[tweener]

quote:Originally posted by cuso4

Is this called the BLACK BODY RADIATION? Never mind me if I'm talking rubbish.

Angel

Black Body Radiation is correct.  The spectrum of the radiation given by any body that has a temperature above absolute zero has a certain shape and the location of the peak and the distribution change with temperature.  So, it doesn't matter what the body is made of, you can measure its temperature by measuring the radiation it emits.

The universe is emitting radiation in the microwave range (wavelength of several cm) which gives it a temp of about 3 degrees Kelvin.  Red hot steel is emitting in the red end of visible light (wavelength about 700 nm), and the Sun emits in the visible and higher (wavelength around 500 nm) with a surface temperature of 5800 K.  The core is about 15 million degrees K.

To find out what it is made of, again measure the radition, but look for other things.  Each element and molecule will emit or absorb radiation strongly at certain wavelengths.  Looking at the spectrum, these appear as bright or dark lines.  The selectivity is caused by the quantum nature of the electrons in the outer part of the atom or molecule and how the electrons can behave in their orbits. Each element and molecule is very distinct.  Because they are all bunched together, the lines are spread out because of all the collsions the particles are undergoing.

Another book, but this is fun!

John

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No words of wisdom here.

[NakedScientist (OP)]

Since John explained it so beautifully, there is virtually nothing I can add to the answer to last week's question "How do we know how hot the sun is?". The answer is indeed by spectroscopy - the colour of the sun indicates its surface temperature. Some experienced steel workers can predict, to within 1 degree accuracy, the temperature of their steel, just by looking at its colour.

Well done everyone.

TNS

[NakedScientist (OP)]

Here is this week's Question of the Week :

"HOW DO BACTERIA BECOME RESISTANT TO THE EFFECTS OF ANTIBIOTICS?"

Have a stab below...

TNS

[Ians Daddy]

I know it's layman and probably sounds silly, but my guess is like a military strategy. Like keeping your friends close and your enemies closer. They bond to the antibiotic and learn all they can of it's make up. They record a memory of it and restructure to accomidate it. At that point, they are immune because they are somewhat related. Just like snake venom used as the anti-venom. I really don't know, I just thought I'd take a guess. I figure I've got 50/50 odds of being right or wrong.

Just a thought.

[bezoar]

Sounds like a layman's description of mutation to me.  Pretty astute. Then too, bacteria like to exchange DNA when they sit together side by side.  I hear it's only a matter of time before we get a Vancomycin resistance staph strain, from exchanging DNA with the Vancomycin resistant enterococcus.  Heard of a couple of scares recently, but no confirmations.  What was thought to be Vancomycin resistant did respond, but only after lengthy treatment.  If anyone has ever read the book The Coming Plague, it'll give you a good scare, but a fascinating book.

[nilmot]

Change their antigens?

Have caspules so they're hard to engulf?

Just some guesses....

Tom

[Donnah]

I'm guessing that if we don't finish the course of any antibiotics we take, or if the course is not effective in killing the bacteria then the bacteria learn to recognize the antibiotics (as Ron said) and it's like the bacteria have been vaccinated against the antibiotics.

[cuso4]

Each generation of bacteria produces quite fast, so there are always some bacteria survive under the presence of antibiotic. These bacteria then reproduce and create the next generation. This will eventually lead to a mutation in the genes of bateria.

Angel

[MarkH10178]

I was just looking into this one. Those little bacteria are so damn smart - but I forget exactly how they do it. Transposons, something like that. They actually develop the ability to degrade the antibiotic that was meant to knock them off, by producing an enzyme that breaks it up. "Penicillinases" - something like that.

May I suggest a famous question? A while back somebody ran around the Harvard graduation ceremony with a videocam asking these supposedly smartest of all smart kids the question: "Why are there seasons?" - they had the worst time trying to get it right!

[Qing]

Is the resistance temporary or permanent?Would you feel that if you start using the same antibiotics after quiting for a long time,it becomes effective again? Does that mean the bacteria are not resistant to the antibiotics any more?

Qing

[NakedScientist (OP)]

ANSWER TO THIS WEEK'S "QUESTION OF THE WEEK"

HOW DO BACTERIA BECOME RESISTANT TO ANTIBIOTICS ?

You've all pretty much got the answer right. The mechanism of bacterial anti-microbial resistance comes down to them making a fortuitous mistake when they are copying their DNA.

Because bacteria grow so rapidly they need to copy their DNA rapidly. Occasionally this leads to an error creeping into the genetic code. Most of the time bugs which inherit these errors are at a growth disadvantage because all of the other bugs grow much better than them and hence they are out-competed and disappear.

But if the genetic mistake changes a bacterial protein so that an antibiotic can no long bind on to it, or another enzyme made by the bacterium gains the ability to chew up antibiotics molecules (as well as doing what it did before), now the mutant bacterium has a significant growth advantage whenever that antibiotic is around. All the non-resistant bugs are killed, leaving the resistant bacterium to father a new population of resistant mutants. With all of the competing bugs gone the new mutants enjoy life without any competition - rather like the shrimp fishing in forrest gump !

So the long and the short of it is, the more antibiotics you use, the more resistance you will see. It is a fortuituous mistake on the part of the bacteria. It comes down to the principles of Darwinian natural selection.

TNS

[NakedScientist (OP)]

We liked MarkH's suggestion, so this week's question is :

WHY ARE THERE SEASONS ?

Happy debating,

TNS

[cuso4]

The Earth spins on its vertical axis at an angle (I forgot the exact value). As a result, different part of the planet receive different amount(strength) of sunlight creating seasons. This really needs a good diagram to explain properly.

In the summer of a location, the place is slightly closer to the sun and so receive slightly stronger sunlight. In the winter, the place is slightly away from the sunlight so receive slightly weaker sunlight. This also explains why places near the poles have longer daylight in the summer than those near the equator.

As to the changes in the way plants and animals behave also depend on seasons . For example, the hibernation in bears (don't know whether this apply to other hibernating animals or not) is triggered by the change in length of daylight. And people seem to be happier in summer is because seratonine is only produce in sunlight (providing you're not taking anything). This is the substance that stimulates the productiion of noradrenaline.

Angel

"Anyone who has never made a mistake has never tried anything new." -Albert Einstein

[george]

I take on board what you've said Angel, about the planet being at an angle as it spins, but what makes the seasons change then ? How does the earth alter its degree of tilt; first it tilts one way, closer to the sun for one hemisphere, then the other. How does that happen ?

[UScaV]

The earth is always tilted at the same angle, which is 23.5 degrees.  The tilt of the earth is always the same and doesn't change.  So as the earth rotates around the sun, the angle changes depending on where the earth is.  That's why it happens at the same time of year each year.  There are 2 equinoxs and 2 solstices a year, and on the winter solstice, the Northern hemisphere is tilted as far away as it possibly can be, and during the summer as close as it possible can be.  Also, twice a year, the the angle to the sun of both hemispheres is the same, and the amount of light and length of day are pretty much equal all over the earth(equinox).

And I don't think winter and summer have to do with the amount of time light is hitting the earth, but rather the distance is has to travel, either fighting it's way through a longer distance and more atmosphere, or a shorter distance and a smaller amount of atmosphere.

[cuso4]

George, I think UScaV answered your question. Well explained UScaV.

"Anyone who has never made a mistake has never tried anything new." -Albert Einstein

[george]

Oh right. I think I've got it now. Thanks for explaining that so clearly !

George

[UScaV]

I wasn't sure about that last little bit.  Is that one right, where it just has to go through more atmosphere and space?

[tweener]

Actually, the distance from the earth to Sun is so close to constant year round, that it has nothing to do with temperature.  The difference in seasons is because of the tilt making the light strike at a greater angle (during winter).  This means that for a sunbeam of a given area, there is more surface area for it to cover (and thus less light energy per unit area). The atmosphere is so thin as to make little difference in terms of distance traveled.  

As an example of this, get a flashlight with a narrow beam, shine it straight down.  Then from the same height shine it at an angle (the greater the angle the more pronounced the effect).  You can see that it appears brighter in the straight down configuration and that the beam is covering a smaller area.


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John

[Quantumcat]

Also, the part of the earth tilted toward the sun is closer, so the heat has dissapitated less by the time it gets there and it's warmer. There's longer days in summer because the part of the earth you're on gets a wider light spread (if you've ever seen a Geochrome [is that what they're called? I can't remember] then you'll know what I mean.)

Am I dead? Am I alive? I'm both!