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WonderSpace fact

Venus takes 243 Earth days to rotate once relative to the stars, longer than its 225-day orbit around the Sun. It also spins backwards compared with most planets, so on Venus the Sun would rise in the west.

NASA

Science

The story behind the card

The 243-day figure is Venus's sidereal rotation period, measured against the distant stars. Because Venus spins backwards while it moves around the Sun, a solar day, from one local noon to the next, lasts about 117 Earth days. So 'a day on Venus' can mean 243 or 117 Earth days, depending on what is being measured. Someone on the surface would see the Sun rise in the west and set in the east about 58 Earth days later, if the thick clouds ever let it through. Why Venus turns so slowly, and backwards, is still debated. It probably formed spinning differently. Over billions of years the Sun's gravity, which tends to slow a planet's spin, and tides raised in its thick, sun-heated atmosphere may have brought it to the slow backward turn seen today.

Türkçe oku
Venüs, yıldızlara göre kendi ekseni çevresindeki bir turunu 243 Dünya gününde tamamlar; Güneş'in çevresini ise 225 günde dolaşır. Üstelik çoğu gezegene göre ters yönde döner; bu yüzden Venüs'te Güneş batıdan doğar.

243 günlük süre, Venüs'ün uzak yıldızlara göre ölçülen dönüş süresidir. Venüs, Güneş'in çevresinde ilerlerken ters yönde döndüğü için bir güneş günü, yani bir öğleden ötekine geçen süre, yaklaşık 117 Dünya günüdür. Dolayısıyla “Venüs'te bir gün”, neyin ölçüldüğüne göre 243 ya da 117 Dünya günü demek olabilir. Yüzeydeki biri, kalın bulutlar izin verseydi, Güneş'in batıdan doğduğunu ve yaklaşık 58 Dünya günü sonra doğuda battığını görürdü. Venüs'ün neden bu kadar yavaş ve ters yönde döndüğü hâlâ tartışılıyor. Gezegen büyük olasılıkla farklı bir dönüşle oluştu. Güneş'in çekimi bir gezegenin dönüşünü yavaşlatma eğilimindedir; Güneş'in ısıttığı yoğun atmosferde oluşan gelgitler de dönüşü etkiler. Milyarlarca yıl içinde bu iki etki, Venüs'ü bugünkü yavaş ve ters dönüşüne getirmiş olabilir.

Sources and further reading

Background reading: Venus
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