13 PM »

Eish, yeah, ok, obviously having a reading malfunction.
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Mefiante
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« Reply #4 on: January 30, 2013, 19:16:01 PM »

Quote from: Earth’s Climate System
On average, about 30% of the incoming shortwave radiation is reflected back to space, due to backscatter (reflection) from clouds (16%); air molecules, dust, and haze (6%); and Earth’s surface (7%; Fig. 2.3). Another 23% of the incoming shortwave radiation is absorbed by the atmosphere, especially by ozone in the upper atmosphere and by clouds and water vapor in the lower atmosphere. The remaining 47% reaches Earth’s surface as direct or diffuse radiation and is absorbed there (Trenberth et al. 2009).

Source., Section Earth’s Energy Budget (~5MB).
So yes, it’s predominantly the Earth’s atmosphere that reduces the amount of the sun’s incident radiation reaching the surface of our planet.

'Luthon64
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brianvds
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« Reply #5 on: January 31, 2013, 04:23:45 AM »

Mefiante: Thanks, that makes more sense. I have noted that the school textbooks often contain all manner of glaring errors of that sort, and I wonder how many teachers mindlessly teach that crap.

Yesterday the principal at the school where I work had all the assistant teachers write a grade 4 math exam. They all failed. They all have at least matric, and one actually has a B. Ed. degree.

Presumably, in another few years, a poll will find that 50% of South Africans believe that half of the sun's radiation is absorbed in space before it reaches Earth... Smiley
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