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A Comet-Hunter's Legacy -- The Messier Catalog (Also see The Messier Catalog: Nebulae / Open Clusters / Globular Clusters / Galaxies) In 1758, Charles Messier, a young French astronomer, was trying to find the comet which Edmond Halley had predicted would return in that year -- the comet we now know as Halley's Comet. While hunting for the comet, he happened across a small fuzzy patch in Taurus which looked, in a small telescope, just like a comet, but did not move among the stars from night to night, as comets do. This fuzzy patch had already been discovered by John Bevis, in 1731, but became most famous as M1, the first item in a list which Messier began to compile, of faint fuzzy objects which might be mistaken for comets. Messier eventually observed forty-four comets, of which thirteen were independent discoveries, and twelve carry his name, in recognition of the discovery, so he was an exceptionally successful comet-hunter. Nowadays, however, what he is most remembered for is the list of faint fuzzy objects, the Messier Catalog, which he constructed. The objects on this list represent the majority of the easily observable dark-sky objects visible from northern latitudes, and include many of the most beautiful objects in the heavens. Images of all the Messier Catalog objects, including some added after his death. (P. Gitto, apod000311) M1 -- The Crab Nebula A supernova remnant in Taurus. (Walter Nowotny (U. Wien, Nordic Optical Telescope, apod050920) M8 -- The Lagoon Nebula An emission nebula in Sagittarius (N. A. Sharp, REU Program, AURA, NOAO, NSF, apod021006) M17 -- The Omega Nebula An emission nebula in Sagittarius (B. Wallis and R. Provin, apod960829) M20 -- The Trifid Nebula An emission nebula in Sagittarius (Todd Boroson, AURA, NOAO, NSF, apod000328) M27 -- The Dumbbell Nebula A planetary nebula in Vulpecula (Joe & Gail Metcalf, Adam Block, NOAO, AURA, NSF, apod050603) M42 -- The Orion Nebula An emission nebula in Orion (NASA, ESA, M. Robberto (STScI/ESA) and The Hubble Space Telescope Orion Treasury Project Team, apod060119) M43 A portion of the Orion nebula separated from the main portion by a dark lane. (On the lower left, in the above image of M42) (NASA, ESA, M. Robberto (STScI/ESA) and The Hubble Space Telescope Orion Treasury Project Team, apod060119) M57 -- The Ring Nebula A planetary nebula in Lyra, 2000 light years away (H. Bond et al., Hubble Heritage Team (STScI / AURA), NASA, apod030322) M76 A planetary nebula in Perseus (Stefan Seip, apod061102) M78 A reflection nebula in Orion (Stephan Messner, apod051104) M97 -- The Owl Nebula A planetary nebula in Ursa Major (AURA, NSF, NOAO) The Messier Catalog: Globular Clusters M2 A globular cluster in Aquarius (D. Williams, N. A. Sharp, AURA, NOAO, NSF, apod010611) M3 A globular cluster in Canes Venatici (S. Kafka & K. Honeycutt (Indiana University), WIYN, NOAO, NSF, apod060312) M4 A globular cluster in Scorpius, the closest to us, at 7000 light years (T2KA, KPNO 0.9-m Telescope, NOAO, AURA, NSF, apod000523) M5 A globular cluster in Serpens Caput, one of the most massive in our galaxy (AURA, NSF, NOAO) M9 A globular cluster in Ophiuchus (AURA, NSF, NOAO) M10 A globular cluster in Ophiuchus (Till Credner, Sven Kohle (Bonn University), Hoher List Observatory, apod010630) M12 A globular cluster in Ophiuchus (Alan and Lynn Gingrich, Adam Block, AURA, NSF, NOAO) M13 -- The Globular Cluster in Hercules A globular cluster in Hercules (Eddie Guscott, apod040511) M14 A globular cluster in Ophiuchus (AURA, NSF, NOAO) M15 A globular cluster in Pegasus (H. Bond et al., Hubble Heritage Team (STScI / AURA), NASA, apod000804) M19 A globular cluster in Ophiuchus (D. Williams, N. A. Sharp, AURA, NOAO, NSF, apod000719) M22 A globular cluster in Sagittarius (Jean-Charles Cuillandre (CFHT), Hawaiian Starlight, CFHT, apod050627) M28 A globular cluster in Sagittarius (AURA, NSF, NOAO) M30 A globular cluster in Capricornus (REU program, AURA, NSF, NOAO) M53 A globular cluster in Coma Berenices (Bill Keel, University of Alabama, Kitt Peak National Observatory; obtained from SEDS site) M54 A globular cluster in Sagittarius (REU Program, AURA, NSF, NOAO) M55 A globular cluster in Sagittarius (B.J. Mochejska, J. Kaluzny (CAMK), 1m Swope Telescope, apod000922) M56 A globular cluster in Lyra (AURA, NSF, NOAO) M62 A globular cluster in Ophiuchus (false-color infrared (two micron) image, 2MASS (University of Massachusetts); image obtained from SEDS site) M68 A globular cluster in Hydra (AURA, NSF, NOAO) M69 A globular cluster in Sagittarius (REU program, AURA, NSF, NOAO) M70 A globular cluster in Sagittarius (REU program, AURA, NSF, NOAO) M71 A globular cluster in Sagitta (T. Credner, S. Kohle, University of Bonn; obtained from SEDS site) M72 A globular cluster in Aquarius (Bill Keel, University of Alabama, Kitt Peak National Observatory; obtained from SEDS site) M75 A globular cluster in Sagittarius (WIYN, AURA, NSF, NOAO) M79 A globular cluster in Lepus (AURA, NSF, NOAO) M80 A globular cluster in Scorpius (F. R. Ferraro (ESO /Bologna Obs.), M. Shara (STSci /AMNH) et al., & the Hubble Heritage Team (AURA/ STScI/ NASA), apod990707) M92 A globular cluster in Hercules (Martin Germano; obtained from SEDS site) M107 A globular cluster in Ophiuchus (AURA, NSF, NOAO) The Messier Catalog: Open Star Clusters M6 -- The Butterfly Cluster An open cluster in Scorpius (AURA, NOAO, NSF, apod990106) M7 An open cluster in Scorpius (R. Barba, N. Morrell et al. (UNLP), CTIO, NOAO, NSF, apod020505) M11 An open cluster in Scutum (Jean-Charles Cuillandre (CFHT), Hawaiian Starlight, CFHT, apod0301220) M16 An open cluster in Serpens Cauda, associated with the Eagle Nebula (P. Challis (CfA), Whipple Obs., 1.2 m Telescope, apod970718) M18 An open cluster in Sagittarius (Hillary Mathis, REU program, AURA, NSF, NOAO) M21 An open cluster in Sagittarius (REU Program, AURA, NSF, NOAO) M23 An open cluster in Sagittarius (N. A. Sharp, REU Program, AURA, NSF, NOAO) M24 Star clouds in Sagittarius (Fred Calvert & Adam Block, NOAO, AURA, NSF, apod040921) M25 An open cluster in Sagittarius (Hillary Mathis, Vanessa Harvey, REU program, AURA, NSF, NOAO) M26 An open cluster in Scutum (Hillary Mathis, Vanessa Harvey, REU program, AURA, NSF, NOAO) M29 An open cluster in Cygnus (Hillary Mathis, AURA, NSF, NOAO) M34 An open cluster in Perseus (REU program, AURA, NSF, NOAO) M35 An open cluster in Gemini, approximately 3000 light years away M35 fills the left half of this image; the "small" cluster lower right is the larger, more distant NGC2158 (N. A. Sharp, NOAO, AURA, NSF, apod021129) M36 An open cluster in Auriga (AURA, NSF, NOAO) M37 An open cluster in Auriga (Martin Altmann, Fabian Heitsch, Oliver Cordes, Hoher List Observatory; obtained from SEDS site) M38 An open cluster in Auriga (NOAO, AURA, NSF, apod030107) M39 An open cluster in Cygnus (Heidi Schweiker, WIYN, NOAO, AURA, NSF, apod040331) M40 A double star in Ursa Major (AURA, NSF, NOAO) M41 An open cluster in Canis Major (AURA, NSF, NOAO) M44 -- Praesepe, the Beehive Cluster An open cluster in Cancer (Wil Milan, apod980803) M45 -- Subaru, the Pleiades, the Seven Sisters An open cluster in Taurus (Robert Gendler, apod031227) M46 An open cluster in Puppis (Wil Milan, apod990305) M47 An open cluster in Puppis (Original image by Chris Hetlage shows M46 and M47, apod050804) M48 An open cluster in Hydra (AURA, NSF, NOAO) M50 An open cluster in Monoceros (S. Kohle, T. Credner et al., apod970128) M52 An open cluster in Casseiopeia (AURA, NSF, NOAO) M67 An open cluster in Cancer (Nigel Sharp, Mark Hanna, AURA, NSF, NOAO) M73 An open cluster in Aquarius (REU program, AURA, NSF, NOAO) M93 An open cluster in Puppis (AURA, NSF, NOAO) M103 An open cluster in Casseiopeia (Hillary Mathis & N. A. Sharp, KPNO 2.1-m Tel., AURA, NOAO, NSF, apod010207) The Messier Catalog: Galaxies (Also see Charles Messier's Catalog: Nebulae / Open Clusters / Globular Clusters; The Andromeda Galaxy, M81 and M82: A Cosmic Train Wreck, Pictures of Other Galaxies) M31 -- The Andromeda Galaxy A spiral galaxy in Andromeda (Robert Gendler, apod051222) M32 An elliptical galaxy, a satellite of M31 (the small galaxy above M31) (Robert Gendler, apod051222) M33 -- The Triangulum Galaxy A spiral galaxy in Triangulum (Robert Gendler, apod041214) M49 An elliptical galaxy in Virgo (AURA, NSF, NOAO) M51 -- The Whirlpool Galaxy A spiral galaxy in Canes Venatici (S. Beckwith (STScI) Hubble Heritage Team, (STScI/AURA), ESA, NASA, apod061111) M58 A barred spiral galaxy in Virgo (Fred Cieslak, Adam Block, AURA, NSF, NOAO) M59 An elliptical galaxy in Virgo (AURA, NSF, NOAO) M60 An elliptical galaxy in Virgo (lower left), and a more distant spiral, NGC4647 (AURA, NSF, NOAO) M61 A barred spiral galaxy in Virgo (Adam Block, AURA, NSF, NOAO) M63 A spiral galaxy in Canes Venatici (Satoshi Miyazaki (NAOJ), Suprime-Cam, Subaru Telescope, NOAJ, apod000627) M64 A spiral galaxy in Coma Berenices (NASA and the Hubble Heritage Team (AURA/STScI), S. Smartt (IoA) & D. Richstone (U. Michigan) et al., apod040211) M65 A spiral galaxy in Leo (Chuck Greenberg, Scott Tucker, Adam Block, AURA, NSF, NOAO) M66 A spiral galaxy in Leo Only 35 million light years away, this hundred thousand light year wide spiral is a member of the well-studied Leo Triplet of galaxies. Gravitational interaction with other members of the small group has probably influenced the structure of its dustfilled arms, and the formation of clusters of bright young stars which light up those arms. (M. Neeser (Univ.-Sternwarte Munchen), P. Barthel (Kapteyn Astron. Institute), H. Heyer, H. Boffin (ESO), ESO, apod060902) M74 A spiral galaxy in Pisces (Gemini Observatory, GMOS Team, apod030524) M77 A spiral galaxy in Cetus, also known to be a Seyfert galaxy (Ken Crawford (Rancho Del Sol Observatory), apod061207) M81 A spiral galaxy in Ursa Major, orbiting around M82 M82 A spiral galaxy in Ursa Major, orbiting around M81 M83 A spiral galaxy in Hydra (FORS Team, 8.2-meter VLT Antu, ESO, apod030511) M84 A lenticular (S0) or elliptical galaxy in Virgo (AURA, NSF, NOAO) M85 A lenticular (S0) galaxy in Coma Berenices (AURA, NSF, NOAO) M86 A lenticular (S0) galaxy in Virgo (AURA, NSF, NOAO) M87 An elliptical galaxy in Virgo (Canada-France-Hawaii Telescope, J.-C. Cuillandre (CFHT), Coelum, apod040616) M88 A spiral galaxy in Coma Berenices (AURA, NSF, NOAO) M89 An elliptical galaxy in Virgo (AURA, NSF, NOAO) M90 A spiral galaxy in Virgo (Gary and Jeri Siegelman, Adam Block, AURA, NSF, NOAO) M91 A spiral galaxy in Coma Berenices (NOAO) M94 A spiral galaxy in Canes Venatici (Hillary Mathis & N.A.Sharp (NOAO), AURA, NSF, apod021121) M95 A spiral galaxy in Leo (AURA, NSF, NOAO) M96 A spiral galaxy in Leo (AURA, NSF, NOAO) M98 A spiral galaxy in Coma Berenices (Kitt Peak National Observatory, AURA, NSF, NOAO) M99 A spiral galaxy in Coma Berenices (N. A. Sharp, Kitt Peak National Observatory, AURA, NSF, NOAO) M100 A spiral galaxy in Coma Berenices (FORS Team, 8.2-meter VLT, ESO, apod060307) M101/M102 -- The Pinwheel Galaxy A spiral galaxy in Ursa Major (M102 was an inadvertent duplication, due to an erroneous communication) (NASA, ESA, CFHT, NOAO; Acknowledgement - K.Kuntz (GSFC), F.Bresolin (U.Hawaii), J.Trauger (JPL), J.Mould (NOAO), Y.-H.Chu (U. Illinois), apod060302) M104 -- The Sombrero Galaxy A spiral galaxy in Virgo (David Malin, Anglo-Australian University, apod990815) M105 An elliptical galaxy in Leo (AURA, NSF, NOAO) M106 A spiral galaxy in Canes Venatici (Bernie and Jay Slotnick, Adam Block, AOP, NOAO, AURA, NSF, apod030417) M108 A spiral galaxy in Ursa Major (AURA, NSF, NOAO) M109 A spiral galaxy in Ursa Major (AURA, NSF, NOAO) M110 A dwarf elliptical galaxy in Andromeda A satellite of M31, also known as NGC205, M110 is the elliptical galaxy below M31, in the image of that galaxy, above. About 15000 light-years across, M110 is comparable in size to the Magellanic Clouds, which are satellites of our galaxy. Elliptical galaxies usually contain little gas, and only old stars, but M110 has dust clouds, and young stars, perhaps as a result of its gravitational interaction with M31. (Robert Gendler, apod051222) The Andromeda Galaxy A large-scale image of M31, the Andromeda Galaxy, emphasizing the various colors of regions stars, by using different choices for the colors assigned to black-and-white images taken at various elliptical above M31 is M32, while the larger, more elongated elliptical below it is M110 (also ca Gendler, apod051222) M81 and M82: A Cosmic Train Wreck When I began teaching, in 1970, introductory discussions of galactic collisions usually suggested that stars in each of the colliding galaxies would pass undisturbed, right through the other galaxy, because the stars were so infinitely small in comparison to the vast distances between them, that collisions or even near-collisions of stars would be rare or nonexistent. We now know that this view is completely wrong; for even though stars might not directly collide with each other, each galaxy's gravity would so strongly affect the motion of stars in the other galaxy, that the colliding galaxies would tear each other to pieces, scattering stars in all directions in intergalactic space, only to fall back together, under the combined influence of their mutual gravity, to form a new galaxy. As dramatic as such a collision would be, it is as nothing compared to the most noticeable effect of galactic collisions. For galaxies contain not only stars, but also huge amounts of gas and dust, and as the galaxies near or pass through each other, the gases are violently compressed, causing extraordinary episodes of star formation known as starbursts. The heat and radiation emitted by the vast numbers of stars formed in such bursts energize the gas and dust left over from their formation, blowing them violently outward in a "superwind" of stupendous energy and magnitude. The images immediately below show a relatively minor example of the effects caused by the recent near passage of two nearby galaxies, M81 and M82. As you examine the images and read their captions, you will see that the violent events recorded by these images may be the latest, but are by no means the most important episode of stellar interactions between these two galaxies, and that their past and future contain cataclysmic events that dwarf by far their present activity. M81 (left) and M82 (right), two nearby (only 12 million light years from us) galaxies in Ursa Major. Each is visible as a faint smudge in a small telescope, the larger and brighter M81 of course a bit more noticeably. The two galaxies are orbiting each other about once every hundred million years, probably as a result of a near-collision about six hundred million years in the past; and each time they pass by each other, they undergo episodes of star formation caused by their gravitational interaction. M81's bright spiral arms are the site of star formation, partially caused by density waves raised by the most recent passage of M82, and the central portion of M82 is undergoing a starburst -- an explosively rapid surge of star formation and death -- which is violently blowing huge amounts of gas and dust out of the galaxy, causing the fuzzy blurring near its center, and emitting huge amounts of radiation, all the way from the infrared, to the X-ray region. Each hundred-million year passage will probably bring the two galaxies closer together. At first, this will probably produce more and more extreme waves of star formation; but within a few billion years, the two galaxies should tear each other to pieces, and after a period of considerable chaos, merge into a new, brighter and larger galaxy. As an aside, it is interesting to compare this image, in which H-alpha images which emphasize the emissions from hydrogen gas were combined with visible-light images, with a very similar (apod000209) image, which did not enhance the hydrogen emissions. As discussed in False Colors in Astronomical Photographs, the more interesting an image looks, the more work had to be done to make it look that way, and the less likely it is that it looks like "the real thing". (Johannes Schedler (Panther Observatory), apod060415) A closer look at M81 highlights the numerous hot, bright blue young stars which are lighting up the glowing clouds of hydrogen gas in its spiral arms. (Johannes Schedler (Panther Observatory), apod060415) A closer view of M82 (a photomosaic of Hubble Space Telescope images released to celebrate the sixteenth anniversary of the space observatory) highlights the red light strongly emitted by superheated hydrogen gas, driven out of the core of the galaxy by a "superwind" created by large numbers of young, massive stars formed by the galaxy's most recent interaction with M81. In this image, filaments of glowing gas extend for more than ten thousand light years. The hot gas emits so much infrared radiation that at long wavelengths, M82 is the brightest galaxy in the sky. (NASA, ESA, The Hubble Heritage Team, (STScI / AURA), M. Mountain (STScI), P. Puxley (NSF), J. Gallagher (U. Wisconsin), apod060425) Yet another image of M82, taken with the Hubble Space Telescope, concentrates more on the visible light of stars, and the dust obscuring that light, than on the infrared radiation of the heated gases sweeping away from the galaxy. Numerous globular clusters are revealed, which have a surprising property. Usually, globular clusters, such as those in our own galaxy, are ten to twelve billion years old, and date to the earliest days of galaxy formation; but studies of the cluster diagrams (Hertzsprung-Russell Diagrams of star clusters) for the globulars in M82 reveal that they are only 600 million years old (practically newborns, by stellar standards), as their hottest, brightest stars -- stars that are burning their fuel so quickly that they are nearly at the end of their Main Sequence lives -- are much brighter than the hottest, brightest stars in other globular clusters, and can't be much more than half a billion years old. The starburst that is ejecting huge amounts of heated gas and dust into intergalactic space is believed to have occurred as a result of the most recent passage of M81 by M82, sometime within the last hundred million years; but a far more more spectacular stage of star formation must have accompanied the formation of M82's young globulars, which may well have been caused by a nearcollision of the two galaxies a little over half a billion years ago; and even more spectacular events await the two galaxies when they tear each other apart and merge into a new galaxy, a few billion years from now. (Richard de Grijs (Cambridge IoA) et al., ESA, NASA, apod010312) Another view of M82, taken by the Spitzer Space Telescope, emphasizes the infrared radiation of the escaping gas and dust, and underplays the radiation from the stars within the body of the galaxy, which primarily emit visible light. Analysis of the wavelengths most strongly emitted by the gas shows that it contains large amounts of polycyclic aromatic hydrocarbons -- complex organic compounds frequently found in star-forming regions in our own galaxy -- which are almost literally cosmic smoke particles, as they are common products of combustion on Earth. (Considering that, on account of its visible-light shape, M82 is often referred to as the Cigar Galaxy, the presence of such noxious particles seems particularly appropriate.) The Spitzer image not only reveals the nature of the dust, but also shows that gas, smoke and dust extend even further than previously suspected -nearly twenty thousand light-years above and below the plane of the galaxy. (C. Engelbracht (Steward Obs.), et al. JPL, Caltech, NASA, apod060414) Pictures of Other Galaxies (Also see The Messier Catalog: Galaxies) M74, a spiral galaxy in Pisces. An Sc galaxy containing 100 billion stars, approximately 30 million light years away. Somewhat smaller than our own galaxy, but otherwise very similar in structure. (Gemini Observatory, GMOS Team, apod030524) Another Sc galaxy, in Sculptor, seen nearly from the side. NGC253 is about 10 million light years away, in the Sculptor Group of galaxies, the nearest group to our own Local Group of galaxies. (Jean-Charles Cuillandre (CFHT), Hawaiian Starlight, CFHT, apod030525) A "thin" spiral galaxy, NGC 5866, is seen exactly edge-on, so that the lanes of gas and dust that fill its disk appear to be nearly a straight line. As remarkable as the galaxy appears, it is likely that many spiral galaxies would appear equally thin if seen from such an angle. The blue disk of young stars extends well past the thin dust lanes, while the central bulge, more orange in color, due to the older, redder stars that exist in the nucleus, extends above and below the disk. About 60 thousand light years in diameter, and 45 million light years away, in the constellation of Draco the Dragon, NGC 5866 is about 30% smaller than our galaxy, but about equally massive, based on its rotational rate. (NASA, ESA, and The Hubble Heritage Team (STScI/AURA), W. Keel (U. Alabama), apod060612) (AURA, NSF, NOAO) Galaxies are always much bigger than they appear in "normally" exposed photographs. Above and below are images of M77, a spiral galaxy in Cetus. The image above (rotated 45 degrees, to correspond to the orientation of the image below; the white lines show the edge of the original image) shows the galaxy as usually photographed, with an unusually bright core (hence its designation as a Seyfert galaxy), and tightly wound spiral arms extending a moderate distance from the core. The image below, which uses a much longer exposure for the outer regions, shows that the actual structure is many times larger. Although the density of stars per unit of space is lower in the outer, fainter parts of galaxies, the much larger extent of those regions makes the overall mass of the outer regions comparable to, or even larger than, the mass of the "visible" portions of the galaxy. (Ken Crawford (Rancho Del Sol Observatory), apod061207) M83, a barred spiral galaxy in Hydra. One of the closest galaxies, at only 15 million light years distance. (FORS Team, 8.2meter VLT, ESO, apod030511) NGC 1365, a barred spiral galaxy in the Fornax Cluster. A rotating density wave helps maintain the structure of the bar and promotes the creation of new stars, which light up the spiral arms extending from the bar. (FORS Team, 8.2-meter VLT Antu, ESO, apod030413) Bright blue giants light up the outer arms of the strikingly barred spiral galaxy NGC 1300. The 100,000 light-year-diameter galaxy lies a mere 70 million light years away, allowing a detailed examination of its structure, including the remarkable spiral structure near its center. (Hubble Heritage Team, ESA, NASA, apod060827) ESO 510-13, a warped spiral galaxy, seen from the side. About 100,000 light years across, and 150 million light years away. From this direction, dust in the disk obscures the view. (Hubble Heritage Team (STScI / AURA), C. Conselice (U. Wisconsin / STScI) et al., NASA, apod030607) M106, a spiral galaxy in Canes Venatici. A relatively small galaxy, at only 30,000 light years across, but only 21 million light years away. Notable because it is a Seyfert galaxy, having an exceptionally bright core. (Bernie and Jay Slotnick, Adam Block, AOP, NOAO, AURA, NSF, apod030417) A galactic collision in the Perseus Cluster, about 230 million light years away. Two galaxies, a dusty spiral near the center, and an elliptical at lower left, are colliding. Each galaxy, about 50,000 light years across, is distorted by the gravity of the other one, and as clouds of gas in the galaxies collide, bursts of star formation occur. See M81 and M82: A Cosmic Train Wreck for more about galactic collisions. (Hubble Heritage Team (STScI/AURA), M. Donahue (STScI) & J. Trauger (JPL), NASA, apod030505) A face-on spiral galaxy in Centaurus. ESO269-57 (the -57 refers to its declination) is a relatively large galaxy, almost 200,000 light years across. Its distance of 150 million light years means that we see it as it was 150 million years ago. (FORS1, VLT, ESO, apod030419) A type II supernova, as observed in 1999, in a galaxy in Ursa Major. The bright dot just above the center of the galaxy, NGC 3184, is the supernova. (This is NOT the bright dot near the top of the galaxy, which is a nearby star, in our own galaxy.) NGC 3814 is a type Sbc galaxy about 50,000 light years across, or about half the size of our galaxy. (Al Kelly (JSCAS/NASA) & Arne Henden (Flagstaff/USNO), apod000920)