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  #561  
Old 19.02.2008, 09:54
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Re: Ask a Scientist

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Ummmm. . . . yes-ish. As per my understanding the medium through which the light travels has an effect on the actual speed so it's probably moving slightly slower than through space, a vacuum.
That's right. Because light travels a bit slower through air (or any other medium) than it does through a vacuum, it's actually possible to go faster than the local 'speed of light'. When you do that you get something rather analogous to a sonic boom. Of course, you can't do it in a vacuum.
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  #562  
Old 19.02.2008, 09:57
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The sun does rotate, about every 27 days, so does have an axis. And as just mentioned it moves back and forth in space due to the gravitational pull of the other planets. That's actually how astronomers are able to tell if stars have planets around them.
The sun also moves in an orbit around the centre of the galaxy. It takes about 200 million years to go round once.
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  #563  
Old 19.02.2008, 09:57
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Re: Ask a Scientist

Not wishing to be difficult but is space a vacuum given there are numerous gas nebulae etc ?

I thought the inside of a normal light bulb was a vacuum.
ash
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  #564  
Old 19.02.2008, 10:01
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Re: Ask a Scientist

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Not wishing to be difficult but is space a vacuum given there are numerous gas nebulae etc ?

I thought the inside of a normal light bulb was a vacuum.
ash
For the most part, space is a vacuum, hence the reason things explode in space. Inside the light bulb is a vacuum, outside the light bulb is not a vacuum. So the light ends up traveling at different speeds before it reaches your eye.

EDIT: dyslexia makes me get things backwards.
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  #565  
Old 19.02.2008, 10:06
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Re: Ask a Scientist

Good point. A true vacuum is more of a concept than a reality, as there are always bit of muck about. That said, most parts of space are pretty close to a vacuum, certainly better than anything we can make on earth.

I believe modern incadenscent light bulbs are filled with nitrogen or argon as a rule (albeit below standard pressure).
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  #566  
Old 19.02.2008, 10:07
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Re: Ask a Scientist

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For the most part, space is a vacuum, hence the reason things implode in space (boy do I love a good implosion). Inside the light bulb is a vacuum, outside the light bulb is not a vacuum. So the light ends up traveling at different speeds before it reaches your eye.
Now being deliberately difficult for the most part means that space is a partial vacuum Also things implode when subjected to external pressure i.e. where the pressure on the inside is less than the outside not vice versa.

A sudden reduction in pressure results in an explosion or embolism.

I like a good implosion too

ash
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  #567  
Old 19.02.2008, 10:08
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For the most part, space is a vacuum, hence the reason things implode in space (boy do I love a good implosion). Inside the light bulb is a vacuum, outside the light bulb is not a vacuum. So the light ends up traveling at different speeds before it reaches your eye.
How do you mean implode? If something is exposed to reduced pressure it would be more likely to explode, surely?
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  #568  
Old 19.02.2008, 10:10
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Re: Ask a Scientist

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Now being deliberately difficult for the most part means that space is a partial vacuum Also things implode when subjected to external pressure i.e. where the pressure on the inside is less than the outside not vice versa.

A sudden reduction in pressure results in an explosion or embolism.

I like a good implosion too

ash
Sorry, opposite day today. That's what I meant but sometimes I mix things up in my head.
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  #569  
Old 19.02.2008, 10:14
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but sometimes I mix things up in my head.
A pretty dangerous modus operandi given your profession

I always used a pestle and mortar

Sorry folks could not resist that one

Cheers
ash
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  #570  
Old 19.02.2008, 10:14
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Re: Ask a Scientist

Don't we all?

Don't go into bomb disposal though will you?
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  #571  
Old 19.02.2008, 10:48
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Re: Ask a Scientist

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Does the sun move? , sure we all know the planets orbit the sun , but does the sun just sit there, or does it rotate on its axis, or ...does it have an axis ?
A comment regarding popular knowledge and by which I don't mean to be disrespectful in any way: It's interesting and curious how, while it's nowadays common knowledge that the Earth is not the center of the universe, a lot of people have just shifted this center to the Sun, and are somewhat unsure about the Sun itself moves. This must be the result of the ominpresent pictures and models of the solar system (Sun in the center and planets orbiting around it), respectively the much fewer descriptions of the "bigger scale picture".

For the record, and to add an extra dimension (not in the mathematical sense): the Sun rotates around its own axis, wobbles a bit, revolves around the center of the galaxy, and the galaxy itself moves through space. We're just one of the little planets around a random star in the universe...
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  #572  
Old 19.02.2008, 10:53
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Re: Ask a Scientist

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The sun also moves in an orbit around the centre of the galaxy. It takes about 200 million years to go round once.

ok.. so where are we now in the orbit then.. I mean it's 10.52, make that 10.53 , and I have a date on Alpha Centauri
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  #573  
Old 19.02.2008, 10:56
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.
Hey, can someone here tell me how "exposure" works in a digital camera? I have a vague understanding of how traditional photography works, light exposing the silver halide, and fast vs. slow exposures, and "fast film" getting you grainier photos. But how does all this work with digital photography? And what the heck does image stabilization do anyway?
Just saw this one. I don't know about image stabilization, but I think I can answer the first bit. I think that cameras use CCD (Charge-Coupled Devices) just like telescopes do. Basically you have a semiconductor chip, and it's divided up into pixels, so ten million or whatever on a modern camera. Each pixel acts like a little capacitor, so it stores electric charge.

What happens when your photons, ie your light, comes in through the lens and hits the capacitors? Each time (well almost each time - it's not quite 100% reliable) a photon hits a pixel, that pixel gains some charge so you're literally counting photons!

Of course the photon isn't carrying any charge itself, so where does the charge come from? Well, the photon excites an electron (negative charge carrying particle) from one 'band' of the semiconductor to another, something which is possible because an electric field is applied to the capacitor. The real challenge comes in 'reading out' the CCD quickly into memory, especially in applications like video!

Hope that helps.
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  #574  
Old 19.02.2008, 10:58
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ok.. so where are we now in the orbit then.. I mean it's 10.52, make that 10.53 , and I have a date on Alpha Centauri
Unfortunately, Alpha Centauri is moving too....
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  #575  
Old 19.02.2008, 11:04
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Re: Ask a Scientist

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Just saw this one. I don't know about image stabilization, but I think I can answer the first bit. I think that cameras use CCD (Charge-Coupled Devices) just like telescopes do. Basically you have a semiconductor chip, and it's divided up into pixels, so ten million or whatever on a modern camera. Each pixel acts like a little capacitor, so it stores electric charge.

What happens when your photons, ie your light, comes in through the lens and hits the capacitors? Each time (well almost each time - it's not quite 100% reliable) a photon hits a pixel, that pixel gains some charge so you're literally counting photons!

Of course the photon isn't carrying any charge itself, so where does the charge come from? Well, the photon excites an electron (negative charge carrying particle) from one 'band' of the semiconductor to another, something which is possible because an electric field is applied to the capacitor. The real challenge comes in 'reading out' the CCD quickly into memory, especially in applications like video!

Hope that helps.
CCDs are used in Nikons for instance and consume a little more power and are also more prone to noise. Canon for example uses CMOS sensors which are much easier on your batteries. There are advantages to both.

IS- image stabilization - most commonly implemented on SLR lenses - stabilize your lens. If you know how a gyroscope works, it is pretty much the same effect (at least with the Canon IS system). Is counteracts any handshake you might have (or if you are shooting from a moving car or boat). Doing so you can get away with much slower shutter speeds and still have crisp results. Of course this only works if your subject is not moving. If the subject moves, the slow shutter speed will result in a blurred image either way...
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  #576  
Old 19.02.2008, 11:08
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Re: Ask a Scientist

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CCDs are used in Nikons for instance and consume a little more power and are also more prone to noise. Canon for example uses CMOS sensors which are much easier on your batteries. There are advantages to both.

IS- image stabilization - most commonly implemented on SLR lenses - stabilize your lens. If you know how a gyroscope works, it is pretty much the same effect (at least with the Canon IS system).
But CMOS works along broadly similar lines right?
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  #577  
Old 19.02.2008, 11:13
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Re: Ask a Scientist

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But CMOS works along broadly similar lines right?

Yes for the conversion part, no for the reading part..
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  #578  
Old 19.02.2008, 11:19
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Re: Ask a Scientist

I guess I was wrong about the noise statement:

Because of the manufacturing differences, there have been some noticeable differences between CCD and CMOS sensors.
  • CCD sensors, as mentioned above, create high-quality, low-noise images. CMOS sensors, traditionally, are more susceptible to noise.
  • Because each pixel on a CMOS sensor has several transistors located next to it, the light sensitivity of a CMOS chip tends to be lower. Many of the photons hitting the chip hit the transistors instead of the photodiode.
  • CMOS traditionally consumes little power. Implementing a sensor in CMOS yields a low-power sensor.
  • CCDs use a process that consumes lots of power. CCDs consume as much as 100 times more power than an equivalent CMOS sensor.
  • CMOS chips can be fabricated on just about any standard silicon production line, so they tend to be extremely inexpensive compared to CCD sensors.
  • CCD sensors have been mass produced for a longer period of time, so they are more mature. They tend to have higher quality and more pixels.
Based on these differences, you can see that CCDs tend to be used in cameras that focus on high-quality images with lots of pixels and excellent light sensitivity. CMOS sensors traditionally have lower quality, lower resolution and lower sensitivity. CMOS sensors are just now improving to the point where they reach near parity with CCD devices in some applications. CMOS cameras are usually less expensive and have great battery life.

Though in my experience, Canon SLRs which use CMOS have better IQ at hiher ISOs than Nikon that use CCDs, but maybe the sensor is not to blame, maybe something happens when the data is read/transported...?
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  #579  
Old 19.02.2008, 11:26
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Re: Ask a Scientist

Maybe, not quite sure what though. In astronomy we use CCDs because we don't want to miss a single photon. Sometimes an x-ray observation might be just a few tens of photons. Anyway, I think this might possibly be more detail than the original questioner wanted.

Last edited by ommthree; 19.02.2008 at 11:27. Reason: Adding content.
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  #580  
Old 19.02.2008, 12:44
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Re: Ask a Scientist

Here is a question only vaguely related to science itself--but nonetheless relevant:

I cannot communicate with my male bosses. I feel like they never value what I say, tell me to do one thing one week and act like I'm an idiot if I bring it up in the future, shoot down my ideas, and never give the input or guidance I ask for, aside from to say, "You should have done it like this" or "Why did you waste so much time on that?" I try very hard not to take it personally, because, intellectually, I know it's nothing personal, but as my PhD is my baby right now, this is easier said than done. I end up just avoiding them and going to other people for help....but sometimes it's the bosses' help that I really need.

I know why--it's because I am a woman and communication is fundamentally different for men and women, probably also I'm a young scientist and they are a lot more experienced.

My question is, what can I do about it? I'm interested if other Ladies of Science also find this a problem...maybe it's a major problem for me right now because I'm in the final stages of my Ph.D. I know I'd like a career in science if only I could handle dealing with other scientists :-P
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