X-Ray Moon

X-Ray Moon



This x-ray image of the Moonwas made by the orbitin ROSAT Röntgensatellit) Observatory in 1990.In this digital picture, pixel brightness corresponds to x-ray intensity.Consider the image in three parts:the bright hemisphere of the x-ray moon,the darker half of the moon,and the x-ray sky background.The bright lunar hemisphere shine in x-rays because it scattersx-rays emitted by the sun.The background sky has an x-rayglow in part due tothe myriad of distant, powerful active galaxies, unresolvedin the ROSAT picture but recently detected in Chandra Observator x-ray images.But why isn't the dark half of the moon completely dark NewChandra results also suggest that a few x-rays only seemto come from the shadowedlunar hemisphere.Instead, theyoriginate in Earth's geocorona o extendedatmosphere which surrounds the orbiting x-ray observatories.

Cold Comet Halley

Cold Comet Halley



While this may not be the most esthetic image o Comet Halleythat you have ever seen, it is likely the most unique.The tiny cluster of pixels circled is th famouscomet along its orbit over4 billion (4,000,000,000) kilometers or 2 AUfrom the Sun - a record distance for a comet observation.Its last passage throug our neck of the woods in 1986 Comet Halleypresently cruises through the dim reaches of the outer solarsystem, almost as far away as outermost gas giant Neptune, and shows nosign of activity.Captured in March, this negative image is a composite ofdigital exposures made with threeof ESO's Very Large Telescopes.The exposures are registered on th moving comet, so thepicture shows background stars and galaxies as elongated smudges.An earth-orbiting satellite appears as a dark streak at the top CometHalley is clearly extremely faint here, but large earthboundtelescopes will be able to followit as it grows fainter still, reachingthe most distant point in its orbit, more than 5 billion kilometers(35 AU) from the Sun, in 2023.

Reflections on the 1970s

Reflections on the 1970s



The 1970s areoften overlooked.In particular, the beautiful grouping of reflection nebula NGC 1977,NGC 1975, and NGC 1973 in Orion areoften overlooked in favor ofthe substantial stellar nursery better known as the Orion Nebula.Found along the sword of Orion just nort of thebright Orion Nebula complex, these nebulae are also associate with Orion's giantmolecular cloud which lies abou 1,500 light-years away, butare dominated by the characteristic blue color of interstellardust reflecting light from hot young stars.In this sharpcolor image a portion of the Orion Nebula appearsalong the bottom border with the cluste of reflection nebulaeat picture center.NGC 1977 stretches across the field just below center,separated from NGC 1973 (above right) and NGC 1975 (above left)by dark regions laced with faint red emission fromhydrogen atoms.Taken together, the dark regions suggest to many theshape of a running man.

An Unusual Event Over South Wales

An Unusual Event Over South Wales



Jon Burnett, a teenager from South Wales, UK, was photographing some friends skateboarding last week when the sky did something very strange. By diverting his camera, he was able to document this rare sky event and capture one of the more spectacular sky images yet recorded. Roughly four minutes later, he took another picture of the dispersing trail. What is it? Experts disagree. The first guess wasa sofa-sized rock that exploded as a daytime fireball, but perhaps a better hypothesis is an unusual airplane contrail reflecting the setting Sun Bright fireballs occur over someplace on Earth nearly every day. A separate bolide, likely even more dramatic, struck India only a few days ago. Editor's note: The APOD text was updated on Oct. 1.