Science questions not worth a thread I: I'm a moron!

[Cheezy the Wiz]

Originally Posted by kristopherb

EMP, I know they are real, but how do you make one happen outside of nuclear weapons?

Apart from the methods GoodGame described, I believe solar wind and other solar phenomena produce what can be described as an EMP. A solar flare in the 19th century famously allowed telegraphs to be operated even though their power source had been shut down by that same flare.

[PlutonianEmpire]

How do I observe the Venus transit with my small refracting telescope? It's small, but the lid for the aperture has a smaller lid at the center that can be taken off. I don't have any filters, so the only thing I can do is use it to project the sunlight on a flat surface. Really, my concern is, will the sunlight damage the eyepiece? Or would it be better to remove the eyepiece for the projection method?

[uppi]

Sunlight has an intensity of about 0.1 W/cm^2, which is almost nothing in optics. Even at 100x magnification, this is not that much. So I wouldn't worry about damaging the eyepiece. But the magnification might be too large for a good projection, so it might work better without it.

[Saxony]

If nothing is faster than light how managed the Universe expand to 1 light year after just 1 second?

[Michkov]

Originally Posted by Saxony

If nothing is faster than light how managed the Universe expand to 1 light year after just 1 second?

Object cant move faster than light, space can. Just like far away parts of the universe are receding at speeds faster than light.

[Cutlass]

On any given day, what percentage of Earth's surface is obscured by cloud cover as seen from space?

[Michkov]

Originally Posted by Cutlass

On any given day, what percentage of Earth's surface is obscured by cloud cover as seen from space?

~70%

[tokala]

Originally Posted by uppi

Sunlight has an intensity of about 0.1 W/cm^2, which is almost nothing in optics. Even at 100x magnification, this is not that much. So I wouldn't worry about damaging the eyepiece. But the magnification might be too large for a good projection, so it might work better without it.

Hopefully not to late, but that's a dangerous assumption. Obviously the glass itself won't absorb enough energy to get damaged, but the area surrounding the eyepiece lens elements (or secondary mirror of a reflector) tend to be good absorbers. You get distracted for a moment, the sun moves out of the FOV, and very bad things can happen.

[peter grimes]

Originally Posted by tokala

Hopefully not to late, but that's a dangerous assumption. Obviously the glass itself won't absorb enough energy to get damaged, but the area surrounding the eyepiece lens elements (or secondary mirror of a reflector) tend to be good absorbers. You get distracted for a moment, the sun moves out of the FOV, and very bad things can happen.

Uh-oh... I wonder if I damaged my binocs then.

Wait - probably not, now that i think about it. There's a mirror in inside which keeps the light moving along the center of the tubes, right? So unless things become mis-aligned inside the case, the light should pass harmlessly through.

I think....

[tokala]

If you notice nothing out of the ordinary while looking through it, it should be fine.

It shouldn't be problematic, as long as you don't keep them pointed almost exactly at the sun. In that case the energy will end up highly concentrated inside the tubes.

Energy density near the focus will scale with the square of the objective diameter. That burned out Dobson looks like 16" or thereabouts, for the singed eyepiece a few seconds through a 3" scope were sufficient.

Next time I would suggest to use a proper filter though (proper as in front of the objective, NOT in front of the eyepiece)

[peter grimes]

If you notice nothing out of the ordinary while looking through it, it should be fine.<br />
<br />
It shouldn't be problematic, as long as you don't keep them pointed <i>almost</i> exactly at the sun. In that case the energy <i>will</i> end up highly concentrated inside the tubes.<br />
<br />
Energy density near the focus will scale with the square of the objective diameter. That burned out Dobson looks like 16" or thereabouts, for the singed eyepiece a few seconds through a 3" scope were sufficient. <br />
<br />
Next time I would suggest to use a proper filter though (proper as in front of the objective, NOT in front of the eyepiece)

There were times the light wasn't perfectly centered at the exit of the eyepiece. I took some guesswork to get it lined up. But even so, there were only intermittent full-sun conditions.... I'm probably ok.

But I want to project the sun the summer with my little cousins. I'll be more careful then.

When you say to use a filter, what sort do you mean? Neutral density? Polarizing?.. specific wavelengths?

[tokala]

With a normal filter, the brightness of the sun would have been reduced approximately to that of the full moon, suitable for direct viewing, but not for projection anymore.
Back in the day I used that stuff:
http://www.baader-planetarium.com/so...fi_start_e.htm

and mounted it in a cardbord frame like that:

Make sure to secure the frame with stickytape or somethink like that if you use such a contraption.

If you have some kids around, it's probably safer to use the projection method, though.
Better a damaged instrument than a destroyed eye!

And a low-powered binocular should be about the most robust instrument for solar projection, with a large FOV and relatively big eyepiece lenses.


Edit: It cannot emphazised enough that an unprotected view at the sun through even the smallest optical instrument will almost guarantee instant and permanent eye damage up to and including complete blindness!

[peter grimes]

Thanks, tokala. That's what I know as neutral density filter. It doesn't prefer any specific wavelength, it's not discriminatory.

If I were going to be really ambitious I'd try to set up a poor-man's tracking platform using an arduino and some photocells. But I only have a week at the lake, and I doubt my wife will be very happy if I spend the whole time ignoring her

The thing I like about the projection method is that everyone can see it, you can easily do some sketches over a couple of days to see how the sun changes, and it's pretty quick to set up. I just hope the kids are as excited about it as I am

[contre]

One way of thinking of a multiverse is an eternally expanding quantum foam that has bubbles form from quantum fluxuations, each of which gives birth to a local universe which exists independintly from all other daughter universes.

From a prospective of "outside" a daughter universe that is itself expanding, could you equally say that it's not expanding but rather getting less dense by its contents shrinking? Objects like a distant quasar would recede, but that apparent motion would come from the space between us becoming larger compared to our sizes. Put another way, outside a universe, would the universe look like a steady size or would the universe look like it was expanding into the foam stuff?

[uppi]

Originally Posted by contre

Put another way, outside a universe, would the universe look like a steady size or would the universe look like it was expanding into the foam stuff?

When you assume that the local universes are completely independent, they cannot expand into the foam, because then it would be possible for universes to overlap. We can only guess what would happen in such a collision but it would mean the independence is lost.

But as this is all hypothetical conjecture anyway, there is no reason to assume that they have to be completely independent. So if you allow (rare) collisions, the universes could also expand into the foam.


Or in other words: It all depends on how you build your multiverse.

[madviking]

How many of you guys have heard of the Mpemba effect?

[Mise]

Was discussing that with my (not so bright) friend on Facebook. This link seems to describe the possible causes much better than the wiki article: http://sasuke.econ.hc.keio.ac.jp/~ke...hot_water.html

[Samez]

Crazy stuff can happen with water. I once heard a lecture about pseudo structured liquid water. It was something about localized temporal structures (IIRC they were called islands or something like that and the structure was based on the polarity of the molecules) which can form in liquid water and are quite unstable. I could imagine they might somehow influence the crystallization.

[PlutonianEmpire]

http://news.yahoo.com/made-space-par...54.html?_esi=1

How exactly is 3D printing supposed to work? From what I can tell, it's creating new stuff out of basically nothing. Is this correct? I mean, where is the matter supposed to come from? Like, wouldn't creating it out of thin air make that phrase literal, in a sense, where you're taking air atoms and turning it into new components, and thus reduce vital air supply in the process?

Or am I missing something here?

[contre]

You're missing something.

3D printing works by layering 2D prints. Imagine a 3D object you wish to replicate. Divide it into thousands of paper-thin slices. Now "print" one of those paper-thin layers by mixing a bonding agent with a powder. Repeat this process for each cross section layer.