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Space and Sky · entry 39 of 52
The first artificial satellite reached orbit in 1957 and transmitted a simple radio signal.
The longer version
The earliest satellite was a small metal sphere carrying antennas and a radio transmitter. Its beeping tone could be picked up by receivers around the world, which is how its orbit was tracked and its passage confirmed by listeners everywhere. It circled Earth repeatedly before its batteries failed.
That launch opened the space age and set off a rapid sequence of firsts: animals in orbit, humans in orbit, and probes to the Moon. It also established that objects placed in orbit stay there under gravity alone, circling the planet rather than flying away in a straight line. The signal also revealed conditions in the upper atmosphere.
Where this entry sits
The night sky looks calm, yet almost everything up there is moving, burning, or slowly changing. These facts cover planets, stars, the Moon, gravity, black holes, comets, and the story of how people began exploring beyond Earth. The full list sits on the Space and Sky page, where every entry is listed in order.
More From Space and Sky
Eight more entriesHumans first walked on the Moon in 1969 during a brief burst of exploration.
Read 41The Sun rotates faster at its equator than at its poles because it is gaseous.
Read 42Neutron stars pack more mass than the Sun into a sphere the size of a city.
Read 43White dwarfs are slowly cooling remnants of stars that once resembled our Sun.
Read 44Galaxies are moving apart as the space between them continues to expand.
Read 45The Andromeda Galaxy is the nearest large spiral galaxy and is drifting toward the Milky Way.
Read 46Star colors reveal surface temperature, with bluish stars hotter than reddish ones.
Read 47The Sun's corona is far hotter than its visible surface, for reasons still debated.
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