Answer to Question 1
C
Answer to Question 2
Numerous methods exist to study currents. Surface currents can be traced with drift bottles or drift cards, which are useful in determining coastal circulation. However, these tools provide no information on the path the drift bottle or card may have taken between its release and collection points. Researchers who want to know the precise track taken by a drifting object can deploy more elaborate devices, such as buoy arrangements, which can be tracked continuously by radio direction finders or radar. A newer class of autonomous research tools has also been developed. The Slocum is a glider that flies up and down through the water column powered by gravity and buoyancy. Fleets of these gliders map the ocean's thermohaline depth profiles, chlorophyll content, and other parameters for years and, on their occasional visits to the surface, transmit data to satellites. Another tool is the Argo system of floats, which move vertically in the water column. The floats return to the surface once every 10 days, measuring temperature and conductivity as they move. Data are uploaded to satellites and used to calculate salinity.
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The Sun as it appears from the surface of Earth during the middle of the day
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Earth as viewed from Lunar orbit during the Apollo 8 mission, Christmas Eve, 1968. Africa is at the
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