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- How much lux does the Sun emit? - Physics Stack Exchange
When you look 'at the world' (i e to the horizon) on a clear day, unlesss the sun is at a very low angle, the surface of your eye is not illuminated directly by the sun, only reflected sunlight from the atmosphere, ground and objects The 32,000-100,000 lux figure is referring to a horizontal surface illuminated directly by the sun
- everyday life - Why do sunbeams diverge even though the sun is much . . .
The same applies to the beams of light above them The Sun is very far away and the beams are pretty much parallel, but they're pointing towards you, and perspective makes them appear to converge towards the vanishing point - which in this case is the Sun's location in the sky The technical term for these beams is "crepuscular rays "
- optics - If the sea surface were absolutely calm should the Sun . . .
As the elevation of the Sun decreases and it moves from the zenith to the horizon, the glitter becomes more and more elliptical, until it becomes a ribbon as in your image On the other hand, if the water were completely still, with a smooth and horizontal surface, then the sun glitter ribbon would be gone, and you would just see a direct
- astronomy - How big a coincidence is the Sun and Moon having almost . . .
Note that every moon with diameter i will block the sun in 201-i different orbits The smallest moon will block the sun in only one orbit, LEO The probability of a moon 2000 miles in diameter is thus $\frac{1}{200^2}$ that of the smallest moon Then the probability that a moon will block the sun is:
- sun - Nuclear fusion - Hydrogen isotopes - Physics Stack Exchange
The main fusion reaction in the sun is the proton-proton chain reaction, which takes six protons and produces two protons, one alpha particle, two anti-electrons, and two electron neutrinos The deuterium nucleus is only barely bound and can be destroyed — dissociated into a proton and neutron — by absorbing a gamma ray with energy more
- thermodynamics - Black and white matters. But why and how? - Physics . . .
The visible has about half of the energy coming from the sun on the surface, as seen in the link So a metal door in the sun will transfer the heat of the visible spectrum to the interior if painted black, will reflect it back and keep the interior cooler if painted white It is a good reason for painting roofs and walls white in hot countries
- temperature - How does water evaporate if it doesnt boil? - Physics . . .
When the sun is out after a rain, I can see what appears to be steam rising off a wooden bridge nearby I'm pretty sure this is water turning into a gas However, I thought water had to reach 100 degrees C to be able to turn into a gas Is there an edge case, for small amounts of water perhaps, that allows it to evaporate?
- astrophysics - Can Jupiter be ignited? - Physics Stack Exchange
It's fusing hydrogen into helium And it does this because it has so much mass that gravity is trying to collapse the star but the immense pressure means fusion takes place (creating an outward pressure to counteract the gravity pulling inwards creating a balance which must be maintained to keep the sun from collapsing inwards or exploding
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