# Tag Info

1

This presents the same problem as your previous question: Determine the number of days with North-East wind direction from the number of days with North and East wind direction? If we know the wind was from the North on $a$ days and from the North-East on $b$ days then there is no way to tell how many days the wind was from the NNE. The best you could do is ...

1

Generally speaking there will be some correlation between wind directions. For example if on some specific day the wind blows from the North or East it is quite likely there was a North-East wind in the week or so around that day. By contrast if the wind is from the South-West on a particular day it is less likely there was a North-East wind in the week or ...

-5

I don't think it makes sense to talk about a temperature with regard to Aurora effects. It's an epiphenomenon. It's almost like asking "how fast is a car engine moving?" wholly dependent on your frame of reference. In this case the difficulty is using the term "temperature", which is too tied to perception to differentiate a purely physical answer.

5

A quick google search for "aurora plasma temperature" brings up several interesting results, which seem fond of reporting temperatures in electron volts. That's entirely sensible, but probably not quite what you want. While we could do some math to convert those measurements to Kelvin, Rocket measurements of plasma densities and temperatures in visual aurora ...

1

If you know when to expect it, light can be detected at the single photon level. For very long distances, the expected photon flux will be less than one per detector per unit time of your choice. Go look up the Lunar Laser Ranging Experiment, in which light was detected at this level. Also, the Lunar Laser Communication Demonstration, which allows high ...

6

Infinity as long as you have a detector strong enough to detect it. Light keeps on travelling in a straight line forever as long as it doesn't bounce off some object. The problem with the lights you are talking about is that their intensity is really low and you can't resolve them because of the other stronger sources of lights you have around yourself. ...

-1

any flow is driven by pressure gradient, which must overcome the friction of flow through the tube. It's a very long way, hence huge pressure drop relative to the initial pressure gradient. No flow

4

Assuming the tube is insulated along its whole length (which I think is the intent of the question although it's not stated), I think a flow in either direction is stable and sustaining, but there is no particular reason it will form in either direction if the initial conditions are that the air in the tube is still. It will then depend on the average air ...

1

I think you've got the whole reason. We have good evidence that meteor showers are caused by lots of tiny pieces of fluffy comet detritus, which has no chance of reaching the ground; a bright bolide, however, is much more likely to have a substantial rocky or metallic mass.

4

You can rearrange the terms to have any constant as the base of the exponent: $D = 1.25 e^{(-0.0001h)}$ $= 1.25 (e^{0.0001})^{-h}$ $= 1.25 (2^{\frac{0.0001}{ln 2}})^{-h}$ $\approx 1.25 (2^{0.00014})^{-h}$ $= 1.25 \times 2^{(-0.00014h)}$

10

It's actually a surprisingly straightforward differential equation. If you assume that the acceleration due to gravity $g$ doesn't change with altitude (a good approximation if the atmosphere is thin compared to the radius of the earth), Bernoulli's relation tells you the change in the pressure $P$ with height $h$: $$\frac{dP}{dh} = -\rho g$$ Meanwhile the ...

3

Euler's constant appears naturally in phenomena where the spatial gradient of a quantity (or rate of change with time) is proportional to the quantity itself: $$\frac{\mathrm{d}X}{\mathrm{d}x} = X/x_0$$ ($x_0$ determines the strength of the proportionality, and keeps units straight.) The solution of this differential equation is $$X=X_o e^{x/x_0}$$ $X_0$ ...

1

I just wanted this to be a comment, but it got too long. Sorry if it's too obscure. This addresses why the sky seems like it has a solid blueish colour, and why moon does not have a bright day. Since as of no answer mentions it I just wanted to say, that the effect "responsible" for the blue sky is called Rayleigh scattering. "Technically" it's a ...

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