09:55 Jan 17, 2008 |
English language (monolingual) [PRO] Science - Astronomy & Space / Mercury exploration | |||||||
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| Selected response from: Attila Piróth France Local time: 11:35 | ||||||
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Discussion entries: 1 | |
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la sonde approchait la planète tous les deux ans (à intervalles de...) Explanation: La sonde Mariner 10 a pris ses photos à deux ans d'intervalle et donc dans les mêmes conditions d'éclairement, ce qui a permis de composer la mosaïque d'images présentée. |
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la sonde ayant croisé la planète tous les deux ans... Explanation: (NB: deux ans *mercuriens*) La sonde croise mercure à la même époque chaque fois, donc c'était toujours la même face qui était exposée (je suppose!) Example sentence(s):
Reference: http://www.astrosurf.com/saf/news/SAF2007/MANIF/COMMISSIONS/... |
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Physical explanation Explanation: For many years it was thought that Mercury was synchronously tidally locked with the Sun, rotating once for each orbit and keeping the same face directed towards the Sun at all times, in the same way that the same side of the Moon always faces the Earth. However, radar observations in 1965 proved that the planet has a 3:2 spin–orbit resonance, rotating three times for every two revolutions around the Sun... http://www.answers.com/Mercury?cat=technology&gwp=13 This means that the rotation of mercury is extremely slow; if the probe spends a couple of terrestrial hours or days in the vicinity of Mercury, the illuminated area will hardly change. Since the rotation and revolution of the planet show a perfect combined periodicity with a 2-year period, the probe will see the same when it returns 2 years later. If the probe approached the planet every year, it would see two different areas illuminated. |
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