General Questions

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They can do spectrum analysis on the light the star produces. Each element has a very specific light-frequency signature produced as it burns, which can be used rather like DNA mapping to identify the specific elements in a given compound.
 
Because they put stars in to different classes depending on what they do, don't they?
 
Stars are mostly classed by size and light output. There are 7 classes (alpahbetic) and each class has 10 sizes. However, not all letter classes contain all number sizes, just because of stellar physics - certain types of stars are always certain sizes.

I just googled and came up with this:

http://www.astrophysical.org/starclassification.php
 
Sureshot
How do we know what stars contain/produce what metals?
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In addition to Duke's answer about directly looking at the spectrum of a star to see what elements are present, there is also the study of the processes involved in creating elements... although the absolute origin of matter is a matter of great mystery/debate, the origin of heavy elements is not: they come about through various types of nuclear reactions in the dense, hot cores of massive stars.. (see the wiki article on stellar nucleosynthesis for more details). Also, check out this classic paper by Arno Penzias on the origin of the elements... Penzias also won the Nobel Prize in Physics for co-discovering the cosmic microwave background, which is now the cornerstone of Big Bang theory...
 
Why is glass clear? What allows glass to allow light to pass through it, a solid object, yet paper can't pass through a sheet of paper?
 
Short answer: Because glass doesn't absorb light, and doesn't reflect all of it.
 
First of all, glass is technically a liquid, and second of all, I think you'd better check the wording of that post. I don't have a full answer but I do know that one little fact.
 
Everything absorbs electromagnetic waves. Glass happens to absorb very few electromagnetic waves from the spectrum visible to humans, while paper absorbs more.

Think about this: X-rays are also part of the electromagnetic spectrum. When you take an x-ray, the waves mostly pass right through your body, except for the bones – in other words, from the point of view of the x-ray spectrum, flesh is transparent, and bones are mostly opaque. So if you had eyes that could see in the x-ray spectrum but not in the visible light spectrum, people would look like walking bones.

We happen to be able to see a very very very narrow part of the electromagnetic spectrum (I’m not sure why we evolved to see the particular part that we do). BTW, you might want to watch this video by the inimitable Richard Feynman:

 
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Casio
yet paper can't pass through a sheet of paper?
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Well it could if you tried hard enough. :sly:

I'm assuming you meant "yet light can't pass through a sheet of paper". Well if you rub greasy food on it, it turns opaque, and if it does, it's your window to weight gain! :lol:
 
Sage
Everything absorbs electromagnetic waves. Glass happens to absorb very few electromagnetic waves from the spectrum visible to humans, while paper absorbs more.
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Why does it absorb fewer electromagnetic waves?
 
Well, that requires an in-depth conversation about several chemistry and physics topics, but suffice to say it’s a combination of subatomic, atomic, and molecular properties. Here’s a way over-simplified analogy: If you send an earthquake (which is a kind of wave energy) through water, it takes many miles for the wave energy to dissipate – for our purposes, you can basically say that the earthquake waves pass through unperturbed. Now stick a huge block of iron in that water. The waves that hit that block of iron will practically stop. So in this analogy, the water is “transparent” to the earthquake waves, while the iron block is “opaque”.
 
Casio
Why does it absorb fewer electromagnetic waves?
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Subtle but important point...

Sage
Glass happens to absorb very few electromagnetic waves from the spectrum visible to humans
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...in other words, glass still absorbs plenty electromagnetic radiation, just not at wavelengths that we can see - normal glass is not transparent to UV light, for example. The transparency of glass depends entirely on the eyes that are looking at it... clearly, glass is transparent to my sister's Greyhound too, judging by the number of times she has careered straight into the patio doors :ouch:

Sage
I’m not sure why we evolved to see the particular part that we do
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That's a good point/question... I found this, which goes some way to addressing that issue...

http://www.iop.org/EJ/article/0031-...quest-id=027b2828-d155-4848-a69b-6f2d21e0dcde
 
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Ok, last summer on my flight back from California, I was on a boeing 777. The speedo read out that the plane was travelling at over 700 MPH (No, not KPH that read out even higher), However I thought that a 777 had a cruise speed of only about 565MPH?
 
Well according to some googling maximum cruise speed is 567mph but that is at a cruise height of 35,000 ft. Maybe you were higher than that...
 
The speed being displayed was probably the ground speed, which depending on the tailwind, can be alot higher than the air speed of the plane...
 
Probably because it is a more useful thing to show people than the air speed of the plane... the "ground" speed is the speed of the plane plus the speed of the air, so it is a better reflection of the speed of the plane relative to the distance on the ground you are covering.... and besides, showing people that you can go 700 mph is much cooler than 565 mph :p

daan
Nice one. 👍

You just can't resist, can you?
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:lol: I didn't see that one...
 
Sage
I’m not sure why we evolved to see the particular part that we do
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Because it is the visible spectrum. DUH!

You guys make this more complex than it is when it is right there in the name.





Lord, help my kids when they start asking me serious complex questions. :sly:
 
What would happen to you if you ate that wee packet of silica gel?

I know it says "do not eat" on it, but I want to...
 
daan
What would happen to you if you ate that wee packet of silica gel?

I know it says "do not eat" on it, but I want to...
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From chow.com:
We’re not sure why you would, but if you’ve eaten one by mistake, you’ll likely be fine. According to Mike Yudizky, a recently retired paramedic and the public health educator at the North Texas Poison Control Center, “It’s nothing more than a type of sand. Despite the big-time warnings, it’s completely nontoxic.” Even if you were to eat a shoebox full of packets, the only result would be “an upset tummy. But the same would happen if you drank too much water.” The grains of what looks like clear caviar in the tiny packets are a desiccant. That is, they absorb moisture. You find them in food products that will have a longer shelf life if they stay dry. That could include pepperoni, dried nuts and fruits, or vitamins.
So why do the packets include warnings, occasionally including a skull and crossbones? To avoid product liability cases, says Yudizky. The packets are “harmful if swallowed by an infant or pet, as they could choke or aspirate on the silicon gel packet,” explains Michelle Musallam, a certified physician’s assistant in Dallas, Texas.
In some cases, the stuff is coated with a moisture indicator such as cobalt (II) chloride, a toxic substance that may be carcinogenic. But Yudizky says even that wouldn’t be a problem because of the incredibly small amount involved.
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That's quite disappointing. Going by the warning, it should suck all your water out and you'd die, and all that would be left of you is a pile of sand.
 
Buuuut... if you ate some in a Chevrolet, you could be in a Cobalt with cobalt in you!
 
daan
That's quite disappointing. Going by the warning, it should suck all your water out and you'd die, and all that would be left of you is a pile of sand.
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Actually, that is what happens. The site quoted was lying, just in case someone thought it'd be a good method of killing themselves. If you eat a pack of silica gel, which specifically says "Do not eat" on the packet, then all of the water in your body will be sucked out and you will DIE!!!!!!!!!

;)
 
Milford Cubicle
Actually, that is what happens. The site quoted was lying, just in case someone thought it'd be a good method of killing themselves. If you eat a pack of silica gel, which specifically says "Do not eat" on the packet, then all of the water in your body will be sucked out and you will DIE!!!!!!!!!

;)
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But then, if someone poured some water over that pile of sand, would you come back to life?
 
daan
But then, if someone poured some water over that pile of sand, would you come back to life?
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Wait didn't they do this in the old 1960's Batman movie?
 
And an episode of Star Trek (the original series).
 
Cheers guys, It may have actually been ground speed, and we were flying at higher than 35k feet aswell:tup:
 
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