Photo by Col. Chris Hadfield
A full sky aurora over Norway
Higher than the highest building, higher than the highest mountain, higher than the highest airplane, lies the realm of the aurora. Auroras rarely reach below 60 kilometers, and can range up to 1000 kilometers. Aurora light results from energetic electrons and protons striking molecules in the Earth’s atmosphere. Frequently, when viewed from space, a complete aurora will appear as a circle around one of the Earth’s magnetic poles. The above wide angle image, horizontally compressed, captured an unexpected auroral display that stretched across the sky over eastern Norway.
Image credit: Sebastian Voltmer
The Earth-like Mars
“Yet if hope has flown away
In a night, or in a day,
In a vision, or in none,
Is it therefore the less gone?
All that we see or seem
Is but a dream within a dream.”
“A Dream Within a Dream” (1849) by Edgar Allan Poe
Mars – a distant, extraterrestrial world, but it shares some surprising similarities with Earth. The rotation period is almost the same with 24 hours, 39 minutes and 21,67 seconds (as measured by astronomer William Herschel in 1777-1783), the planet possess an atmosphere and the surface shows periodic changes during a sequence of seasons.
First drawings of the Martian surface appeared in 1638, made by the Italian astronomer Francesco Fontana, and in 1645 the Dutch astronomer Christiaan Huygens produced the first “scientifically accurate” map, showing, so he believed, the large “hour glass”-ocean (today known as Syrtis Major, the southern highlands of Mars). In 1672 the Italian astronomer Giovanni Domenico Cassini (1625-1712) noted on the South Pole a white patch and in 1704/1719 a nephew of Cassini, Giacomo Filippo Maraldi (1665-1729), discovered also on the North Pole such a patch. It was William Herschel who suggested that these were polar ice caps and the extent of the glaciers varied during the Martian seasons. The melting polar ice caps suggested also that there was liquid water on Mars.
All the water on Earth would fit into a sphere 860 miles (1,385 km) wide.