Astronomy Picture of the Day

Jupiter’s Europa from Spacecraft Juno
Image Credit & License: NASA, JPL-Caltech, SwRI, MSSS; Processing: Andrea Luck

Explanation: What mysteries might be solved by peering into this crystal ball? In this case, the ball is actually a moon of Jupiter, the crystals are ice, and the moon is not only dirty but cracked beyond repair. Nevertheless, speculation is rampant that oceans exist under Europa‘s fractured ice-plains that could support life. Europa, roughly the size of Earth’s Moon, is pictured here in an image taken a few days ago when the Jupiter-orbiting robotic spacecraft Juno passed within 325 kilometers of its streaked and shifting surface. Underground oceans are thought likely because Europa undergoes global flexing due to its changing gravitational attraction with Jupiter during its slightly elliptical orbit, and this flexing heats the interior. Studying Juno’s close-up images may further humanity’s understanding not only of Europa and the early Solar System but also of the possibility that life exists elsewhere in the universe.

Tomorrow’s picture: big eagle

Astronomy Picture of the Day

Supernova Cannon Expels Pulsar J0002
Image Credit: F. Schinzel et al. (NRAO, NSF), Canadian Galactic Plane Survey (DRAO), NASA (IRAS);
Composition: Jayanne English (U. Manitoba)

Explanation: What could shoot out a neutron star like a cannon ball? A supernova. About 10,000 years ago, the supernova that created the nebular remnant CTB 1 not only destroyed a massive star but blasted its newly formed neutron star core — a pulsar — out into the Milky Way Galaxy. The pulsar, spinning 8.7 times a second, was discovered using downloadable software Einstein@Home searching through data taken by NASA’s orbiting Fermi Gamma-Ray Observatory. Traveling over 1,000 kilometers per second, the pulsar PSR J0002+6216 (J0002 for short) has already left the supernova remnant CTB 1, and is even fast enough to leave our Galaxy. Pictured, the trail of the pulsar is visible extending to the lower left of the supernova remnant. The featured image is a combination of radio images from the VLA and DRAO radio observatories, as well as data archived from NASA’s orbiting IRAS infrared observatory. It is well known that supernovas can act as cannons, and even that pulsars can act as cannonballs — what is not known is how supernovas do it.

Tomorrow’s picture: flyby europa

Astronomy Picture of the Day

Lunation Matrix
Image Credit & Copyright: Tunc Tezel (TWAN)

Explanation: Observe the Moon every night and you’ll see its visible sunlit portion gradually change. In phases progressing from New Moon to Full Moon to New Moon again, a lunar cycle or lunation is completed in about 29.5 days. Top left to bottom right, this 7×4 matrix of telescopic images captures the range of lunar phases for 28 consecutive nights, from the evening of July 29 to the morning of August 26, following an almost complete lunation. No image was taken 24 hours or so just after and just before New Moon, when the lunar phase is at best a narrow crescent, close to the Sun and really hard to see. Finding mostly clear Mediterranean skies required an occasional road trip to complete this lunar cycle project, imaging in early evening for the first half and late evening and early morning for the second half of the lunation. Since all the images are registered at the same scale you can use this matrix to track the change in the Moon’s apparent size during the single lunation. For extra credit, find the lunar phase that occurred closest to perigee.

Tomorrow’s picture: cosmic cannon

Astronomy Picture of the Day

Equinox Sunrise Around the World
Collage Image Copyright: Luca Vanzella

Explanation: A planet-wide collaboration resulted in this remarkable array of sunrise photographs taken around the September 2022 equinox. The images were contributed by 24 photographers, one in each of 24 nautical time zones around the world. Unlike more complicated civil time zone boundaries, the 24 nautical time zones are simply 15 degree longitude bands corresponding to 1 hour steps that span the globe. Start at the upper right for the first to experience a sunrise in the nautical time zone corresponding to Coordinated Universal Time (UTC) + 12 hours. In that time zone, the photographer was located in Christchurch, New Zealand. Travel to the west by looking down the column and then moving to the column toward the left for later sunrises as the time zone offset in hours from UTC decreases. Or, you can watch a video of September 2022 equinox sunrises around planet Earth.

Tomorrow’s picture: Observe the Moon

Astronomy Picture of the Day

DART Asteroid Impact from Space
Image Credit: ASI / NASA

Explanation: Fifteen days before impact, the DART spacecraft deployed a small companion satellite to document its historic planetary defense technology demonstration. Provided by the Italian Space Agency, the Light Italian CubeSat for Imaging Asteroids, aka LICIACube, recorded this image of the event’s aftermath. A cloud of ejecta is seen near the right edge of the frame captured only minutes following DART’s impact with target asteroid Dimorphos while LICIACube was about 80 kilometers away. Presently about 11 million kilometers from Earth, 160 meter diameter Dimorphos is a moonlet orbiting 780 meter diameter asteroid Didymos. Didymos is seen off center in the LICIACube image. Over the coming weeks, ground-based telescopic observations will look for a small change in Dimorphos’ orbit around Didymos to evaluate how effectively the DART impact deflected its target.

Tomorrow’s picture: 24 sunrises

Astronomy Picture of the Day

A Furious Sky over Mount Shasta
Image Credit & Copyright: Ralf Rohner

Explanation: Is the sky angry with Mount Shasta? According to some ancient legends, the spirits of above and below worlds fight there, sometimes quite actively during eruptions of this enormous volcano in California, USA. Such drama can well be imagined in this deep sky image taken in late June. Evident above the snow-covered peak is the central band of our Milky Way Galaxy, on the left, and a picturesque sky toward the modern constellations of Scorpius and Ophiuchus, above and to the right. The bright orange star Antares and the colorful rho Ophiuchi cloud complex are visible just to the right of Mount Shasta, while the red emission nebula surrounding the star zeta Ophiuchi appears on the top right. The static earth image in the featured composite was taken during the blue hour, while a two-panel panorama tracking the background sky was taken later that night with the same camera and from the same location. Within a few million years, Antares, some stars in the rho Ophiuchi system, and zeta Ophiuchi will all likely explode as supernovas.

Tomorrow’s picture: asteroid safety

Astronomy Picture of the Day

DART: Impact on Asteroid Dimorphos
Video Credit: NASA, JHUAPL, DART

Explanation: Could humanity deflect an asteroid headed for Earth? Yes. Deadly impacts from large asteroids have happened before in Earth‘s past, sometimes causing mass extinctions of life. To help protect our Earth from some potential future impacts, NASA tested a new planetary defense mechanism yesterday by crashing the robotic Double Asteroid Redirection Test (DART) spacecraft into Dimorphos, a small asteroid spanning about 170-meters across. As shown in the featured video, the impact was a success. Ideally, if impacted early enough, even the kick from a small spacecraft can deflect a large asteroid enough to miss the Earth. In the video, DART is seen in a time-lapse video first passing larger Didymos, on the left, and then approaching the smaller Dimorphos. Although the video ends abruptly with DART’s crash, observations monitoring the changed orbit of Dimorphos — from spacecraft and telescopes around the world — have just begun.

Tomorrow’s picture: furious sky

Astronomy Picture of the Day

All the Water on Planet Earth
Illustration Credit: Jack Cook, Adam Nieman, Woods Hole Oceanographic Institution; Data source: Igor Shiklomanov

Explanation: How much of planet Earth is made of water? Very little, actually. Although oceans of water cover about 70 percent of Earth’s surface, these oceans are shallow compared to the Earth’s radius. The featured illustration shows what would happen if all of the water on or near the surface of the Earth were bunched up into a ball. The radius of this ball would be only about 700 kilometers, less than half the radius of the Earth’s Moon, but slightly larger than Saturn’s moon Rhea which, like many moons in our outer Solar System, is mostly water ice. The next smallest ball depicts all of Earth‘s liquid fresh water, while the tiniest ball shows the volume of all of Earth’s fresh-water lakes and rivers. How any of this water came to be on the Earth and whether any significant amount is trapped far beneath Earth‘s surface remain topics of research.

Tomorrow’s picture: furious sky

Astronomy Picture of the Day

The Fairy of Eagle Nebula
Image Credit: Image Credit: NASA, ESA, The Hubble Heritage Team (STScI/AURA)

Explanation: The dust sculptures of the Eagle Nebula are evaporating. As powerful starlight whittles away these cool cosmic mountains, the statuesque pillars that remain might be imagined as mythical beasts. Featured here is one of several striking dust pillars of the Eagle Nebula that might be described as a gigantic alien fairy. This fairy, however, is ten light years tall and spews radiation much hotter than common fire. The greater Eagle Nebula, M16, is actually a giant evaporating shell of gas and dust inside of which is a growing cavity filled with a spectacular stellar nursery currently forming an open cluster of stars. This great pillar, which is about 7,000 light years away, will likely evaporate away in about 100,000 years. The featured image is in scientifically re-assigned colors and was taken by the Earth-orbiting Hubble Space Telescope.

Tomorrow’s picture: earth without water

Astronomy Picture of the Day

September Sunrise Shadows
Image Credit & Copyright: Donato Lioce

Explanation: The defining astronomical moment for this September’s equinox was on Friday, September 23, 2022 at 01:03 UTC, when the Sun crossed the celestial equator moving south in its yearly journey through planet Earth’s sky. That marked the beginning of fall for our fair planet in the northern hemisphere and spring in the southern hemisphere, when day and night are nearly equal around the globe. Of course, if you celebrate the astronomical change of seasons by watching a sunrise you can also look for crepuscular rays. The shadows cast by clouds can have a dramatic appearance in the twilight sky during any sunrise or sunset. Due to perspective, the parallel shadows will seem to point back to the rising Sun and a place due east on your horizon near the equinox date. Taken on September 15, this sunrise sea and skyscape captured crepuscular rays in the sky and watery specular reflections from the Mediterranean coast near the village of Petacciato, Italy.

Tomorrow’s picture: shadows of cosmic dust