Pacific Ocean Indian Ocean
Question: How many oceans are there in the world ?
the Arctic Ocean
the Atlantic Ocean
the Pacific Ocean
the Indian Ocean
early navigational instruments
encyclopedia exploration celestial horizon equator overhead knot log nautical
magnetic random awkward reference precise portable accurate secure theoretical
Read about what navigation was like before modern instruments were used.
Sailing the oceans
Fast-reading How did seamen explore the oceans before latitude and longitude made it possible to plot a ship’s position?
? Keeping alongside the coastline ? Using celestial bodies天体
? Using wildlife
? Using the weather ? Using the sea
Using celestial bodies
to plot the positions to work out the latitude a special cloud formation indicates there is land close by
If seaweed was fresh and smelled strongly, the ship was close to land.
Sea birds could be used to show the way to land when it was nowhere to be seen.
Using the weather
To help identify the position of a stream or river when…
To direct their sailing
Use the information to analyze the navigational skills and write the answers in your own words.
1.To find the ship’s position at sea a the North Star and the sun. sailor used _______________________. 2.A sailor knew that land was nearby if clouds , fresh seaweed, he saw__________________________ nesting birds or fog __________________________.
currents or tides and 3.Sailors used sea ____________________ winds to increase their speed. ______
What skills did sailors use to explore the seas and discover new lands?
Using navigational instruments
1. Finding longitude the compass 2. Finding latitude ? the bearing circle
? the astrolabe (星盘) ? the quadrant (象限仪,四分仪) ? the sextant (六分仪)
Read again and fill in the blanks
There were two methods to find longitude: 1. __________________________ measuring time and speed
2.___________________________ compass and complicated
Read the passage (Reading) and decide whether the following statements are true (T) or false (F). 1. An early method of calculating longitude was to use a knotted rope tied to a log. T 2. The astrolabe was the first instrument to measure the sun’s position. F 3. The quadrant was more precise and simplified than the astrolabe, but still had its shortcoming. T
4. Up till now, the most accurate and reliable navigational instrument is the sextant. F 5. The astrolabe, quadrant and sextant are different kinds of navigational instruments and they have nothing to do with each other. F
3.Why are speed and time important in working out the longitude of a ship?
Because the earth moves fifteen
degrees westwards every hour. If you know your direction, speed and time, you can work out the approximate longitude or change in your position
in relation to the stars.
4. Why is the position of the sun and various stars useful for working out latitude?
Because they are fixed points in the sky and their movements in relation to the earth are already known. So they can be used to measure a ship's position.
5 Write down the working principles of the following instruments: Bearing circle: to compare the height of the sun now with the position of the sun at midday. Astrolabe: to compare the position of the ship in relation to some stars or the sun
Quadrant: a more precise form of the astrolabe, to measure how high
stars are above the horizon, and
compare that measurement with
previous measurements (using
the ship as one of the fixed
points to find its position)
Sextant: an updated version of the quadrant and so it was more accurate, to measure the angle between two fixed points outside the ship (using two mirrors to find the ship's position).
how We may want to know (1)____seamen explored the oceans(2)_______ before latitude appeared. (3)_______they didn’t have the Though modern navigational help, seamen could still control the sea by using some skills to explore seas and discover the new lands. (4)______ Using (use) nature is the first and most useful form of exploration (5)_________(explore), such as using celestial bodies, using wildlife, using the weather, and using the sea. Because of these skill, sailors increased the ability(6)__ to navigate new seas when they used instruments, (7)______ including (include) longitude and latitude.
1. We may well wonder how seamen explored the oceans before latitude and longitude made it possible to plot a ship’s position on a map.
may/might well 很可能，极有可能
These are excellent photographs and we may well use them in our magazine.
You might well find that you’ll need more by the weekend.
2. minimum (min) adj. 最小的, 最低的 n. 最小值, 最小化。 其反义词为maximum (max) adj. 最高的, 最多的, 最大极限的 n. 最大量, 最大限度, 极大
The minimum requirements for the job are a degree and two years’ experience. 该工作的最低要求是要有学位和两年 的工作经验。
You must get a minimum of 40 questions right to pass the examination.
3. There was no secure method of measuring longitude until the 17th century when the British solved this theoretical problem. secure adj.安全的, 可靠的, 放心的, 无虑的 v. 保护, 使安全 Our house is secure from flood. But Some measures are needed to secure the school from a flood.
security n.安全，保安，保护 Security was tight during the President’s visit. For security reasons the visitors were searched.
4.The compass has a special magnetic
pointer which always indicates the North
Pole, so it is used to help find the direction
that the ship needs to go.
magnetic adj. 磁的, 有磁性的, 有吸引力的
magnet n. 磁体, 磁铁
5. Then he could tell if he was sailing on his correct rather than a random course. random n. 随意, 任意 adj. 任意的, 随便的, 胡乱的 make a random choice 任意选择 at random = aimlessly; without any plan 随机，随便 This evening , the school leaders will
check students’ apparel at random.
6. It was awkward to use as one of the points of reference was the moving ship itself. awkward adj. 难使用的, 笨拙的, 尴尬的; 棘手的, 难处理的 There was an awkward silence, when no one knew what to say. An awkward situation arose during the peace talks.
1.Review new words. 2.Finish the Exx. of unit4 on the paper.