Tag: effects of light

At sunset or sunrise the suns rays have to pass through a larger distance in the atmosphere and most of the blue and other shorter wavelengths are remove by scattering.

To an astronaut it will appear as black.On earth we see the blue sky due to presence of atmosphere. Atmosphere refracts light ray coming from the sun and we see the colour of sky.In space, due to the absence of the atmosphere the light rays do not refract and reach the astronomer's eyes therefore it appears black.

Answer is D.
We cannot see through fog because of scattering.
Atoms and molecules in the air, including anything carried in the air like dust or smoke, will scatter light. Water droplets, as they are present in fog, also scatter light. The light falling on an object and reflected to a viewer can be scattered to heck and back before it gets to the place where it can be 'seen' by an observer. So the observer just sees a 'whiteout' instead of being able to make out anything beyond a few meters or so.

Answer is A.

Stars, except for the Sun, although they may be millions of miles in diameter, are very far away.  They appear as point sources even when viewed by telescopes.  The planets in our solar system, much smaller than stars, are closer and can be resolved as disks with a little bit of magnification. 
Since the Earth's atmosphere is turbulent, all images viewed up through it tend to 'swim.' The result of this is that sometimes a single point in object space gets mapped to two or more points in image space, and also sometimes a single point in object space does not get mapped into any point in image space.  When a star's single point in object space fails to map to at least one point in image space, the star seems to disappear temporarly.  This does not mean the star's light is lost for that moment.  It just means that it didn't get to your eye, it went somewhere else.
Since planets represent several points in object space, it is highly likely that one or more points in the planet's object space get mapped to a points in image space, and the planet's image never winks out.  Each individual ray is twinkling away as badly as any star, but when all of those individual rays are viewed together, the next effect is averaged out to something considerably steadier.
The result is that stars tend to twinkle, and planets do not.

The higher the wavelength the lesser the scattering. Yellow light has higher wavelength so it is least likely to be scattered among all colours in the visible region (except red & orange). So this light is visible from long distance even when there is foggy weather.

Among the constituent colours of white light, red has the longest wavelength and hence least frequency. As a result, red is least scattered among all colours. So, red colour reaches our eyes while all other colours scatter away during sun-rise and sun-set.

Red light is the least scattered by fine particles, fog or smoke present in the atmosphere which makes it easier to detect any danger clearly and distinctly.

A true solution does not have any fine particles dissolved in it which prevents scattering of light thus making it invisible.

The earths atmosphere is a heterogeneous mixture of minute particles like smoke, tiny water droplets, suspended particles of dust and molecules of air. When a beam of light strikes such fine particles, the path of the beam becomes visible. This phenomenon of scattering of light by the colloidal particles is called Tyndall effect.

The molecules of water and other fine particles in the atmosphere scatter light of shorter wavelengths at the blue end than light of longer wavelengths at the red end. Thus, when sunlight passes through water and air, the fine particles scatter the blue color more strongly than red. This scattered blue light enters our eyes and makes the ocean and sky appear blue. Near the horizon sunlight passes through thicker layers of air having larger particles that scatter light of longer wavelength such as the red end of the spectrum. Also it travels larger distance at horizon causing most of the light of shorter wavelength at the blue end of the spectrum to scatter away by the small particles of the atmosphere before reaching the earth.