76. Solar flares reach temperatures of 10 million °C and have the energy of a million atom bombs.
77. True binary stars are two stars held together by one another’s gravity, which spend their lives whirling around together like a pair of dancers.
78. Halley predicted that a comet he had discovered would return in 1758, 16 years after his death, and it really did. It was the first time a comet’s arrival had been predicted, and the comet was named after him as Halley’s Comet.
79. Ceres is the biggest asteroid in the Solar System – 940 km across, and 0.0002% the size of the earth.
80. The sun is about 5 billion years old and half a way through its life – as a medium sized star it will probably live for around 10 billion years.
81. Neptune’s mood Triton is the coldest place in the Solar System, with surface temperatures of -236°C.
82. Voyager 2 will beam back data until 2020 as it travels beyond the edges of the Solar System.
83. The Pioneer 10 and 11 probes carry metal plaques with messages for aliens telling them about us.
84. Einstein’s theory of Special Relativity (1905) shows that all measurements are relative, including time and speed. In other words, time and speed depends upon where you measure them.
85. When things are falling, their acceleration cancels out gravity, which is why astronauts in orbits are weightless.
86. The first space telescope was the Copernicus, sent out in 1972.
87. Astronauts learn Scuba diving which helps them to deal with space walks.
88. Weightlessness makes astronauts grow several centimeters during a long mission.
89. The first living creature in space was the dog Laika on – board Sputnik 2 in 1957. Sadly, she died when the spacecraft’s oxygen supply ran out.
90. The first manned space flight was made in April 1961 by the Soviet Cosmonaut, Yuri Gagarin in Vostok 1.
91. The heart of a star reaches 16 million °C. A grain of sand this hot would kill someone 150 km away.
92. Stars twinkle because we see them through the wafting of the atmosphere.
93. The sun weighs 2,000 trillion trillion tones – about 300,000 times as much as the Earth – even though it is made almost entirely of hydrogen and helium, the lightest gases in the Universe.
94. The sun gets hot because it is so big that the pressure in its core is so tremendous – enough to force the nuclei of hydrogen atoms to fuse to make helium atoms. This nuclear reaction is like a gigantic atom bomb and it releases huge amounts of heat.
95. The nuclear fusion reactions in the Sun’s core send out billions of light photons every minute but they take 10 million years to reach its surface.
96. The Hiroshima bombs released 84 trillion joules of energy. A supernova releases 125,000 trillion trillion times as such.
97. The most distant galaxies (quasars) have red shifts so big that they must be moving away from us at speeds approaching the speed of light.
98. When light waves from distant galaxies are stretched out his way, they look redder. This is called red shift.
99. The moon’s gravity is 17% of the Earth’s so astronauts in space suits can jump 4 m high on the moon.
100. The moon is the only other world that humans have set foot on. Because the moon has no atmosphere or wind, the footprints planted in its dusty surface in 1969 by the Apollo astronauts are still there today, perfectly preserved.