Earth

Describe any three experiments or observations which support the belief that the earth is roughly a sphere. (150 Words)

Simple and Straight observations:
Observation of an approaching ship: When we view an approaching ship we first observe the appearance of its highest portion, i.e., the mast, then funnel and lastly the deck. Had the Earth been flat, we would have seen the whole ship in the first instant. If Mast of ship is seen from all direction from a fixed point, we can calculate the curvature of the Earth.
Shadow of the Earth: At the time of lunar eclipse the shadow of the Earth that falls on the Moon is round. More specifically the edge of the shadow is an arc of a circle. The Moon, as seen from the Earth, looks like a flat disk. It can be proved with the help of geometry that only a sphere will cast a circular shadow on a flat surface.
Sun rise: The sun rises first in the East and appears later in the west. Had the Earth been flat, the sun would have risen in the East and West at the same time.
Thus, Earth is roughly a sphere.
Explain why daylight increases as we go pole wards in summer in the northern hemisphere. Also explain the effect of latitude on the length of the day and night.  (150 Words)
Earth moves in space has two types of movements in space,
* Rotation around its own axis
* Revolution around the sun
These two movements clubbed with the inclined position of earth’s axis of rotation with elliptical place of earth leads to variation in the length of day and nights all over the globe.
As the earth axis makes an angle of 66 1/2 degrees with the plane of elliptic, during the month of June when it is summer over the northern hemisphere, the sun rays directly fall on the tropic of cancer. So this leads to longer days and shorter nights in the northern hemisphere area leading to increase in the day light as well. In fact at the poles the daylight persists for almost 6 months without any sunset till onset of winter.
Length of day and night does vary according to the season and latitudinal position. At the equator the day and night are mostly of same lengths all-round the year. As we go poll wards either one of them becomes longer. Example during the summer in northern hemisphere, length of daytime increases as we go towards poles, and at same time as we move southwards towards Antarctic, the length of night time increases and at the south pole it would be completely dark for 6 months without day light.