The Sagittarius Dwarf Tidal Stream

The Sagittarius Dwarf Tidal Stream



Is our Milky Way Galaxy out to lunch? Recent wide field images and analyses now indicate that our home galaxy is actually still in the process of devouring its closest satellite neighbor. This unfortunate neighbor, the Sagittarius Dwarf galaxy, is now seen to be part of a larger Sagittarius Tidal Stream, a loose filament of stars, gas, and possibly dark matter that entangles the Milky Way. An artist's depiction of the stream is shown above. Speculation also holds that the Sagittarius Dwarf was once pulled through the Milky Way disk very close to our Sun's current location. An important resulting realization is that galaxies contain a jumble of clumps and filaments of both dim and dark matter.

Aurora Over the Chugach Mountains

Aurora Over the Chugach Mountains



Auroras can make spectacular sights. Photographed above, flowing green auroras help the Moon illuminate the serene Portage Lake and the snowy Chugach Mountains near Anchorage, Alaska, USA.Although auroras might first appear to be moonlit clouds, they only add light to the sky and do not block background stars from view. Called northern lights in the northern hemisphere, auroras are caused by collisions between charged particles from the magnetosphere and air moleculeshigh in the Earth's atmosphere.If viewed from space, auroras can be seen to glow in X-ray and ultraviolet light as well. Predictable auroras likely occur a few days after a powerful magnetic event has been seen on the Sun.

Our Galaxy in Stars, Gas, and Dust

Our Galaxy in Stars, Gas, and Dust



The disk of our MilkyWay Galaxy is home to hot nebulae, cold dust, and billions of stars. The red nebulae visible in the above contrast-enhanced picture are primarily emission nebulae, glowing clouds of hydrogengas heated by nearby, bright, young stars. The blue nebulae are primarily reflection nebulae, clouds of gas and fine dust reflecting the light of nearby bright stars. Perhaps the most striking, though, are the areas of darkness, including the Pipe Nebula visible on the image top left. These are lanes of thick dust, many times containing relatively cold molecular clouds of gas. Dust is so plentiful that it obscures the Galactic Center in visible light, hiding its true direction until discovered earlylast century. The diffuse glow comes from billions of older, fainter stars like our Sun,which are typically much older than any of the nebulae. Most of the mass of ourGalaxy remains in a form currentlyunknown.

Surveyor Slides

Surveyor Slides



"Safe!"

IC1340 in the Eastern Veil

IC1340 in the Eastern Veil



These ghostly filaments of interstellar gas are just a smallpart of th expansiveVeil Nebula, seen against a rich fieldof background stars in th long-neckedconstellatio Cygnus.Also known as th Cygnus Loop, the Veil Nebula is supernova remnant,the expanding debris cloud created by a stellarexplosion whose light first reached planet Earthfrom 5,000 to 10,000 years ago.About 1,400 light-years away,the entire nebula now appearsto span over 3 degrees onthe sky, nearly 6 times the apparent size of the full moon,but is faint and can be difficult to see in small telescopes.The region captured i thisbeautiful, deep, color imageis located at the southern tip of the Veil' easterncrescent.It covers about 10 light-years at the distance ofthe Veil and is cataloged as IC1340.

Logarithmic Spirals Isabel and M51

Logarithmic Spirals Isabel and M51



Uncomfortably clos hurricane Isabel (left)and 30 million light-yeardistant galaxy M51 actually don't have much in common.For starters, Isabel was hundreds of miles across, while M51 (th Whirlpool Galaxy)spans about 50,000 light-years making them vastlydissimilar in scale, not to mention the extremely differentphysical interactions which control thei formation an evolution.But they do look amazingly alike, both exhibiting the shape of a simpleand beautiful mathematical curve known as logarithmicspiral, a spiral whose separation grows in geometricway with increasing distance from the center.Also known as th equiangular spiral, growth spiral, and Bernoulli'sspiral or spira mirabilis, this curve' rich properties have fascinate mathematicianssince its discovery by 17th century philosophe Descartes.Intriguingly, this abstract shape is much more abundant in naturethan suggested by the striking visual comparison above.Logarithmic spirals also describe, for example, the arrangement o sunflowerseeds, the shapes of nautilus shells, and .. cauliflower.

M33 Spiral Galaxy in Triangulum

M33 Spiral Galaxy in Triangulum



The small constellatio Triangulumin the northern sky harborsthis magnificent face-on spiral galaxy, M33.Its popular names include the Pinwheel Galaxy or justthe Triangulum Galaxy.M33's diameter spans over 50,000 light-years, making it third largest inthe LocalGroup of galaxies after the Andromeda Galaxy (M31), and ourown Milky Way.About 3 million light-years from the Milky Way, M33lies very close to the Andromeda Galaxy an observersin these two galaxies would likely have spectacular views ofeach other's grand spiral star systems.As for the view from planet Earth, thi sharp27 frame mosaic of M33 nicely shows off blue star clustersand pinkish star forming regions which trace the galaxy'sloosely wound spiral arms.In fact, the cavernous NGC 604 is the brighteststar forming region seen here, visiblealong an arm arcing above and to the rightof the galaxy center.Like M31, M33's population of well-measured variable starshave helped make this nearby spiral cosmicyardstick fo establishingthe distance scale of the Universe.

Egging On the Autumnal Equinox

Egging On the Autumnal Equinox



Today is the autumnal equinox -- should eggs be able to stand on end? This long-standing myth loses much of its mystique after a demonstration that eggs can be made to stand on end during any day of the year. Pictured above, Dr. Phil Plait Sonoma St. U.) acting as the Bad Astronomer balanced three raw eggs on end in late October 1998. Later, more modestly, his wife balanced five more. The little-appreciated fact that most eggshells have small bumps on them makes this seemingly impossible task achievable. Although, during an equinox, every place on Earth experiences an equal length day and night (12 hours each), this fact has no practical effect on egg stability.

Opportunity Rockets Toward Mars

Opportunity Rockets Toward Mars



Next stop: Mars. Two months ago, the second of two missions to Mars was launched from Cape Canaveral, Florida, USA above a Boeing Delta II rocket.The Mars Exploration Rover dubbed Opportunity is expected to arrive at the red planet this coming January. Pictured above, an attached RocketCam (TM) captures Opportunityseparating from lower booster stages and rocketing off towardMars.Upon arriving, parachutes will deploy to slow the spacecraft and surrounding airbags will inflate. The balloon-like package will then bounce around the surface a dozen times or more before coming to a stop. The airbags will then deflate, the spacecraft will right itself, and the Opportunity rover will prepare to roll onto Mars. A first rover named Spirit was successfully launched on June 10 and will arrive at Mars a few weeks earlier. The robots Spirit and Opportunity are expected to cover as much as 40 metres per day, much more than Sojourner, their 1997 predecessor. Spirit and Opportunity will search for evidence of ancient Martian water, from which implications might be drawn about the possibility of ancient Martian life.

Inside the Eagle Nebula

Inside the Eagle Nebula



From afar, the whole thing looks like an Eagle. A closer look at the Eagle Nebula, however, shows the bright region is actually a window into the center of a larger dark shell of dust. Through this window, a brightly-lit workshop appears where a whole open cluster of stars is being formed. In this cavity tall pillars and round globules of dark dust and cold molecular gasremain where stars are still forming. Already visible are several young bright blue stars whose light and winds are burning away and pushing back the remaining filaments and walls of gas and dust. The Eagle emission nebula, tagged M16, lies about 6500 light years away, spans about 20 light-years, and is visible with binoculars toward the constellation of Serpens. The above picture combines three specific emitted colors and was taken with the 0.9-meter telescope on Kitt Peak, Arizona, USA.