Alex Cunningham

cwnl:

Comet vs. Our Sun

Comet colliding with the Sun coincides with a coronal mass ejection. Image from the NASA SOHO Observatory.

(via ikenbot)

Green flashes and green rays are optical phenomena that occur shortly after sunset or before sunrise, when a green spot is visible, usually for no more than a second or two, above the sun, or a green ray shoots up from the sunset point. […]

The reason for a green flash lies in refraction of light (as in a prism) in the atmosphere: light moves more slowly in the lower, denser air than in the thinner air above, so sunlight rays follow paths that curve slightly, in the same direction as the curvature of the Earth. Higher frequency light (green/blue) curves more than lower frequency light (red/orange), so green/blue rays from the upper limb of the setting sun remain visible after the red rays are obstructed by the curvature of the earth.

Green flashes are enhanced by mirage, which increase the density gradient in the atmosphere, and therefore increase refraction. A green flash is more likely to be seen in clear air, when more of the light from the setting sun reaches the observer without being scattered. We might expect to see a blue flash, but the blue is preferentially scattered out of our line of sight and remaining light ends up looking green.

With slight magnification a green rim on the top limb of the solar disk can be seen on most clear-day sunsets. However the flash or ray effects require a stronger layering of the atmosphere and a mirage which serves to magnify the green for a fraction of a second to a couple of seconds.

There are problems with the explanation of the cause of the green flash. The refractive index of air is 1.0003 compared with about 1.5 for glass, which means that a ray of light will suffer little refraction in the atmosphere, i.e. the ray will continue in almost the same direction as that before encountering the atmosphere. Further, there is the question of why the flash is of such a small area considering the size of the sun’s image. There are many unanswered questions relating to this phenomenon. […]  (via wikipedia- green flash)