Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2022 April 17

Shuttle Over Earth

Image Credit: NASA, Expedition 22 Crew

Explanation: What’s that approaching? Astronauts on board the International Space Station in 2010 first saw it far in the distance. Soon it enlarged to become a dark silhouette. As it came even closer, the silhouette appeared to be a spaceship. Finally, the object revealed itself to be the Space Shuttle Endeavour, and it soon docked as expected with the Earth-orbiting space station. Pictured here, Endeavour was imaged near Earth’s horizon as it approached, where several layers of the Earth’s atmosphere were visible. Directly behind the shuttle is the mesosphere, which appears blue. The atmospheric layer that appears white is the stratosphere, while the orange layer is Earth’s Troposphere. Together, these thin layers of air — collectively spanning less than 2 percent of Earth‘s radius — sustain us all in many ways, including providing oxygen to breath and a barrier to dangerous radiations from space.

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2022 April 16

Orion Pines

Image Credit & Copyright: Juan Carlos Casado (Starry Earth, TWAN)

Explanation: Taken with a camera fixed to a tripod, many short exposures were aligned with the stars to unveil this beautiful, dark night sky. Captured near the rural village of Albany`a at the northeastern corner of Spain, the three stars of Orion’s belt stretch across top center in the starry frame. Alnitak, the easternmost (left) of the belt stars is seen next to the more diffuse glow of the Flame Nebula and the dark notch of the famous Horsehead. Easily visible to the naked-eye The Great Nebula of Orion is below the belt stars. A mere 1,500 light-years distant, it is the closest large stellar nursery to our fair planet. Best seen in photographs, the broad and faint arc of Barnard’s Loop seems to embrace Orion’s brighter stars and nebulae though. In the northern spring the familiar northern winter constellation is setting. Near the western horizon toward lower right Orion’s apparently bright blue supergiant Rigel just touches the branches of a pine tree.

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2022 April 15

The Gator-back Rocks of Mars

Image Credit: NASA, JPL-Caltech, MSSS

Explanation: Wind-sharpened rocks known as ventifacts, cover this broad sloping plain in the foot hills of Mount Sharp, Gale crater, Mars. Dubbed gator-back rocks their rugged, scaly appearance is captured in these digitally stitched Mastcam frames from the Curiosity rover on mission sol 3,415 (March 15, 2022). Driving over gator-back rocks before has resulted in damage to the rover’s wheels, so Curiosity team members decided to turn around and take another path to continue the rover’s climb. Curiosity has been on an ascent of Gale crater’s central 5.5 kilometer high mountain since 2014. As it climbs, it’s been able to study layers shaped by water on Mars billions of years ago.

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2022 April 13

Milky Way over Devils Tower

Image Credit & Copyright: MaryBeth Kiczenski

Explanation: What created Devils Tower? The origin of this extraordinary rock monolith in Wyoming, USA is still debated, with a leading hypothesis holding that it is a hardened lava plume that never reached the surface to become a volcano. In this theory, the lighter rock that once surrounded the dense volcanic neck has now eroded away, leaving the dramatic tower. Known by Native Americans by names including Bear’s Lodge and Great Gray Horn, the dense rock includes the longest hexagonal columns known, some over 180-meters tall. High above, the central band of the Milky Way galaxy arches across the sky. Many notable sky objects are visible, including dark strands of the Pipe Nebula and the reddish Lagoon Nebula to the tower’s right. Green grass and trees line the foreground, while clouds appear near the horizon to the tower’s left. Unlike many other international landmarks, mountaineers are permitted to climb Devils Tower.

Birthday Surprise: What picture did APOD feature on your birthday? (post 1995)

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2022 April 11

A Space Station Crosses a Busy Sun

Image Credit & Copyright: Wang Letian (Eyes at Night)

Explanation: Typically, the International Space Station is visible only at night. Slowly drifting across the night sky as it orbits the Earth, the International Space Station (ISS) can be seen as a bright spot several times a year from many locations. The ISS is then visible only just after sunset or just before sunrise because it shines by reflected sunlight — once the ISS enters the Earth’s shadow, it will drop out of sight. The only occasion when the ISS is visible during the day is when it passes right in front of the Sun. Then, it passes so quickly that only cameras taking short exposures can visually freeze the ISS’s silhouette onto the background Sun. The featured picture did exactly that — it is actually a series of images taken earlier this month from Beijing, China with perfect timing. This image series was later combined with separate images taken at nearly the same time but highlighting the texture and activity on the busy Sun. The solar activity included numerous gaseous prominences seen around the edge, highlighted in red, filaments seen against the Sun’s face, and a dark sunspot.

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2022 April 10

Shadows at the Moon’s South Pole

Image Credit: NASA, Arizona State U., Lunar Reconnaissance Orbiter

Explanation: Was this image of the Moon’s surface taken with a microscope? No — it’s a multi-temporal illumination map made with a wide-angle camera. To create it, the Lunar Reconnaissance Orbiter spacecraft collected 1,700 images over a period of 6 lunar days (6 Earth months), repeatedly covering an area centered on the Moon’s south pole from different angles. The resulting images were stacked to produce the featured map — representing the percentage of time each spot on the surface was illuminated by the Sun. Remaining convincingly in shadow, the floor of the 19-kilometer diameter Shackleton crater is seen near the map’s center. The lunar south pole itself is at about 9 o’clock on the crater’s rim. Crater floors near the lunar south and north poles can remain in permanent shadow, while mountain tops can remain in nearly continuous sunlight. Useful for future outposts, the shadowed crater floors could offer reservoirs of water-ice, while the sunlit mountain tops offer good locations to collect solar power.

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2022 April 9

Mars-Saturn Conjunction

Image Credit & Copyright: Damian Peach

Explanation: Fainter stars in the zodiacal constellation Capricornus are scattered near the plane of the ecliptic in this field of view. The two brightest ones at center aren’t stars at all though, but the planets Mars and Saturn. Taken on the morning of April 4, the telescopic snapshot captured their tantalizing close conjunction in a predawn sky, the pair of planets separated by only about 1/3 of a degree. That’s easily less than the apparent width of a Full Moon. Can you tell which planet is which? If you guessed Mars is the redder one , you’d be right. Above Mars, slightly fainter Saturn still shines with a paler yellowish tinge in reflected sunlight. Even at the low magnification, Saturn’s largest and brightest moon Titan can be spotted hugging the planet very closely on the left.

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2022 April 8

Hale-Bopp: The Great Comet of 1997

Image Credit & Copyright: Stefan Seip (TWAN)

Explanation: Only twenty-five years ago, Comet Hale-Bopp rounded the Sun and offered a dazzling spectacle in planet Earth’s night skies. Digitized from the original astrophoto on 35mm color slide film, this classic image of the Great Comet of 1997 was recorded a few days after its perihelion passage on April 1, 1997. Made with a camera and telephoto lens piggy-backed on a small telescope, the 10 minute long, hand-guided exposure features the memorable tails of Hale-Bopp, a whitish dust tail and blue ion tail. Here, the ion tail extends well over ten degrees across the northern sky. In all, Hale-Bopp was reported as visible to the naked eye from late May 1996 through September 1997. Also known as C/1995 O1, Hale-Bopp is recognized as one of the most compositionally pristine comets to pass through the inner Solar System. A visitor from the distant Oort cloud, the comet’s next perihelion passage should be around the year 4380 AD. Do you remember Hale-Bopp?

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2022 April 6

Earendel: A Star in the Early Universe

Image Credit: NASA, ESA, B. Welch (JHU), D. Coe (STScI); Processing: A. Pagan (STScI)

Explanation: Is Earendel the farthest star yet discovered? This scientific possibility started when the Hubble Space Telescope observed a huge cluster of galaxies. The gravitational lens effect of this cluster was seen to magnify and distort a galaxy far in the background. This distorted background galaxy — so far away it has a redshift of 6.2 — appears in the featured image as a long red string, while beads on that string are likely to be star clusters.   The galaxy cluster lens creates a line of maximum magnification line where superposed background objects may appear magnified many thousands of times. On the intersection between the galaxy line and the maximum magnification line is one “bead” which shows evidence of originating from a single bright star in the early universe — now named Earendel. Future investigations may include more imaging by Hubble to see how Earendel’s brightness varies, and, quite possibly, by the new James Webb Space Telescope when it becomes operational later this year.  Earendel’s great distance exceeds that of any known stable star — although the star that exploded creating GRB 090423 had a redshift of 8.2.

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2022 April 5

Seven Sisters versus California

Image Credit & Copyright: Neven Krcmarek

Explanation: On the upper right, dressed in blue, is the Pleiades. Also known as the Seven Sisters and M45, the Pleiades is one of the brightest and most easily visible open clusters on the sky. The Pleiades contains over 3,000 stars, is about 400 light years away, and only 13 light years across. Surrounding the stars is a spectacular blue reflection nebula made of fine dust. A common legend is that one of the brighter stars faded since the cluster was named. On the lower left, shining in red, is the California Nebula. Named for its shape, the California Nebula is much dimmer and hence harder to see than the Pleiades. Also known as NGC 1499, this mass of red glowing hydrogen gas is about 1,500 light years away. Although about 25 full moons could fit between them, the featured wide angle, deep field image composite has captured them both. A careful inspection of the deep image will also reveal the star forming region IC 348 and the molecular cloud LBN 777 (the Baby Eagle Nebula).

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2022 April 4

A Vortex Aurora over Iceland

Image Credit & Copyright: Christophe Suarez

Explanation: No, the car was not in danger of being vacuumed into space by the big sky vortex. For one reason, the vortex was really an aurora, and since auroras are created by particles striking the Earth from space, they do not create a vacuum. This rapidly developing auroral display was caused by a Coronal Mass Ejection from the Sun that passed by the Earth closely enough to cause a ripple in Earth’s magnetosphere. The upper red parts of the aurora occur over 250 kilometers high with its red glow created by atmospheric atomic oxygen directly energized by incoming particles. The lower green parts of the aurora occur over 100 kilometers high with its green glow created by atmospheric atomic oxygen energized indirectly by collisions with first-energized molecular nitrogen. Below 100 kilometers, there is little atomic oxygen, which is why auroras end abruptly. The concentric cylinders depict a dramatic auroral corona as seen from the side. The featured image was created from a single 3-second exposure taken in mid-March over Lake Myvatn in Iceland.

April is: Global Astronomy Month