the dark part of a shadow where light from a source is completely blocked is called the penumbra.
the dark part of a shadow where light from a source is completely blocked is called the penumbra.
the dark part of a shadow where light from a source is completely blocked is called the?
penumbra
the umbra (latin for "shadow") is the innermost and darkest part of a shadow, where the light source is completely blocked by the occluding body. an observer in the umbra experiences a total eclipse. the umbra of a round body occluding a round light source forms a right circular cone; to a viewer at the cone's apex, the two bodies are equal in apparent size. the distance from the moon to the apex of its umbra is roughly equal to that between the moon and earth (). since earth's diameter is 3.70 times the moon's, its umbra extends correspondingly farther: roughly .
umbra, penumbra and antumbra
tathavade or santoshgad hill fort (phaltan t; 17� 57' n, 74� 20' e; rs. lonand, 2.9 m.) lies in the north-west corner of the phaltan taluka, about 12 miles south-west of phaltan, the taluka headquarters! the fort is now easily approachable throughout the year as the public works department has recently constructed a pucca road from village tathavade lying at the foot of the hill. the fort is roughly triangular in shape. the hill on which it stands is a little lower than the main range. the apices of the triangle are north-west and south-east making it nearly equilateral. at the foot on the northern side lies the village of tathavade (p. 1,001) with people nearly all cultivators mostly ramoshis and marathas. the defences consist of three walls, the top wall going all round the hill and forming what may be called the citadel. it surmounts a perpendicular scarp of black rock about thirty feet high, and is itself about fifteen feet higher. in thickness it is twenty feet and had originally a parapet about six feet high and three feet thick, all of which has broken down. it is made of laterite blocks from one or two cubic feet each, and solidly set in mortar, lined with small stones and mud. it is carefully provided at intervals with secret escape doors for the garrison should the fort be successfully taken. it is especially strong at the three angles from which project triangular outworks about sixty feet lower than the citadel. the outworks are of unequal size, but built of the same materials and more strongly even than the citadel. the sides of the south-west out-work are not more than thirty yards long but it is perhaps the most solid of the three; the sides of the north-east outwork are about fifty yards, and those of the north-west out-work about seventy yards long. the first two out-works communicated with the citadel by a small door not more than two feet wide built through the walls, which led on to the steps cut in the scarp. the citadel wall has a gap at the north-west angle which formed the communication with the north-west out-work. on the north-east side of this was the main gateway about five feet wide, also made of laterite, of beautifully cut massive masonry. it faced, and was sheltered by a projecting bastion. the north side of the hill was partly protected for about a hundred feet by two lower walls or terraces, the one below the other with bastions at intervals. they are of much lighter workmanship than the blocks in rough mortar and the lining of uncut stones and mud. these walls both run east and west along the entire length of the northern face of the hill. they then turn through an angle of over 90 degrees, and are taken up the hill to meet the walls above them. the upper of the two is broken by a gateway of trap facing east, like the upper gateway, similarly sheltered, and otherwise like it, but of far less strength and of much rougher workmanship. the lowest wall is divided by a gap of full thirty feet in the centre flanked by two strong bastions, but no gateway. the ascent between these three entrances and from the north-west out-work on to the citadel is by a winding path with steps at intervals where, not unfrequently, the naked scarp of the rock has to be surmounted. the steps are nearly everywhere broken down and the way generally blocked with prickly pear. the above description will show that the hill was unprotected below the citadel and its out-works on the south-west and south-east sides, and that elaborate care was taken to protect the north side. there seems to be no special reason for this difference except that the entrance and therefore the weakest point of the citadel was on the north side. by making the two gateways face east and protecting them with projections of the wall, their assault was impeded while it was impossible to hit them directly with cannon shot from the plain below, which, according to tradition, was a special point in the fortification of the day. in sieges it was apparently the fashion to direct a cannonade first against the gate and to provide a force to rush through if the besiegers succeeded in bursting it. the difficulties of elsewhere penetrating or escalading hill forts such as these, were probably and not wrongly thought insuperable, bribery and stratagem apart. the citadel is not more than 600 yards round and its area not much more than twenty acres. there were originally but few buildings. the headquarters or sadar was a building about fifty feet by thirty feet including its two otas or verandahs. it opened to the north and besides accommodating the treasury, was used as a sort of court-house for the subhedar in charge of the fort. next to it on the west was a stone building about forty feet by twenty, with walls three feet thick, and a roof on the south side made of brick coated with cement. it contained three chambers for storage of grain, treasure and gunpowder. the east chamber still remains. immediately south of the east chamber is the great pond, cut some sixty to seventy feet down into the rock, and the sides smoothed off with great care. it holds a tolerable supply of water, but is fed by no spring. it is about twenty-five to thirty feet square and has steps on the eastern side leading down to the water's edge. halfway down at a landing and turn of the steps is a small temple of tatoba mahadev from whom the fort takes its name. this large pond was apparently the only source of the water-supply of the citadel. it has been much choked with silt, and is said to hold much less water than before, much probably leaking down through the laterite. the rest of the citadel is so blocked with prickly pear that no other buildings can be distinguished. the hill top has room only for very few. one is a mosque for musalmans. the north-east out-work has some buildings while, inside the two lower walls, are others all in ruins. outside the lowest entrance is pointed out the side of the elephant-house, fit for not more than two beasts. on the saddle back between the southern angle and the main range of hills has been cut a gap with remains of buildings said to have been the grass stacks of the fort. the grass was supplied chiefly from lands on the plateau above the mahadev range and brought for storage to this spot. it is more than two hundred yards from the fort and is hardly convenient than the village itself which is at least as accessible as the fort. immediately inside and directely facing the lowest entrance is a large cave pond. its mouth has been almost wholly blocked with rubbish. a descent of some six feet is therefore necessary to reach the water. the excavation is partly natural but evidently enlarged artificially. the exact size of the cave pond cannot be made out. three massive pillars appear supporting the roof. the rock is laterite and hence no doubt the abundant supply of excellent water filters from above. the upper fort is nearly all made of laterite with no traces of quarrying about. it seems therefore not improbable that the ponds were excavated by the fort builders and the stone used for the fort walls. there are four other similar ponds completely blocked up. their stone and that of the big pond on the top would amply suffice for the external work considerable as it is. the mildew of this laterite is used by the people as a tonic for women after child-birth. it probably contains some principle of iron. it is a belief in the village that the large pond in the citadel and this cave pond are connected by a passage now choked up, and that a lemon thrown into the water of the one used in former times to appear on the surface of the other. these ponds show that the hill internally is made of laterite with an outer coating of trap, thin at the sides but on the top some forty feet thick.
santoshgad