Free Republic

Explanation: What created this great arc in space? This arcing, graceful structure is actually a bow shock about half a light-year across, created as the wind from young star LL Orionis collides with the Orion Nebula flow. Adrift in Orion's stellar nursery and still in its formative years, variable star LL Orionis produces a wind more energetic than the wind from our own middle-aged sun. As the fast stellar wind runs into slow moving gas a shock front is formed, analogous to the bow wave of a boat moving through water or a plane traveling at supersonic speed. The slower...

Explanation: In this early May night skyscape, a mountain road near Bursa, Turkey seems to lead toward bright planets Mars and Saturn and the center of our Milky Way Galaxy, a direction nearly opposite the Sun in planet Earth's sky. The brightest celestial beacon on the scene, Mars, reaches its opposition tonight and Saturn in early June. Both will remain nearly opposite the Sun, up all night and close to Earth for the coming weeks, so the time is right for good telescopic viewing. Mars and Saturn form the tight celestial triangle with red giant star Antares just right of...

Explanation: On May 9, innermost planet Mercury crossed IN FRONT of the Sun. Though pictures project the event in only two dimensions, a remarkable three dimensional perspective on the transit is possible by free viewing this stereo pair. The images were made 23 minutes apart and rotated so that Mercury's position shifts horizontally between the two. As a result, Mercury's orbital motion produced an exaggerated parallax simulating binocular vision. Between the two exposures, the appropriately named planet's speedy 47.4 kilometer per second orbital velocity actually carried it over 65,000 kilometers. Taken first, the left image is intended for the right...

Explanation: An enhanced-color view, this image covers a 350 by 750 kilometer swath across the surface of Jupiter's tantalizing moon Europa. The close-up combines high-resolution image data with lower resolution color data from observations made in 1998 by the Galileo spacecraft. Smooth ice plains, long fractures, and jumbled blocks of chaos terrain are thought to hide a deep ocean of salty liquid water beneath. Though the ice-covered alien ocean world is outside the Solar System's habitable zone, new studies show the potential chemistry driving its oxygen and hydrogen production, a key indicator of the energy available for life, could produce...

Explanation: Influenced by the strong Pacific El Nino, cloudy skies have more often come to Chile's high Atacama Desert this season, despite its reputation as an astronomer's paradise. Located in one of the driest, darkest places on planet Earth, domes of the region's twin 6.5 meter Magellan telescopes of Carnegie Las Campanas Observatory were closed on May 13. Still, a first quarter Moon and bright stars shine through in this panoramic night skyscape, the lunar disk surrounded by a beautiful, bright halo. The angular radius of the halo is 22 degrees. Not determined by the brightness or phase of the...

Explanation: The Great Nebula in Orion is a colorful place. Visible to the unaided eye, it appears as a small fuzzy patch in the constellation of Orion. Long exposure, multi-wavelength images like this, however, show the Orion Nebula to be a busy neighborhood of young stars, hot gas, and dark dust. This digital composite features not only three colors of visible light but four colors of infrared light taken by NASA's orbiting Spitzer Space Telescope as well. The power behind much of the Orion Nebula (M42) is the Trapezium - four of the brightest stars in the nebula. Many of...

Explanation: What forms lurk in the mists of the Carina Nebula? The dark ominous figures are actually molecular clouds, knots of molecular gas and dust so thick they have become opaque. In comparison, however, these clouds are typically much less dense than Earth's atmosphere. Featured here is a detailed image of the core of the Carina Nebula, a part where both dark and colorful clouds of gas and dust are particularly prominent. The image was captured last month from Siding Spring Observatory in Australia. Although the nebula is predominantly composed of hydrogen gas -- here colored green, the image was...

Explanation: In front of a famous background of stars and galaxies lies some of Earth's more unusual trees. Known as quiver trees, they are actually succulent aloe plants that can grow to tree-like proportions. The quiver tree name is derived from the historical usefulness of their hollowed branches as dart holders. Occurring primarily in southern Africa, the trees pictured in the above 16-exposure composite are in Quiver Tree Forest located in southern Namibia. Some of the tallest quiver trees in the park are estimated to be about 300 years old. Behind the trees is light from the small town of...

Explanation: On May 6, the after midnight launch of a SpaceX Falcon 9 rocket lit up dark skies over Merritt Island, planet Earth. Its second stage bound for Earth orbit, the rocket's arc seems to be on course for the center of the Milky Way in this pleasing composite image looking toward the southeast. Two consecutive exposures made with camera fixed to a tripod were combined to follow rocket and home galaxy. A 3 minute long exposure at low sensitivity allowed the rocket's first stage burn to trace the bright orange arc and a 30 second exposure at high sensitivity...

Explanation: Transits of Mercury are relatively rare. Monday's leisurely 7.5 hour long event was only the 2nd of 14 Mercury transits in the 21st century. If you're willing to travel, transits of the International Space Station can be more frequent though, and much quicker. This sharp video frame composite was taken from a well-chosen location in Philadelphia, USA. It follows the space station, moving from upper right to lower left, as it crossed the Sun's disk in 0.6 seconds. Mercury too is included as the small, round, almost stationary silhouette just below center. In apparent size, the International Space Station...

Explanation: On May 9, the diminutive disk of Mercury spent about seven and a half hours crossing in front of the Sun as viewed from the general vicinity of Earth. It was the second of 14 transits of the Solar System's innermost planet in the 21st century. Captured from Fulham, London, England, planet Earth the tiny silhouette shares the enormous solar disk with prominences, filaments, and active regions in this sharp image. But Mercury's round disk (left of center) appears to be the only dark spot, despite the planet-sized sunspots scattered across the Sun. Made with an H-alpha filter that...

Explanation: What's that small black dot moving across the Sun? Mercury. Possibly the clearest view of Mercury crossing in front of the Sun earlier this week was from Earth orbit. The Solar Dynamics Observatory obtained an uninterrupted vista recording it not only in optical light but also in bands of ultraviolet light. Featured here is a composite movie of the crossing set to music. Although the event might prove successful scientifically for better determining components of Mercury' ultra-thin atmosphere, the event surely proved successful culturally by involving people throughout the world in observing a rare astronomical phenomenon. Many spectacular images...

Explanation: Planets, stars, nebulas and a galaxy -- this impressive image has them all. Closest to home are the two planets Mars (right) and Saturn (center), visible as the two bright orange spots in the upper half of the featured image. On the central right are the colorful Rho Ophiuchus star clouds featuring the bright orange star Antares lined up below Mars. These interstellar clouds contain both red emission nebulas and blue reflection nebulas. At the top right of the image is the Blue Horsehead reflection nebula. On the lower left are many dark absorption nebulas that extend from the...

Explanation: Move over Hubble -- here comes the James Webb Space Telescope (JWST). JWST promises to be the new most powerful telescope in space. In the last month, the 18-segment gold-plated primary mirror for JWST was unveiled. In the featured time-lapse video taken last week, the 6.5-meter diameter mirror was raised to a vertical position. The dramatic 30-second sequence shows NASA engineers monitoring the test as room lights glint brightly off the mirror's highly reflective surface. The beryllium mirrors have been coated with a thin film of gold to make them more reflective to infrared light. The science goals of...

Explanation: What's that dot on the Sun? If you look closely, it is almost perfectly round. The dot is the result of an unusual type of solar eclipse that occurred in 2006. Usually it is the Earth's Moon that eclipses the Sun. This time, the planet Mercury took a turn. Like the approach to New Moon before a solar eclipse, the phase of Mercury became a continually thinner crescent as the planet progressed toward an alignment with the Sun. Eventually the phase of Mercury dropped to zero and the dark spot of Mercury crossed our parent star. The situation could...

Explanation: Three new found worlds orbit the ultracool dwarf star TRAPPIST-1, a mere 40 light-years away. Their transits were first detected by the Belgian robotic TRAnsiting Planets and Planetesimals Small Telescope, TRAPPIST, at ESO's La Silla Observatory in Chile. The newly discovered exoplanets are all similar in size to Earth. Because they orbit very close to their faint, tiny star they could also have regions where surface temperatures allow for the presence of liquid water, a key ingredient for life. Their tantalizing proximity to Earth makes them prime candidates for future telescopic explorations of the atmospheres of these potentially habitable...

Explanation: These cosmic clouds have blossomed 1,300 light-years away, in the fertile starfields of the constellation Cepheus. Called the Iris Nebula, NGC 7023 is not the only nebula to evoke the imagery of flowers, though. Still, this deep telescopic image shows off the Iris Nebula's range of colors and symmetries, embedded in surrounding fields of interstellar dust. Within the Iris itself, dusty nebular material surrounds a hot, young star. The dominant color of the brighter reflection nebula is blue, characteristic of dust grains reflecting starlight. Central filaments of the reflection nebula glow with a faint reddish photoluminesence as some dust...

Explanation: Near first quarter, the Moon in March lights this snowy, rugged landscape, a view across the top of Tenerife toward La Palma in the Canary Islands Spanish archipelago. The large Teide volcano, the highest point in Spain, looms over the horizon. Shining above are familiar bright stars of Orion, the Hunter. Adding to the dreamlike scene is the 1 meter diameter prototype telescope of the global network project called the Stellar Observations Network Group or SONG. The SONG's fully robotic observatory was captured during the 30 second exposure while the observatory dome, with slit open, was rotated across the...

Explanation: This coming Monday, Mercury will cross the face of the Sun, as seen from Earth. Called a transit, the last time this happened was in 2006. Because the plane of Mercury's orbit is not exactly coincident with the plane of Earth's orbit, Mercury usually appears to pass over or under the Sun. The above time-lapse sequence, superimposed on a single frame, was taken from a balcony in Belgium shows the entire transit of 2003 May 7. The solar crossing lasted over five hours, so that the above 23 images were taken roughly 15 minutes apart. The north pole of...

Explanation: It was bright and green and stretched across the sky. This striking aurora display was captured last month just outside of Östersund, Sweden. Six photographic fields were merged to create the featured panorama spanning almost 180 degrees. Particularly striking aspects of this aurora include its sweeping arc-like shape and its stark definition. Lake Storsjön is seen in the foreground, while several familiar constellations and the star Polaris are visible through the aurora, far in the background. Coincidently, the aurora appears to avoid the Moon visible on the lower left. The aurora appeared a day after a large hole opened...