M27: Not A Comet

Explanation:
While searching the skies above 18th century France for comets, astronomer Charles Messier diligently recorded this object as number 27 on his list of things which are definitely not comets. So what is it? Well, 20th century astronomers would classify it as a Planetary Nebula ... but it's not a planet either, even though it may appear round and planet-like in a small telescope. Messier 27 (M27) is now known to be an excellent example of a gaseous emission nebula created as a sun-like star runs out of nuclear fuel in its core. The nebula forms as the star's outer layers are expelled into space, with a visible glow generated by atoms excited by the dying star's intense but invisible ultraviolet light. Known by the popular name of the Dumbbell Nebula, the beautifully symmetric interstellar gas cloud is about 1,200 light-years away in the constellation Vulpecula. This intriguing color composite view was recorded through narrow band filters sensitive to emission from hydrogen atoms (shown in red) and oxygen atoms (shown in blue/green).

Burns Cliff Anaglyph

Explanation:
Get out your red/blue glasses and gaze across Burns Cliff along the inner wall of Endurance crater on Mars! The view from the perspective of Mars rover Opportunity is a color anaglyph - two different images are presented to the left and right eyes by color filters to produce the 3D effect. Scroll the picture to the right to see the full 180 degree panorama. Still returning science data and images, both Spirit and Opportunity rovers completed 2 years of Mars exploration in January. Opportunity spent the month of July on the road to Victoria crater. The stereo pair of images used to create this view are based on image data recorded in November 2004.

Still Life with NGC 2170

Explanation:
In this beautiful celestial still life composed with a cosmic brush, dusty nebula NGC 2170 shines at the upper left. Reflecting the light of nearby hot stars, NGC 2170 is joined by other bluish reflection nebulae and a compact red emission region against a backdrop of stars. Like the common household items still life painters often choose for their subjects, the clouds of gas, dust, and hot stars pictured here are also commonly found in this setting - a massive, star-forming molecular cloud in the constellation Monoceros. The giant molecular cloud, Mon R2, is impressively close, estimated to be only 2,400 light-years or so away. At that distance, this canvas would be about 15 light-years across

A Cerro Tololo Sky

Explanation:
High atop a Chilean mountain lies one of the premier observatories of the southern sky: the Cerro Tololo Inter-American Observatory (CTIO). Pictured above is the dome surrounding one of the site's best known instruments, the 4-meter Blanco Telescope. Far behind the dome are thousands of individual stars and diffuse light from three galaxies: the Small Magellanic Cloud (upper left), the Large Magellanic Cloud (lower left), and our Milky Way Galaxy (right). Also visible just to Blanco's right is the famous superposition of four bright stars known as the Southern Cross. A single 20 second exposure, this digital image was recorded with a sensitive detector intended for astronomical imaging.

An Erupting Solar Prominence from SOHO

Explanation:
Our Sun is still very active. In the year 2000, our Sun went though Solar Maximum, the time in its 11-year cycle where the most sunspots and explosive activities occur. Sunspots, the Solar Cycle, and solar prominences are all caused by the Sun's changing magnetic field. Pictured above is a solar prominence that erupted in 2002 July, throwing electrons and ions out into the Solar System. The above image was taken in the ultraviolet light emitted by a specific type of ionized helium, a common element on the Sun. Particularly hot areas appear in white, while relatively cool areas appear in red. Our Sun should gradually quiet down until Solar Minimum occurs, and the Sun is most quiet. No one can precisely predict when Solar Minimum will occur, although some signs indicate that it has started already!

Horse Head Shaped Reflection Nebula IC 4592

Explanation:
Do you see the horse's head? What you are seeing is not the famous Horsehead nebula toward Orion but rather a fainter nebula that only takes on a familiar form with deeper imaging. The main part of the above imaged molecular cloud complex is a reflection nebula cataloged as IC 4592. Reflection nebulas are actually made up of very fine dust that normally appears dark but can look quite blue when reflecting the light of energetic nearby stars. In this case, the source of much of the reflected light is a star at the eye of the horse. That star is part of Nu Scorpii, one of the brighter star systems toward the constellation of Scorpius. A second reflection nebula dubbed IC 4601 is visible surrounding two stars on the far right.

Magellanic Morning

Explanation:
This early morning skyscape recorded near Winton, Queensland, Australia, looks toward the southeast. Low clouds are seen in silhouette against the first hints of sunlight, while two famous cosmic clouds, the Clouds of Magellan, also hover in the brightening sky. The Small Magellanic Cloud (SMC, upper right), and the Large Magellanic Cloud (LMC) are prominent wonders of the southern sky, named for the 16th century Portuguese explorer Ferdinand Magellan. They are small, irregular galaxies in their own right, satellites of our much larger, spiral Milky Way galaxy. The SMC is about 210,000 light-years and the LMC about 180,000 light-years away. At lower left, bright star Canopus (Alpha Carinae), denizen of the Milky Way, is a mere 310 light-years distant.

Galactic Center Star Clusters

Explanation:
If you had x-ray vision, the central regions of our Galaxy would not be hidden from view by cosmic dust clouds. Instead, the Milky Way toward Sagittarius might look something like this. Pleasing to look at, the gorgeous false-color representation of x-ray data from the Chandra Observatory shows high energies in blue, medium in green, and low energy x-rays in red. The mosaic spans about 130 light-years at the 26,000 light-year distance of the Galactic Center. It reveals massive, x-ray emitting star clusters in a crowded environment. In particular, the Galactic Center cluster and the enormous black hole Sagittarius A* are within the bright region near the bottom. Two other star clusters, the Arches, and the Quintuplet lie near the top. Cluster interactions with dense molecular clouds in the region may produce some of the diffuse emission detected in the Chandra x-ray view.

Perseid in the Light

Explanation:
Dark skies are favored for viewing meteor showers -- so many are pessimistic about this year's Perseids. While the Perseid meteor shower is scheduled to peak this weekend, bright light from an almost full Moon will also flood the night and mask the majority of relatively faint meteors. Still, skygazing in the evening before the Moon rises (before about 10 PM local time) could reveal spectacular earthgrazing meteors. Persisting even later into the moonlit night can reward northern hemisphere watchers looking for occasional Perseid fireballs. In fact, astronomer Jimmy Westlake imaged this bright Perseid meteor despite the combination of moonlight and auroral glow over Colorado skies in August of 2000.

The First Explorer

Explanation:
Inaugurating the era of space exploration for the US, the First Explorer, a thirty pound satellite, was launched into Earth orbit on January 31, 1958 by the Army Ballistic Missile Agency. Explorer I carried instruments to measure temperatures, micrometeorite impacts, and an experiment designed by James A. Van Allen to measure the density of electrons and ions in space. The measurements made by Van Allen's experiment led to an unexpected and startling discovery -- an earth-encircling belt of high energy electrons and ions trapped in the magnetosphere now known as the Van Allen Radiation Belt. Explorer I ceased transmitting on February 28 of that year but remained in orbit until March of 1970. Pioneering astrophysicist James Van Allen died on August 9th at the age of 91.