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The point in a planet’s orbit where it is
farthest from its orbital focus, generally
a star. At its aphelion, Earth is
94.5 million miles from the sun.
The outermost shell of a planet or
satellite. On Earth, the lithosphere
is the rocky crust and upper mantle,
divided into tectonic plates.
Derived from the Greek Oceanus, the ocean composes
much of a planet’s hydrosphere. Oceans of saline water
cover 71 percent of Earth’s surface. Extraterrestrial
oceans may be composed of water or other compounds.
SOME KEY WORDS ON THE THEME OF EARTH
500,000 SMALLER ORBITAL DEBRIS (less than 10 cm in diameter)
& 21,000 LARGER BITS (larger than 10 cm)
THERE ARE 1,100 ACTIVE SATELLITES &
ABOUT 2,600 INAC TIVE.
THE ONLY NATURAL SATELLITE IS THE MOON.
The oldest man-made space object still in orbit is Vanguard 1, launched
by the U.S. into medium Earth orbit in 1958. It was the fourth artificial
satellite ever launched, behind a pair of Sputniks and Explorer 1.
Now operated by SES World Skies, the commercial geosynchronous satellites
of the AMC fleet provide telecom services around the world. The latest
launch, AMC- 21, is located at 125 degrees West longitude and broadcasts
signals to Canada, the Caribbean, Mexico, and the United States.
The Landsat missions from the U.S. Department of Interior, NASA, and the Department of
Agriculture began in 1972 to provide images of the Earth. Landsat 5, launched in 1985,
set a Guinness World Record for the longest operating Earth observation satellite with a
mission of 28 years and 10 months. The next Landsat, Landsat 9, is set for launch in 2020.
WHAT'S THAT UP IN THE SKY?