There's something behind these clouds. Those faint graceful arcs, upon inspection, are actually far, far in the distance. They are the Earth's Moon and the planet Venus. Both the Moon and Venus are bright enough to be seen during the day, and both are quite capable of showing a crescent phase. To see Venus, which appears quite small, in a crescent phase requires binoculars or a telescope. In the above dramatic daytime image taken from Budapest, Hungary, the Moon and Venus shared a similar crescent phase a few minutes before the Moon eclipsed the larger but more distant world. About an hour later, Venus reappeared.
Explanation: What if you saw your shadow on Mars and it wasn't human? Then you might be the Opportunity rover currently exploring Mars. Opportunity and sister robot Spirit have been probing the red planet since early 2004, finding evidence of ancient water, and sending breathtaking images across the inner Solar System. Pictured above, Opportunity looks opposite the Sun into Endurance Crater and sees its own shadow. Two wheels are visible on the lower left and right, while the floor and walls of the unusual crater are visible in the background. Opportunity and Spirit have now spent over three years exploring the red world, find new clues into the wet ancient past of our Solar System's second most habitable planet.
Triton: Neptune's Largest Moon
Credit: Voyager 2, NASA
Explanation: In October of 1846, William Lassell was observing the newly discovered planet Neptune. He was attempting to confirm his observation, made just the previous week, that Neptune had a ring. But this time he discovered that Neptune had a satellite as well. Lassell soon proved that the ring was a product of his new telescope's distortion, but the satellite Triton remained. The above picture of Triton was taken in 1989 by the only spacecraft ever to pass Triton: Voyager 2. Voyager 2 found fascinating terrain, a thin atmosphere, and even evidence for ice volcanoes on this world of peculiar orbit and spin. Ironically, Voyager 2 also confirmed the existence of complete thin rings around Neptune - but these would have been quite invisible to Lassell!
This infrared image from NASA's Spitzer Space Telescope shows the Rosette Nebula, a pretty star-forming region more than 5,000 light-years away in the constellation Monoceros. In optical light, the nebula looks like a rosebud, or the "rosette" adornments that date back to antiquity.
Lurking inside this delicate cosmic rosebud are so-called planetary "danger zones," surround super hot stars, called O-stars (blue stars inside spheres), which give off intense winds and radiation. Young, cooler stars that happen to reside within one of these zones are in danger of having their dusty planet-forming materials stripped away.
While scientists have known about O-star danger zones, their parameters were among science's mysteries. Astronomers used Spitzer's infrared vision to survey the extent of the five danger zones shown here. The results showed that young stars lying beyond 1.6 light-years, or 10 trillion miles, of any O-stars are safe, while those within this zone are likely to have their potential planets blasted into space.
Radiation and winds from the super hot stars have collectively blown layers of dust (green) and gas away, revealing the cavity of cooler dust (red). The largest two blue stars in this picture are in the foreground, and not in the nebula itself.
Image credit: NASA/JPL-Caltech/Univ.of Ariz.
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