Sharp telescopic views of magnificent edge-on spiral galaxy NGC 3628 show a puffy galactic disk divided by dark dust lanes. Of course, this deep galactic portrait puts some astronomers in mind of its popular moniker, The Hamburger Galaxy. The tantalizing island universe is about 100,000 light-years across and 35 million light-years away in the northern springtime constellation Leo. NGC 3628 shares its neighborhood in the local Universe with two other large spirals M65 and M66 in a grouping otherwise known as the Leo Triplet. Gravitational interactions with its cosmic neighbors are likely responsible for the extended flare and warp of this spiral's disk.

How many different astronomical phenomena have come together to create the above vista? Several. First, in the foreground, is Crater Lake -- a caldera created by volcanism on planet Earth about 7,700 years ago. Next, inside the lake, is water. Although the origin of the water in the crater is melted snowfall, the origin of water on Earth more generally is unclear, but possibly related to ancient Earthly-impacts of icy bodies. Next, the green glow in the sky is airglow, light emitted by atoms high in the Earth's atmosphere as they recombine at night after being separated during the day by energetic sunlight. The many points of light in the sky are stars, glowing by nuclear fusion. They are far above the atmosphere but nearby to our Sun in the Milky Way Galaxy. Finally, the bright arch across the image is the central band of the Milky Way, much further away, on the average, than the nearby stars, and shaped mostly by gravity. Contrary to appearances, the Milky Way band glows by itself and is not illuminated by the airglow. The above image is a six-frame panorama taken during about two weeks ago in Oregon, USA.

What creates these long and nearly straight grooves on Mars? Dubbed linear gullies, they appear on the sides of some sandy slopes during Martian spring, have nearly constant width, extend for as long as two kilometers, and have raised banks along their sides. Unlike most water flows, they do not appear to have areas of dried debris at the downhill end. A leading hypothesis -- actually being tested here on Earth -- is that these linear gullies are caused by chunks of carbon dioxide ice (dry ice) breaking off and sliding down hills while sublimating into gas, eventually completely evaporating into thin air. If true, these natural dry-ice sleds may well provide future adventurers a smooth ride on cushions of escaping carbon dioxide. The above recently-released image was taken in 2006 by the HiRISE camera on board the NASA's Mars Reconnaissance Orbiter currently orbiting Mars. Astrophysicists: Browse 600+ codes in the Astrophysics Source Code Library

The first APOD appeared eighteen years ago today, on 1995 June 16. Although garnering only 14 pageviews on that day, we are proud to estimate that APOD has now served over one billion space-related images over the past eighteen years. That early beginning, along with a nearly unchanging format, has allowed APOD to be a consistent and familiar site on a web frequently filled with change. Many people don't know, though, that APOD is now translated daily into many major languages. We again thank our readers, astrophotographers, and NASA for their continued support, but ask that any potentially congratulatory e-mail go this year to the volunteers all around the world who translate APOD's captions daily, many times with considerable effort. Some APOD images are featured in the above spectacular collage visualizing APOD as a classic film reel, submitted by an APOD enthusiast skilled in digital image manipulation. How many APOD images can you identify? APOD is also available in: Arabic, Bahasa Indonesian, Catalan, Chinese, Chinese, Czech, Dutch, Farsi, Farsi, Galego, German, French, Hebrew, Japanese, Polish, Portuguese, Romanian, Russian, Slovenian, Spanish, Thai, or Turkish

Over a five hour period last Tuesday morning, exposures captured this tantalizing view of meteor streaks and the Milky Way in dark skies above Las Campanas Observatory in Chile. During that time, astronomers had hoped to see an outburst from the gamma Delphinid meteor shower as Earth swept through the dust trail left by an unknown comet. Named for the shower's radiant point in the constellation Delphinus, a brief but strong outburst was reported in bright, moonlit skies on June 10, 1930. While no strong Delphinid meteor activity was reported since, an outburst was tentatively predicted to occur again in 2013. But even though Tuesday's skies were dark, the overall rate of meteors in this field is low, and only the three lower meteor streaks seem to point back to the shower's estimated radiant.

Sharpless 115 stands just north and west of Deneb, the alpha star of Cygnus the Swan in planet Earth's skies. Noted in the 1959 catalog by astronomer Stewart Sharpless (as Sh2-115) the faint but lovely emission nebula lies along the edge of one of the outer Milky Way's giant molecular clouds, about 7,500 light-years away. Shining with the light of ionized atoms of hydrogen, sulfur, and oxygen in this Hubble palette color composite image, the nebular glow is powered by hot stars in star cluster Berkeley 90. The cluster stars are likely only 100 million years old or so and are still embedded in Sharpless 115. But the stars' strong winds and radiation have cleared away much of their dusty, natal cloud. At the emission nebula's estimated distance, this cosmic close-up spans just under 100 light-years.

You can see four planets in this serene sunset image, created from a series of stacked digital exposures captured near dusk on May 25. The composite picture follows the trail of three of them, Jupiter, Venus, and Mercury (left to right) dropping toward the western horizon, gathered close in last month's remarkable triple planetary conjunction. Similar in brightness to planet Mercury, the star Elnath (Beta Tauri) is also tracked across the scene, leaving its dotted trail still farther to the right. Of course, in the foreground are the still, shallow waters of Alikes salt lake, reflecting the striking colors of sunset over Kos Island, Greece, planet Earth. For now, Jupiter has wandered into the glare of the setting Sun, but Mercury and Venus remain low in the west at twilight.

What's happening in the NGC 3582 nebula? Bright stars and interesting molecules are forming. The complex nebula resides in the star forming region called RCW 57. Visible in this image are dense knots of dark interstellar dust, bright stars that have formed in the past few million years, fields of glowing hydrogen gas ionized by these stars, and great loops of gas expelled by dying stars. A detailed study of NGC 3582, also known as NGC 3584 and NGC 3576, uncovered at least 33 massive stars in the end stages of formation, and the clear presence of the complex carbon molecules known as polycyclic aromatic hydrocarbons (PAHs). PAHs are thought to be created in the cooling gas of star forming regions, and their development in the Sun's formation nebula five billion years ago may have been an important step in the development of life on Earth. The above image was taken at the Desert Hollow Observatory north of Phoenix, Arizona, USA. Follow APOD on: Facebook (Daily) (Sky) (Spanish) or Google Plus (Daily) (River)

Where are the hottest stars in the nearest galaxies? To help find out, NASA commissioned its Earth-orbiting Swift satellite to compile a multi-image mosaic of the neighboring Large Magellanic Cloud (LMC) galaxy in ultraviolet light. The above image shows where recently formed stars occur in the LMC, as the most massive of these young stars shine brightly in blue and ultraviolet. In contrast, visible in an image roll-over, a more familiar view of the LMC in visible light better highlights older stars. On the upper left is one of the largest star forming regions known in the entire Local Group of galaxies: the Tarantula Nebula. The Large Magellanic Cloud and its smaller companion the Small Magellanic Cloud are easily visible with the unaided eye to sky enthusiasts with a view of the southern sky. Detailed inspection of the above image is allowing a better galaxy-comprehensive picture for how star formation occurs.

Many bright nebulae and star clusters in planet Earth's sky are associated with the name of astronomer Charles Messier, from his famous 18th century catalog. His name is also given to these two large and remarkable craters on the Moon. Standouts in the dark, smooth lunar Sea of Fertility or Mare Fecunditatis, Messier (left) and Messier A have dimensions of 15 by 8 and 16 by 11 kilometers respectively. Their elongated shapes are explained by an extremely shallow-angle trajectory followed by the impactor, moving left to right, that gouged out the craters. The shallow impact also resulted in two bright rays of material extending along the surface to the right, beyond the picture. Intended to be viewed with red/blue glasses (red for the left eye), this striking stereo picture of the crater pair was recently created from high resolution scans of two images (AS11-42-6304, AS11-42-6305) taken during the Apollo 11 mission to the moon. Surf the Universe: Click here to see a randomly selected APOD!

The bright clusters and nebulae of planet Earth's night sky are often named for flowers or insects. Though its wingspan covers over 3 light-years, NGC 6302 is no exception. With an estimated surface temperature of about 250,000 degrees C, the dying central star of this particular planetary nebula has become exceptionally hot, shining brightly in ultraviolet light but hidden from direct view by a dense torus of dust. This sharp and colorful close-up of the dying star's nebula was recorded in 2009 by the Hubble Space Telescope's Wide Field Camera 3, installed during the final shuttle servicing mission. Cutting across a bright cavity of ionized gas, the dust torus surrounding the central star is near the center of this view, almost edge-on to the line-of-sight. Molecular hydrogen has been detected in the hot star's dusty cosmic shroud. NGC 6302 lies about 4,000 light-years away in the arachnologically correct constellation of the Scorpion (Scorpius).

Except for the rings of Saturn, the Ring Nebula (M57) is probably the most famous celestial band. Its classic appearance is understood to be due to our own perspective, though. The recent mapping of the expanding nebula's 3-D structure, based in part on this clear Hubble image, indicates that the nebula is a relatively dense, donut-like ring wrapped around the middle of a football-shaped cloud of glowing gas. The view from planet Earth looks down the long axis of the football, face-on to the ring. Of course, in this well-studied example of a planetary nebula, the glowing material does not come from planets. Instead, the gaseous shroud represents outer layers expelled from the dying, once sun-like star, now a tiny pinprick of light seen at the nebula's center. Intense ultraviolet light from the hot central star ionizes atoms in the gas. In the picture, the blue color in the center is ionized helium, the cyan color of the inner ring is the glow of hydrogen and oxygen, and the reddish color of the outer ring is from nitrogen and sulfur. The Ring Nebula is about one light-year across and 2,000 light-years away.