Astronomy Picture of the Day
Explanation: What would it look like to fly over the North Pole of Jupiter? A fictional animation made from real images and data captured by NASA’s Juno spacecraft shows an answer. Since the pole is presently in shadow, the video uses infrared light emitted by Jupiter — specifically an infrared color where the hottest features glows the brightest. As the animation starts, Juno zooms in on the enormous world. Soon, one of the eight cyclones orbiting the North Pole is featured. One by one, all eight cyclones circling the pole are inspected, each the size of an entire continent on Earth, and each containing bumpy and fragmented spiral walls. The virtual trip ends with a zoom out. Studying Jovian cyclones helps humanity to better understanddangerous storm systems that occur here on Earth. Juno has recently concluded another close pass by Jupiter — Perijove 12 — and seems healthy enough to complete several more of the two-month orbits.
Space Shuttle Rising
Image Credit: NASA
Explanation: What’s that rising from the clouds? The space shuttle. Sometimes, if you look out the window of an airplane at just the right time and place, you see something unusual — in this case a space shuttle launching to orbit. The featured image of Endeavour’s final launch in 2011 May was captured from a NASA shuttle training aircraft. Taken well above the clouds, the image can be matched with similar images of the same shuttle plume taken below the clouds. Hot glowing gasses expelled by the engines are visible near the rising shuttle, as well as a long smoke plume. A shadow of the plume appears on the cloud deck, indicating the direction of the Sun. The US Space Shuttle program concluded in 2011, and Endeavour can now be visited at the California Science Center. Planned for tomorrow, however, is a different launch — that of the Transiting Exoplanet Survey Satellite (TESS) aboard a SpaceX Falcon 9 rocket.
Explanation: Deep shadows create dramatic contrasts between light and dark in this high-resolution close-up of the martian surface. Recorded on January 24, 2014 by the HiRISE camera onboard the Mars Reconnaissance Orbiter, the scene spans about 1.5 kilometers. From 250 kilometers above the Red Planet the camera is looking down at a sand dune field in a southern highlands crater. Captured when the Sun was about 5 degrees above the local horizon, only the dune crests were caught in full sunlight. A long, cold winter is coming to the southern hemisphere and bright ridges of seasonal frost line the martian dunes.
Explanation: From our vantage point in the Milky Way Galaxy, we see NGC 3344 face-on. Nearly 40,000 light-years across, the big, beautiful spiral galaxy is located just 20 million light-years away in the constellation of Leo Minor. This multi-color Hubble Space Telescope close-up of NGC 3344 includes remarkable details from near infrared to ultraviolet wavelengths. The frame extends some 15,000 light-years across the spiral’s central regions. From the core outward, the galaxy’s colors change from the yellowish light of old stars in the center to young blue star clusters and reddish star forming regions along the loose, fragmented spiral arms. Of course, the bright stars with a spiky appearance are in front of NGC 3344 and lie well within our own Milky Way.
Explanation: Wandering through the constellation Sagittarius, bright planets Mars and Saturn appeared together in early morning skies over the last weeks. They are captured in this 3 degree wide field-of-view from March 31 in a close celestial triangle with large globular star cluster Messier 22. Of course M22 (bottom left) is about 10,000 light-years distant, a massive ball of over 100,000 stars much older than our Sun. Pale yellow and shining by reflected sunlight, Saturn (on top) is about 82 light-minutes away. Look carefully and you can spot large moon Titan as a pinpoint of light at about the 5 o’clock position in the glare of Saturn’s overexposed disk. Slightly brighter and redder Mars is 9 light-minutes distant. While both planets are moving on toward upcoming oppositions, by July Mars will become much brighter still, with good telescopic views near its 2018 opposition. Then it will be a mere 3.2 light-minutes from planet Earth.
Explanation: Was this flash the farthest star yet seen? An unexpected flash of light noticed fortuitously on Hubble Space Telescope images may prove to be not only an unusual gravitational lensing event but also an image of a normal star 100 times farther away than any star previously imaged individually. The featured image shows the galaxy cluster on the left complete with many yellowish galaxies, while on the right is an expanded square where a source appeared in 2016 that was not evident in 2011. The spectrum and variability of this source are strangely unlike a supernova, but rather appear more consistent with a normal blue supergiant star magnified by about a factor of 2000 by a confluence of aligned gravitational lenses. Dubbed Icarus, the source is in a galaxy well behind the galaxy cluster and far across the universe — at redshift 1.5. If the lens interpretation is correct and Icarus is not an exploding star, further observations of it and other similarly magnified stars could give information about the stellar and dark matter content in the galaxy cluster and the universe.
Dragon Aurora over Norway
Image Credit & Copyright: Marco Bastoni
Explanation: What’s that in the sky? An aurora. A large coronal hole opened last month, a few days before this image was taken, throwing a cloud of fast moving electrons, protons, and ionstoward the Earth. Some of this cloud impacted our Earth’s magnetosphere and resulted in spectacular auroras being seen at high northern latitudes. Featured here is a particularly photogenicauroral curtain captured above Tromsø Norway. To the astrophotographer, this shimmering green glow of recombining atmospheric oxygen appeared as a large dragon, but feel free to sharewhat it looks like to you. Although now past Solar Maximum, our Sun continues to show occasional activity creating impressive auroras on Earth visible even last week.
Explanation: One of the most spectacular solar sights is an explosive flare. In 2011 June, the Sun unleashed somewhat impressive, medium-sized solar flare as rotation carried active regions of sunpots toward the solar limb. That flare, though, was followed by an astounding gush of magnetized plasma — a monster filament seen erupting at the Sun’s edge in this extreme ultraviolet image from NASA’s Solar Dynamics Observatory. Featured here is a time-lapse video of that hours-long event showing darker, cooler plasma raining down across a broad area of the Sun’s surface, arcing along otherwise invisible magnetic field lines. An associated coronal mass ejection, a massive cloud of high energy particles, was blasted in the general direction of theEarth,and made a glancing blow to Earth’s magnetosphere.
AE Aurigae and the Flaming Star Nebula
Image Credit & Copyright: Martin Pugh
Explanation: Why is AE Aurigae called the flaming star? For one reason, the surrounding nebula IC 405 is named the Flaming Star Nebula because the region seems to harbor smoke, even though nothing is on fire, including interior star AE Aurigae. Fire, typically defined as the rapid molecular acquisition of oxygen, happens only when sufficient oxygen is present and is not important in such high-energy, low-oxygen environments. The material that appears as smoke is mostly interstellar hydrogen, but does contain smoke-like dark filaments of carbon-rich dust grains. The bright star AE Aurigae is visible near the nebula center and is so hot it is blue, emitting light so energetic it knocks electrons away from atoms in the surrounding gas. When an atom recaptures an electron, light is emitted creating the surrounding emission nebula. The Flaming Star nebula lies about 1,500 light years distant, spans about 5 light years, and is visible with a small telescope toward the constellation ofthe Charioteer (Auriga).
Explanation: Stars of the Hyades cluster are scattered through this mosaic spanning over 5 degrees on the sky toward the constellation Taurus. Presently cruising through the Solar System, the remarkably blue cometC/2016 R2 PanSTARRS is placed in the wide field of view using image data from January 12. With the apex of the V-shape in the Hyades cluster positioned near the top center, bright Aldebaran, alpha star of Taurus, anchors the frame at the lower right. A cool red giant, Aldebaran is seen in orange hues in the colorful starfield. While the stars of the Hyades are gathered 151 light-years away, Aldebaran lies only 65 light-years distant and so is separate from the cluster stars. On January 12, C/2016 R2 was over 17 light-minutes from planet Earth and nearly 24 light-minutes from the Sun. Its blue tinted tail largely due to CO+ gas fluorescing in sunlight, the head or coma of the comet appears with a slightly greenish hue, likely emission from diatomic carbon.
Explanation: With image data from telescopes large and small, this close-up features the dusty Elephant’s Trunk Nebula. It winds through the emission nebula and young star cluster complex IC 1396, in the high and far off constellation of Cepheus. Also known as vdB 142, the cosmic elephant’s trunk is over 20 light-years long. The colorful view highlights bright, swept-back ridges that outline the region’s pockets of cool interstellar dust and gas. Such embedded, dark, tendril-shaped clouds contain the raw material for star formation and hide protostars within. Nearly 3,000 light-years distant, the relatively faint IC 1396 complex covers a large region on the sky, spanning over 5 degrees. This dramatic scene spans a 1 degree wide field, about the size of 2 Full Moons.
Explanation: The Crab Nebula is cataloged as M1, the first on Charles Messier’s famous list of things which are not comets. In fact, the Crab is now known to be a supernova remnant, an expanding cloud of debris from the explosion of a massive star. The violent birth of the Crab was witnessed by astronomers in the year 1054. Roughly 10 light-years across today, the nebula is still expanding at a rate of over 1,000 kilometers per second. Over the past decade, its expansion has been documented in this stunning time-lapse movie. In each year from 2008 to 2017, an image was produced with the same telescope and camera from a remote observatory in Austria. Combined in the time-lapse movie, the 10 images represent 32 hours of total integration time. The sharp, processed frames even reveal the dynamic energetic emission within the incredible expanding Crab. The Crab Nebula lies about 6,500 light-years away in the constellation Taurus.
Explanation: Will our Sun look like this one day? The Helix Nebula is one of brightest and closest examples of a planetary nebula, a gas cloud created at the end of the life of a Sun-like star. The outer gasses of the starexpelled into space appear from our vantage point as if we are looking down a helix. The remnant central stellar core, destined to become a white dwarf star, glows in light so energetic it causes the previously expelled gas to fluoresce. The Helix Nebula, given a technical designation of NGC 7293, lies about 700 light-years away towards the constellation of the Water Bearer (Aquarius) and spans about 2.5 light-years. The featured picturewas taken with the Canada-France-Hawaii Telescope (CFHT) located atop a dormant volcano in Hawaii, USA. A close-up of the inner edge of the Helix Nebula shows complex gas knots of unknown origin.
Unexpected X-Rays from Perseus Galaxy Cluster
Image Credit: X-ray: NASA/CXO/Oxford University/J. Conlon et al.; Radio: NRAO/AUI/NSF/Univ. of Montreal/Gendron-Marsolais et al.; Optical: NASA/ESA/IoA/A. Fabian et al.; DSS
Explanation: Why does the Perseus galaxy cluster shine so strangely in one specific color of X-rays? No one is sure, but a much-debated hypothesis holds that these X-rays are a clue to the long-sought identity of dark matter. At the center of this mystery is a 3.5 Kilo-electronvolt (KeV) X-ray color that appears to glow excessively only when regions well outside the cluster center are observed, whereas the area directly surrounding a likely central supermassive black hole is actually deficient in 3.5 keV X-rays. One proposed resolution — quite controversial — is that something never seen before might be present: fluorescent dark matter (FDM). This form of particle dark matter might be able to absorb 3.5 keV X-radiation. If operating, FDM, after absorption, might later emit these X-rays from all over the cluster, creating an emission line. However, when seensuperposed in front of the central region surrounding the black hole, FDM’s absorption would be more prominent, creating an absorption line. Pictured, a composite image of the Perseus galaxy cluster shows visible and radio light in red, and X-ray light from the Earth-orbiting Chandra Observatory in blue.
Explanation: What’s happened to the Sun? Sometimes it looks like the Sun is being viewed through a giant lens. In the featured video, however, there are actually millions of tiny lenses: ice crystals. Water may freeze in the atmosphere into small, flat, six-sided, ice crystals. As these crystals flutter to the ground, much time is spent with their faces flat and parallel to the ground. An observer may find themselves in the same plane as many of the falling ice crystals near sunrise or sunset. During this alignment, each crystal can act like a miniature lens, refracting sunlight into our view and creating phenomena like parhelia, the technical term for sundogs. Thefeatured video was taken a month ago on the side of a ski hill at the Vemdalen Ski Resort in central Sweden. Visible in the center is the most direct image of the Sun, while two bright sundogs glow prominently from both the left and the right. Also visible is the bright 22 degree halo — as well as the rarer and much fainter 46 degree halo — also created by sunlight reflecting off of atmospheric ice crystals.
Explanation: Galaxies are fascinating not only for what is visible, but for what is invisible. Grand spiral galaxy NGC 1232, captured in detail by one of the Very Large Telescopes, is a good example. The visible is dominated by millions of bright stars and dark dust, caught up in a gravitational swirl of spiral arms revolving about the center. Open clusters containing bright blue stars can be seen sprinkled along these spiral arms, while dark lanes of dense interstellar dust can be seen sprinkled between them. Less visible, but detectable, are billions of dim normal stars and vast tracts of interstellar gas, together wielding such high mass that they dominate the dynamics of the inner galaxy. Leading theories indicate that even greater amounts of matter are invisible, in a form we don’t yet know. This pervasive dark matter is postulated, in part, to explain the motions of the visible matter in the outer regions of galaxies.
Explanation: Why is there a spiral around the North Pole of Mars? Each winter this pole develops a new outer layer about one meter thick composed of carbon dioxide frozen out of the thin Martian atmosphere. This fresh layer is deposited on a water-ice layer that exists year round. Strong winds blow down from above the cap’s center and swirl due to the spin of the red planet — contributing to Planum Boreum‘s spiral structure. The featured image is a perspective mosaic generated earlier this year from numerous images taken by ESA’s Mars Express and elevations extracted from the laser altimeter aboard NASA’s Mars Global Surveyor mission. New missions to Mars planned in the next few years include Insight with plans to drill into Mars, and ExoMars and the Mars 2020 Rover with plans to search for signs of microscopic Martian life — past and present.
The Kepler-90 Planetary System
Illustration Credit: NASA Ames, Wendy Stenzel
Explanation: Do other stars have planetary systems like our own? Yes — one such system is Kepler-90. Cataloged by the orbiting Kepler satellite, an eighth planet has now been discovered giving Kepler-90 the same number of known planets as our Solar System. Similarities between Kepler-90 and our system include a G-type star comparable to our Sun, rocky planets comparable to our Earth, and large planets comparable in size to Jupiter and Saturn. Differences include that all of the known Kepler-90 planets orbit relatively close in — closer than Earth’s orbit around the Sun — making them possibly too hot to harbor life. However, observations over longer time periods may discover cooler planets further out. Kepler-90 lies about 2,500 light years away, and at magnitude 14 is visible with a medium-sized telescope toward the constellation of the Dragon (Draco). Exoplanet-finding missions planned for launch in the next decade include TESS, JWST, WFIRST, and PLATO.
Explanation: In December of 1972, Apollo 17 astronauts Eugene Cernan and Harrison Schmitt spent about 75 hours on the Moon in the Taurus-Littrow valley, while colleague Ronald Evans orbited overhead. This sharp image was taken by Cernan as he and Schmitt roamed the valley floor. The image shows Schmitt on the left with the lunar rover at the edge of Shorty Crater, near the spot where geologist Schmitt discovered orange lunar soil. The Apollo 17 crew returned with 110 kilograms of rock and soil samples, more than was returned from any of the other lunar landing sites. Forty five years later, Cernan and Schmitt are still the lastto walk on the Moon.
Explanation: Yes, but have you ever taken a selfie on Mars? The Curiosity rover on Mars has. This selfie was compiled from many smaller images — which is why the mechanical arm holding the camera is not visible. (Although its shadow is!) Taken in mid-2015, the featured image shows not only the adventurous rover, but dark layered rocks, the light colored peak of Mount Sharp, and the rusting red sand that pervades Mars. If you look closely, you can even see that a small rock is stuck into one of Curiosity’s aging wheels. Now nearing the end of 2017, Curiosity continues to explore the layers of sedimentary rocks it has discovered on Vera Rubin Ridge in order to better understand, generally, the ancient geologic history of Mars and, specifically, why these types of rocks exist there.
The Comet and the Star Cluster
Explanation: Comet Linear has become unexpectedly bright. The comet, discovered in 2000, underwent a 100-fold outburst just a week before it passed a mere 14 lunar distances from Earth late last month. The comet was captured here last week at about magnitude 6 — just bright enough to be seen by the unaided eye — passing in front of the distant globular star clusterM14. Comet 252/P LINEAR is one of a rare group of comets that vacillate between the Earth and Jupiter every 5 years. How the comet will evolve from here is unknown, but hopes run high that it will remain a good object for binoculars in northern skies for the next week or two.
A Green Flash of Spring
Explanation: Taken on March 20 from the top of Haleakala on the isle of Maui, planet Earth, the first sunrise of northern spring is pictured in this vacation snapshot. The telephoto view from the volcanic caldera above a sea of clouds also captures an elusive green flash near the Sun’s upper limb. Atmospheric layers with sharp temperature changes cause the colorful flash as the Sun rises behind a distant cloud bank. Refraction along sight lines through the layers creates multiple distorted images of the Sun, and for a moment, can visibly deflect shorter wavelength green light.