Question

What adjustment has to be made when ships cross the International Date Line?
OR
Explain why a day appears to be lost in sailing round the world from east to west and gained when travelling from west to east.

Answer 1

The earth rotates on its axis from west to east, hence places in the east have their sunrise earlier than places in the west. Now if a man travels around the world from east to west, for every degree of longitude covered; he will have to set back his watch by four minutes. Thus after covering 360°when he returns to the place from where he started he will have to set back his watch 360 x 4 / 60 = 24 hrs. Thus he will appear to have lost a day. When Francis Drake returned to England after circumnavigating the globe, he thought it was Saturday, whereas actually it was Sunday. The reason was that he had traveled from east to west, and had under calculated a day. On the other hand, if a man travels from west to east, for every degree of longitude covered he will put forward his watch by four minutes and for 360° he will forward it 24 hrs. When he returns to the place from where he started he will appear to have gained a day. When Cap. Basil Hailed reached Manila after circumnavigating the globe, he thought it was Monday; whereas actually it was Sunday. The reason was that he had traveled from west to east and had over calculated a day.