why does an airplane flying at great altitude not cast a shadow on the earth?

well .. it is the same case

as y the pin does not cast a shadow on the wall when placed in front of the light

but im asking for the reason

I dn't think so , diffraction is valid iff the size of object is comparable with that of light .

My ans is this , even if a shadow is formed , the light coming from the surrounding areas are have more intensity and thus amt of light reaching that part is almost independent of the light blocked by the plane or bird.

Hope it's right. this is only a guess.

wll i think coz of diffraction may b correct ......!

but there hav a possiblity of formation of image.............!

distance of object from the screen(eg..earth surface) is very large so the image formed is very very diminshed .....................so we cannot see it ...............!

guess ...........correct me if i m wrong

A shadow is a region of darkness where light is blocked by an object. It occupies all of the space behind an opaque object with light in front of it. The cross section of a shadow is a two-dimensional silhouette, or reverse projection of the object blocking the light.

The closer to 90 degrees the angle between an elongated object and the direction of the light it blocks, the bigger its shadow. The smaller the angle between the direction of the light and the surface on which the shadow occurs, the longer the shadow is. If the object is close to the light source, the shadow is large.

For a non-point source of light, the shadow is divided into the umbra and penumbra. The wider the light source, the more blurred the shadow.

he further the distance from the object blocking the light to the surface of projection, the larger the silhouette (they are considered proportional). Also, if the object is moving, the shadow cast by the object will project an image with dimensions (length) expanding proportionally faster than the object's own length of movement. The increase of size and movement is also true if the distance between the object of interference and the light source are closer.

A shadow cast by the Earth on the Moon is a lunar eclipse. Conversely, a shadow cast by the Moon on the Earth is a solar eclipse.

On satellite imagery and aerial photographs, taken vertically, tall buildings can be recognized as such by their long shadows (if the photographs are not taken in the tropics around noon), while these also show more of the shape of these buildings.

A shadow shows, apart from distortion, the same image as the silhouette when looking at the object from the sun-side, hence the mirror image of the silhouette seen from the other side (see picture).

Shadow as a term is often used for any occlusion, not just those with respect to light. For example, a rain shadow is a dry area, which, with respect to the prevailing wind direction, is beyond a mountain range; the range is "blocking" water from crossing the area. An acoustic shadow can be created by terrain as well that will leave spots that can't easily hear sounds from a distance.

( from wiki )

this happens because the shadow is formed at some height above the surface of the earth.

if the plane flies very close to the surface,then its shadow can be seen.

 the umbra(dark region of the shadow) does not reach the surface when the plane is at a great height above the ground.

The bottom line is how close the object is to the screen ( here earth ) and how far is the light is ( here sun ).

oh , rohitkuruvila has already answered. Anyway the Q gave an excuse to search wiki.