NASA's A.P.O.D.

A Picturesque Venus Transit
Image Credit & Copyright: David Cortner

Explanation: The rare transit of Venus across the face of the Sun in 2004 was one of the better-photographed events in sky history. Both scientific and artistic images flooded in from the areas that could see the transit: Europe and much of Asia, Africa, and North America. Scientifically, solar photographers confirmed that the black drop effect is really better related to the viewing clarity of the camera or telescope than the atmosphere of Venus. Artistically, images might be divided into several categories. One type captures the transit in front of a highly detailed Sun. Another category captures a double coincidence such as both Venus and an airplane simultaneously silhouetted, or Venus and the International Space Station in low Earth orbit. A third image type involves a fortuitous arrangement of interesting looking clouds, as shown by example in the above image taken from North Carolina, USA. Sky enthusiasts worldwide are abuzz about the coming transit of Venus on Tuesday. It is perhaps interesting to wonder whether any person will live to see — and remember seeing — both Tuesday’s Venus transit and the next one in 2117.

M51: The Whirlpool Galaxy
Image Credit & Copyright: Marco Burali, Tiziano Capecchi, Marco Mancini (Osservatorio MTM)

Explanation: Follow the handle of the Big Dipper away from the dipper’s bowl until you get to the handle’s last bright star. Then, just slide your telescope a little south and west and you might find this stunning pair of interacting galaxies, the 51st entry in Charles Messier famous catalog. Perhaps the original spiral nebula, the large galaxy with well defined spiral structure is also cataloged as NGC 5194. Its spiral arms and dust lanes clearly sweep in front of its companion galaxy (top), NGC 5195. The pair are about 31 million light-years distant and officially lie within the angular boundaries of the small constellation Canes Venatici. Though M51 looks faint and fuzzy to the human eye, deep images like this one can reveal the faint tidal debris around the smaller galaxy.

A Sagittarius Triplet
Image Credit & Copyright: Martin Pugh

Explanation: These three bright nebulae are often featured in telescopic tours of the constellation Sagittarius and the crowded starfields of the central Milky Way. In fact, 18th century cosmic tourist Charles Messier cataloged two of them; M8, the large nebula left of center, and colorful M20 on the right. The third, NGC 6559, is above M8, separated from the larger nebula by a dark dust lane. All three are stellar nurseries about five thousand light-years or so distant. The expansive M8, over a hundred light-years across, is also known as the Lagoon Nebula. M20’s popular moniker is the Trifid. Glowing hydrogen gas creates the dominant red color of the emission nebulae, with contrasting blue hues, most striking in the Trifid, due to dust reflected starlight. This broad skyscape also includes one of Messier’s open star clusters, M21, just above and right of the Trifid.

Lantern Saturn
Credit: VIMS Team, U. Arizona, ESA, NASA

Explanation: Known for its bright ring system and many moons, gas giant Saturn looks strange and unfamiliar in this false-color view from the Cassini spacecraft. In fact, in this Visual and Infrared Mapping Spectrometer (VIMS) mosaic the famous rings are almost invisible, seen edge-on cutting across picture center. The most striking contrast in the image is along the terminator or boundary between night and day. To the right (day side) blue-green hues are visible sunlight reflected from Saturn’s cloud tops. But on the left (night side) in the absence of sunlight, the lantern-like glow of infrared radiation from the planet’s warm interior silhouettes features at Saturn’s deeper cloud levels. The infrared glow also shines from the broad shadows of Saturn’s rings sweeping across the planet’s upper hemisphere.

Looking Back at an Eclipsed Earth
Image Credit: PHL @ UPR Arecibo, NASA, EUMETSAT, NERC Satellite Receiving Station, U. Dundee

Explanation: What’s that dark spot on planet Earth? It’s the shadow of the Moon. The above image of Earth was taken last week by MTSAT during an annular eclipse of the Sun. The dark spot appears quite unusual as clouds are white and the oceans are blue in this color corrected image. Earthlings residing within the dark spot would see part of the Sun blocked by the Moon and so receive less sunlight than normal. The spot moved across the Earth at nearly 2,000 kilometers per hour, giving many viewers less than two hours to see a partially eclipsed Sun. MTSAT circles the Earth in a geostationary orbit and so took the above image from about three Earth-diameters away. Sky enthusiasts might want to keep their eyes pointed upward this coming week as a partial eclipse of the Moon will occur on June 4 and a transit of Venus across the face of the Sun will occur on June 5.

Contemplating the Sun
Image Credit & Copyright: Steven Gilbert

Explanation: Have you contemplated your home star recently? Pictured above, a Sun partially eclipsed on the top left by the Moon is also seen eclipsed by earthlings contemplating the eclipse below. The above menagerie of silhouettes was taken from the Glen Canyon National Recreation Area near Page, Arizona, USA, where park rangers and astronomers expounded on the unusual event to interested gatherers. Also faintly visible on the Sun’s disk, just to the lower right of the dark Moon’s disk, is a group of sunspots. Although exciting, some consider this event a warm-up act for next week’s chance to comtemplate the Sun — a much more rare partial eclipse by the planet Venus.

At the Edge of NGC 891 
Credit: Composite Image Data - Subaru Telescope (NAOJ), Hubble Legacy Archive,
Michael Joner, David Laney (West Mountain Observatory, BYU); Processing - Robert Gendler

Explanation: This sharp cosmic portrait features NGC 891. The spiral galaxy spans about 100 thousand light-years and is seen almost exactly edge-on from our perspective. In fact, about 30 million light-years distant in the constellation Andromeda, NGC 891 looks a lot like our Milky Way. At first glance, it has a flat, thin, galactic disk and a central bulge cut along the middle by regions of dark obscuring dust. The combined image data also reveals the galaxy’s young blue star clusters and telltale pinkish star forming regions. And remarkably apparent in NGC 891’s edge-on presentation are filaments of dust that extend hundreds of light-years above and below the center line. The dust has likely been blown out of the disk by supernova explosions or intense star formation activity. Faint neighboring galaxies can also been seen near this galaxy’s disk.

Scorpius in Red and Blue
Image Credit & Copyright: John Davis

Explanation: Cosmic dust clouds dim the light of background stars. But they also reflect the light of stars nearby. Since bright stars tend to radiate strongly in the blue portion of the visible spectrum, and the interstellar dust scatters blue light more strongly than red, the dusty reflection nebulae tend to be blue. Lovely examples are the wispy blue reflection nebulae near bright, hot stars Pi and Delta Scorpii (upper left and lower right) in this telescopic skyscape from the head of the constellation Scorpius. Of course, the contrasting red emission nebulae are also caused by the hot stars’ energetic radiation. Ultraviolet photons ionize hydrogen atoms in the interstellar clouds producing the characteristic red hydrogen alpha emission line as the electrons recombine. About 600 light-years away, the nebulae are found in the second version of the Sharpless Catalog as Sh2-1 (left, with reflection nebulae VdB 99) and Sh2-7. At that distance, this field of view is about 40 light-years across.

All the Water on Europa
Illustration Credit & Copyright: Kevin Hand (JPL/Caltech),
Jack Cook (Woods Hole Oceanographic Institution), Howard Perlman (USGS)

Explanation: How much of Jupiter’s moon Europa is made of water? A lot, actually. Based on the Galileo probe data acquired during its exploration of the Jovian system from 1995 to 2003, Europa possesses a deep, global ocean of liquid water beneath a layer of surface ice. The subsurface ocean plus ice layer could range from 80 to 170 kilometers in average depth. Adopting an estimate of 100 kilometers depth, if all the water on Europa were gathered into a ball it would have a radius of 877 kilometers. To scale, this intriguing illustration compares that hypothetical ball of all the water on Europa to the size of Europa itself (left) - and similarly to all the water on planet Earth. With a volume 2-3 times the volume of water in Earth’s oceans, the global ocean on Europa holds out a tantalizing destination in the search for extraterrestrial life in our solar system.

SpaceX’s Falcon 9 Launches to the Space Station
Image Credit: NASA

Explanation: This fire-breathing Dragon can fly. Pictured above yesterday, SpaceX Corporation’s Falcon 9 rocket capped with a Dragon spacecraft lifted off from Cape Canaveral, Florida, USA. The successful launch was significant not only because it demonstrated that a private company has the ability to re-supply the International Space Station (ISS), but also that spaceflight has taken a significant step away from being an endeavor that only big governments can do with public money. If all continues as planned, the robotic Dragon will dock with the ISS this weekend. Over the next two weeks, the ISS Expedition 31 crew will then unload Dragon and refill it with used scientific equipment. In about three weeks, the ISS’s robotic arm will then undock Dragon and move it to where it can fire its rockets. Soon thereafter the Dragon capsule is expected to reenter the Earth’s atmosphere, deploy its parachutes, splash down in the Pacific Ocean off the coast of California, and be recovered.