[{"date":"1998-07-24","explanation":"On another Friday (May 5, 1961), at the dawn of the space age, NASA controllers \"lit the candle\" and sent Alan B. Shepard Jr. arcing into space atop a Redstone rocket. The picture shows the pressure-suited Shepard before the launch in his cramped space capsule dubbed \"Freedom 7\" . This historic flight - the first spaceflight by an American - made Shepard a national hero. Born in East Derry, New Hampshire on November 18, 1923, Shepard graduated from the United States Naval Academy in 1944 and went on to train and serve as a Naval Aviator. Chosen as one of the original seven Mercury Program astronauts, he considered this first flight the greatest challenge and actively sought the assignment. Shepard's accomplishments in his career as an astronaut spanned a remarkable period in human achievement and in 1972 he walked on the moon as commander of the Apollo 14 mission. A true pioneer and intrepid explorer, Alan Shepard died Tuesday at age 74 after a lengthy illness.","hdurl":"https://apod.nasa.gov/apod/image/9807/shepard_freedom7_big.jpg","media_type":"image","service_version":"v1","title":"Alan B. Shepard Jr. 1923-1998","url":"https://apod.nasa.gov/apod/image/9807/shepard_freedom7.jpg"},{"copyright":"Fabian Neyer","date":"2020-12-04","explanation":"A bright spiral galaxy of the northern sky, Messier 63 is nearby, about 30 million light-years distant toward the loyal constellation Canes Venatici. Also cataloged as NGC 5055, the majestic island universe is nearly 100,000 light-years across, about the size of our own Milky Way. Its bright core and majestic spiral arms lend the galaxy its popular name, The Sunflower Galaxy, while this exceptionally deep exposure also follows faint, arcing star streams far into the galaxy's halo. Extending nearly 180,000 light-years from the galactic center the star streams are likely remnants of tidally disrupted satellites of M63. Other satellite galaxies of M63 can be spotted in this remarkable wide-field image, made with a small telescope, including five newly identified faint dwarf galaxies, which could contribute to M63's star streams in the next few billion years.","hdurl":"https://apod.nasa.gov/apod/image/2012/Neyerm63_l2.jpg","media_type":"image","service_version":"v1","title":"Curly Spiral Galaxy M63","url":"https://apod.nasa.gov/apod/image/2012/Neyerm63_l1_1024.jpg"},{"date":"2002-09-27","explanation":"Don't be fooled by the familiar symmetry. The graceful spiral structure seen in this computer visualization does not portray winding spiral arms in a distant galaxy of stars. Instead, the graphic shows spiral shock waves in a three dimensional simulation of an accretion disk -- material swirling onto a compact central object that could represent a white dwarf star, neutron star, or black hole. Such accretion disks power bright x-ray sources within our own galaxy. They form in binary star systems which consist of a donor star (not shown above), supplying the accreting material, and a compact object whose strong gravity ultimately draws the material towards its surface. For known x-ray binary systems the size of the accretion disk itself might fall somewhere between the diameter of the Sun (about 1,400,000 kilometers) and the diameter of the Moon's orbit (800,000 kilometers). One interesting result of the virtual reality astrophysics illustrated here is that the simulated disk develops instabilities which tend to smear out the pronounced spiral shocks.","hdurl":"https://apod.nasa.gov/apod/image/0209/accretion_mpowen_full.jpg","media_type":"image","service_version":"v1","title":"Accretion Disk Simulation","url":"https://apod.nasa.gov/apod/image/0209/accretion_mpowen_c1.jpg"},{"copyright":"Vikas Chander, \nH.E.S.S. Collaboration;\n Music:  Emotive Piano by \nImmersive Music","date":"2019-01-08","explanation":"They may look like modern mechanical dinosaurs but they are enormous swiveling eyes that watch the sky. The High Energy Stereoscopic System (H.E.S.S.) Observatory is composed of four 12-meter reflecting-mirror telescopes surrounding a larger telescope housing a 28-meter mirror. They are designed to detect strange flickers of blue light -- Cherenkov radiation --emitted when charged particles move slightly faster than the speed of light in air.  This light is emitted when a gamma ray from a distant source strikes a molecule in Earth's atmosphere and starts a charged-particle shower.  H.E.S.S. is sensitive to some of the highest energy photons (TeV) crossing the universe.  Operating since 2003 in Namibia, H.E.S.S. has searched for dark matter and has discovered over 50 sources emitting high energy radiation including supernova remnants and the centers of galaxies that contain supermassive black holes.  Pictured last September, H.E.S.S. telescopes swivel and stare in time-lapse sequences shot in front of our Milky Way Galaxy and the Magellanic Clouds -- as the occasional Earth-orbiting satellite zips by.   Open Science: Browse 1,800+ codes in the Astrophysics Source Code Library","media_type":"video","service_version":"v1","title":"HESS Telescopes Explore the High-Energy Sky","url":"https://www.youtube.com/embed/iRL268cXaqk?rel=0"},{"date":"2004-08-27","explanation":"The discovery of Sedna (aka 2003 VB12), the most distant known object orbiting the Sun, presents a mystery. Pluto's orbit averages about 40 AU in radius, where an AU (Astronomical Unit) is the Earth-Sun distance. But the closest point in Sedna's eccentric orbit scarcely comes within 75 AU, while its farthest point extends to nearly 1,000 AU. So how did something as large as Sedna get so far out there? Exploring the problem with computer simulations, astronomers Alessandro Morbidelli and Harold Levison suggest that while Sedna was not formed in its current location, it was also not moved there by encounters with other solar system objects. Instead, they find it more likely that Sedna resides in its present orbit because of an encounter with another star. In one scenario, objects like Sedna are yanked out of closer orbits by the gravitational pull of a Sun-sized star passing near the solar system during its formative years. Alternatively Sedna could have formed of material from another system entirely, captured during an early encounter with a much smaller star. Both Sedna-forming stellar encounter scenarios are consistent with idea that the Sun itself was born in an ancient, dense, cluster of stars.","hdurl":"https://apod.nasa.gov/apod/image/0408/Sedna_Comparison.jpg","media_type":"image","service_version":"v1","title":"The Sedna Scenario","url":"https://apod.nasa.gov/apod/image/0408/Sedna_Comparison_sm.jpg"},{"date":"2022-11-04","explanation":"The Mars InSight lander returned its first image from the Red Planet's flat, equatorial Elysium Planitia after a successful touchdown on November 26, 2018. The history making mission to explore the martian Interior using Seismic investigations, geodesy, and heat transport has been operating for over 1,400 martian days or sols. In that time the InSight mission has detected more than 1,300 marsquakes and recorded data from Mars-shaking meteoroid impacts, observing how the seismic waves travel to provide a glimpse inside Mars. Analyzing the archive of data collected is expected to yield discoveries for decades. But InSight's final operational sol is likely not far off. The reason is evident in this selfie recorded earlier this year showing its deck and large, 2-meter-wide solar panels covered with dust. Kicked up by martian winds the dust continues to accumulate and drastically reduce the power that can be generated by InSight's solar panels.","hdurl":"https://apod.nasa.gov/apod/image/2211/PIA25287_insight.jpg","media_type":"image","service_version":"v1","title":"InSight's Final Selfie","url":"https://apod.nasa.gov/apod/image/2211/PIA25287_insight1024.jpg"},{"date":"2013-11-25","explanation":"How far away is spiral galaxy NGC 4921? Although presently estimated to be about 310 million light years distant, a more precise determination could be coupled with its known recession speed to help humanity better calibrate the expansion rate of the entire visible universe.  Toward this goal, several images were taken by the Hubble Space Telescope in order to help identify key stellar distance markers known as Cepheid variable stars.   Since NGC 4921 is a member of the Coma Cluster of Galaxies, refining its distance would also allow a better distance determination to one of the largest nearby clusters in the local universe. The magnificent spiral NGC 4921 has been informally dubbed anemic because of its low rate of star formation and low surface brightness. Visible in the above image are, from the center, a bright nucleus, a bright central bar, a prominent ring of dark dust, blue clusters of recently formed stars, several smaller companion galaxies, unrelated galaxies in the far distant universe, and unrelated stars in our Milky Way Galaxy.    Free lecture: APOD editor to speak in NYC on Jan. 3","hdurl":"https://apod.nasa.gov/apod/image/1311/ngc4921_colombari_3984.jpg","media_type":"image","service_version":"v1","title":"Anemic Spiral NGC 4921 from Hubble","url":"https://apod.nasa.gov/apod/image/1311/ngc4921_colombari_960.jpg"},{"copyright":"Steven Mohr","date":"2020-10-28","explanation":"Why is the Lobster Nebula forming some of the most massive stars known? No one is yet sure.  Cataloged as NGC 6357, the Lobster Nebula houses the open star cluster Pismis 24 near its center -- a home to unusually bright and massive stars.  The overall blue glow near the inner star forming region results from the emission of ionized hydrogen gas.   The surrounding nebula, featured here, holds a complex tapestry of gas, dark dust, stars still forming, and newly born stars.  The intricate patterns are caused by complex interactions between interstellar winds, radiation pressures, magnetic fields, and gravity.  NGC 6357 spans about 400 light years and lies about 8,000 light years away toward the constellation of the Scorpion.","hdurl":"https://apod.nasa.gov/apod/image/2010/Lobster_Mohr_2048.jpg","media_type":"image","service_version":"v1","title":"NGC 6357: The Lobster Nebula","url":"https://apod.nasa.gov/apod/image/2010/Lobster_Mohr_1080.jpg"},{"copyright":"C. Conselice","date":"2005-07-25","explanation":"How were the unusual gas filaments surrounding galaxy NGC 1275 created?  No one is sure. Galaxy NGC 1275 is the central dominant galaxy of the Perseus Cluster of Galaxies, a cluster with many member galaxies visible in the above image.  In visible light, NGC 1275 appears to show a spectacular collision between two distinct galaxies.  The galaxy and cluster are also bright emitters of X-rays.  The unusual gas filaments are shown above in a very specific color of light emitted by hydrogen, here artificially colored pink.  Possible origins for the filaments may involve details of the collision between the two galaxies, or alternatively, interactions between a galactic center black hole and the surrounding intracluster gas.  NGC 1275, pictured above, spans about 100,000 light years and lies about 230 million light years distant toward the constellation of Perseus.","hdurl":"https://apod.nasa.gov/apod/image/0507/ngc1275_wiyn_big.jpg","media_type":"image","service_version":"v1","title":"Unusual Gas Filaments Surround Galaxy NGC 1275","url":"https://apod.nasa.gov/apod/image/0507/ngc1275_wiyn.jpg"},{"copyright":"Wei-Hao Wang \n(IfA, U. Hawaii)","date":"2006-05-10","explanation":"Portuguese navigator Fernando de Magellan and his crew had plenty of time to study the southern sky during the first circumnavigation of planet Earth. As a result, two fuzzy cloud-like objects easily visible for southern hemisphere skygazers are known as the Clouds of Magellan. Of course, these star clouds are now understood to be dwarf irregular galaxies, satellites of our larger spiral Milky Way galaxy. The Large Magellanic Cloud (LMC) pictured above is only about 180,000 light-years distant in the constellation Dorado. Spanning about 15,000 light-years or so, it is the most massive of the Milky Way's satellite galaxies and is the site of the closest supernova in modern times.  The prominent red knot on the left is 30 Doradus, or the Tarantula Nebula, a giant star-forming region in the Large Magellanic Cloud.","hdurl":"https://apod.nasa.gov/apod/image/0605/lmc_whw_big.jpg","media_type":"image","service_version":"v1","title":"The Large Cloud of Magellan","url":"https://apod.nasa.gov/apod/image/0605/lmc_whw.jpg"}]