Download A Comet-Hunter`s Legacy -

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)