# Tag Info

## New answers tagged sun

4

A brief history of what science thought about the sun can be found here . It is reasonable that once thermodynamics advanced to the point of measuring and calculating energies the discrepancy between heat output of the sun and the age of the earth had to be explained. They tried with gravitation, but until the discovery of nuclear energy and E=m*c^2 it ...

0

And why more toward yellow than green? Human vision and perception of colors is a complex process. It is safe to say humans are not very good at determining the actual spectral distribution of light they see. The sunlight may very well have frequency distribution that has maximum in green and humans may still see it as having different coloration. That ...

-1

Note the vertical scale on the two graphs you gave: The solar spectrum at sea level is given as an intensity (power per area), and it is very nearly flat over most of the visual range. The eye sensitivity is given as a percentage, which the wikipedia page where it is used does not explain beyond calling it "normalized" and "relative brightness sensitivity." ...

0

A great amount of planetary data is available at this NASA website. There doesn't appear to be a strong correlation, but you could use this NASA data to do the statistics.

13

(edited version. My thanks to Rob for clearing up my misunderstandings) As dmckee writes, weak interactions between DM particles and baryons are necessary to capture dark matter, otherwise particles that enter the solar system would simply move through it and eventually leave it again. More specifically, the local rms velocity of DM particles is commonly ...

1

Your number of 100km/s might be true for the "average speed", but probably way off for the "root mean square" speed. Dark matter can be - on average - orbiting the galactic potential with everything else, however individual WIMPS will be of much higher velocity, thus making the $v_{rms}$ very high. (this high speed follows from the standard assumptions on ...

15

Well, like anything else that comes in from distant parts it's going out again without a either a three-body momentum transfer or some kind of a non-gravitational interaction. If you assume a weakly interacting form of dark matter, then I think the answer has to be yes, but the rate is presumably throttled by the weak interaction cross-section of your ...

0

they are 3 ways to exchange heat : conduction, convection, and radiation. When we touch an object, the heat is transferred from the hot body to the cold body thanks to electrons collisions within the mediums. The speed at which this heat is transferred depends on the thermal conductivity. The convection is a similar process that involves matter like air ...

1

In a physics lab there is a (more or less) unambiguous definition of the word heat. In a pub there is not. In general usage, the word can mean different things. For example, it might mean "thermal energy". It might mean "thermal energy transfered by conduction". It might mean "infrared radiation". From context, I think you have taken the second of ...

1

As the moon is continually receding from the earth due to the tides, the end result will be a stable orbit. about 2.3 billion years from now, the increase of the Sun's radiation will have caused the Earth's oceans to vaporize,[13] removing the bulk of the tidal friction and acceleration. The orbit should be stable. But the sun will finally become a ...

0

The Sun will collide with the Earth. The orbits are stable. But in about 5 billion years, the Sun will run low on hydrogen and begin burning helium. This will make it expand and engulf the Earth.

2

32,000 - 100,000 lux is the typical range of illumination that the Sun provides. You don't have to look at the sun, you look at the world it illuminates. Lux is a "per unit area" quantity - not a "per solid angle" quantity. The variation in values mostly depends on the position of the sun in the sky - when it is low, there is significant scatter of sunlight ...

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