Higher than the highest mountain lies the realm of the aurora. Auroras rarely reach below 60 kilometers, and can range up to 1000 kilometers. Aurora light results from energetic electrons and protons striking atoms and molecules in the Earth's atmosphere. Somewhat uncommon, an auroral corona appears as a center point for a surrounding display and may occur when an aurora develops directly overhead, or when auroral rays are pointed nearly toward the observer. This picturesque but brief green and purple aurora exhibition occurred last month high above Kvaløya, Tromsø, Norway. The Sessøyfjorden fjord runs through the foreground, while numerous stars are visible far in the distance. APOD Wall Calendar: Land and Skyscapes

How did a star create the Helix nebula? The shapes of planetary nebula like the Helix are important because they likely hold clues to how stars like the Sun end their lives. Observations by the orbiting Hubble Space Telescope and the 4-meter Blanco Telescope in Chile, however, have shown the Helix is not really a simple helix. Rather, it incorporates two nearly perpendicular disks as well as arcs, shocks, and even features not well understood. Even so, many strikingly geometric symmetries remain. How a single Sun-like star created such beautiful yet geometric complexity is a topic of research. The Helix Nebula is the nearest planetary nebula to Earth, lies only about 700 light years away toward the constellation of Aquarius, and spans about 3 light-years. APOD Wall Calendar: Nebulas and Star Clusters

How did a star create the Helix nebula? The shapes of planetary nebula like the Helix are important because they likely hold clues to how stars like the Sun end their lives. Observations by the orbiting Hubble Space Telescope and the 4-meter Blanco Telescope in Chile, however, have shown the Helix is not really a simple helix. Rather, it incorporates two nearly perpendicular disks as well as arcs, shocks, and even features not well understood. Even so, many strikingly geometric symmetries remain. How a single Sun-like star created such beautiful yet geometric complexity is a topic of research. The Helix Nebula is the nearest planetary nebula to Earth, lies only about 700 light years away toward the constellation of Aquarius, and spans about 3 light-years. APOD Wall Calendar: Nebulas and Star Clusters

As the Moon rose and the Sun set on October 8, a lunar eclipse was in progress seen from Chongqing, China. Trailing through this composite time exposure, the rising Moon began as a dark reddened disk in total eclipse near the eastern horizon. Steadily climbing above the populous city's colorful lights along the Yangtze River, the moontrail grows brighter and broader, until a bright Full Moon emerged from the Earth's shadow in evening skies. Although lunar eclipses are not always total ones, this eclipse, along with last April's lunar eclipse, were the first two of four consecutive total lunar eclipses, a series known as a tetrad. The final two eclipses of this tetrad will occur in early April and late September 2015.

From the early hours of October 8, over the Santa Cruz Mountains near Los Gatos, California, the totally eclipsed Moon shows a range of color across this well-exposed telescopic view of the lunar eclipse. Of course, a lunar eclipse can only occur when the Moon is opposite the Sun in Earth's sky and gliding through the planet's shadow. But also near opposition during this eclipse, and remarkably only half a degree or so from the lunar limb, distant Uranus is faint but easy to spot at the lower right. Fainter still are the ice giant's moons. To find them, slide your cursor over the image (or just follow this link) to check out a longer exposure. While even the darkened surface of our eclipsed Moon will be strongly overexposed, Uranus moons Titania, Oberon, and Umbriel can just be distinguished as faint pinpricks of light.

The Pacific Ocean and Chilean coast lie below this sea of clouds. Seen through the subtle colors of the predawn sky a lunar eclipse is in progress above, the partially eclipsed Moon growing dark. The curved edge of planet Earth's shadow still cuts across the middle of the lunar disk as the Moon sinks lower toward the western horizon. In fact, from this southern hemisphere location as well as much of eastern North America totality, the Moon completely immersed within Earth's shadow, began near the time of moonset and sunrise on October 8. From farther west the total phase could be followed for almost an hour though, the darker reddened Moon still high in the night sky.

Star cluster NGC 6823 is slowly turning gas clouds into stars. The center of the open cluster, visible on the upper right, formed only about two million years ago and is dominated in brightness by a host of bright young blue stars. Some outer parts of the cluster, visible in the featured image's center as the stars and pillars of emission nebula NGC 6820, contain even younger stars. The huge pillars of gas and dust likely get their elongated shape by erosion from hot radiation emitted from the brightest cluster stars. Striking dark globules of gas and dust are also visible across the upper left of the featured image. Open star cluster NGC 6823 spans about 50 light years and lies about 6000 light years away toward the constellation of the Fox (Vulpecula). APOD Wall Calendar: Nebulas and Star Clusters

What connects the Sun to the Moon? Many answers have been given throughout history, but in the case of today's featured image, it appears to be the plane of our Milky Way Galaxy. The 16-image panorama was taken in Capitol Reef National Park, Utah, USA where two sandstone monoliths -- the Temple of the Moon on the right and the Temple of the Sun on the left -- rise dramatically from the desert. Each natural monument stands about 100 meters tall and survives from the Jurassic period 160 million years ago. Even older are many of the stars and nebulas that dot the celestial background, including the Andromeda Galaxy. Tomorrow the Earth will connect the Sun to the Moon by way of its shadow: a total lunar eclipse will be visible from many locations around the globe. New: Follow APOD on Ello

Where did all these high energy positrons come from? The Alpha Magnetic Spectrometer (AMS-02) onboard the International Space Station (ISS) has been meticulously recording how often it is struck by both high energy electrons and positrons since 2011. After accumulating years of data, it has now become clear that there are significantly more positrons than expected at the highest energies detected. The excess may have a very exciting and profound origin -- the annihilation of distant but previously undetected dark matter particles. However, it is also possible that astronomical sources such as pulsars are creating the unexplained discrepancy. The topic remains a very active area of research. Pictured here, the AMS is visible on the ISS just after being installed, with a US Space Shuttle docked on the far right, a Russian Soyuz capsule docked on the far left, and the blue Earth that houses all nations visible across the background. Follow APOD on: Facebook, Google Plus, or Twitter

Mars, Antares, Moon, and Saturn are the brightest celestial beacons in this serene sky. The Sun's golden light is still scattered along the southwestern horizon though, captured after sunset on September 28. The evening gathering of wandering planets and Moon along with the bright star viewed as an equal to Mars and the Scorpion's Heart was enjoyed around planet Earth. But from the photographer's perspective looking across the calm waters of Lake Balaton, Hungary, they were joined by a more terrestrial sailboat mast light. Mast light, bright star, planets and Moon are all posing near the plane of the ecliptic.

Stepping stones seem to lead to the Milky Way as it stretches across this little sky. Of course, the scene is really the northern hemisphere's autumnal equinox night. Water and sky are inverted by a top to bottom, around the horizon stereographic projection centered on the zenith above Lake Storsjön in Jämtland, Sweden. In the north the Milky Way arcs from east to west overhead as fall begins, but the season is also a good time for viewing aurora. Geomagnetic storms increase in frequency near the equinox and produce remarkable displays of northern lights at high latitudes, like the eerie greenish glow reflected in this watery cosmos.

Blown by the wind from a massive star, this interstellar apparition has a surprisingly familiar shape. Cataloged as NGC 7635, it is also known simply as The Bubble Nebula. Although it looks delicate, the 10 light-year diameter bubble offers evidence of violent processes at work. Below and left of the Bubble's center is a hot, O star, several hundred thousand times more luminous and around 45 times more massive than the Sun. A fierce stellar wind and intense radiation from that star has blasted out the structure of glowing gas against denser material in a surrounding molecular cloud. The intriguing Bubble Nebula and associated cloud complex lie a mere 11,000 light-years away toward the boastful constellation Cassiopeia. This tantalizing view of the cosmic bubble is composed from narrowband image data, recording emission from the region's ionized hydrogen and oxygen atoms. To create the three color image, hydrogen and oxygen emission were used for red and blue and combined to create the green channel.