Astronomy Picture of the Day . Noctilucent Clouds . ... Portuguese navigator Ferdinand Magellan and his crew had plenty of time to study the southern sky during the first circumnavigation of planet Earth. ... Is our Earth unique? In continuing efforts to answer this question, astronomers have now discovered an Earth-like planet orbiting a distant normal star. ... No sudden, sharp boundary marks the passage of day into night in this gorgeous view of ocean and clouds over our fair planet Earth. ...