Leviathan's Deep Sky Object of the Week #11:
The Southern Pinwheel Galaxy - Messier 83
Constellation: Hydra
Right ascension: 13h 37m 00.9s
Declination: -29° 51′ 57″
Redshift: 513 ± 2 km/s
Distance: 14.7 Mly (4.5 Mpc)
Type: SAB(s)
Apparent dimensions(V): 12′.9 × 11′.5
Apparent magnitude (V): 7.54
Right ascension: 13h 37m 00.9s
Declination: -29° 51′ 57″
Redshift: 513 ± 2 km/s
Distance: 14.7 Mly (4.5 Mpc)
Type: SAB(s)
Apparent dimensions(V): 12′.9 × 11′.5
Apparent magnitude (V): 7.54
This spectacular spiral galaxy is known to astronomers as Messier 83. Colloquially, it is also called the Southern Pinwheel due to its similarity to the more northerly Pinwheel galaxy Messier 101. M83 is classified as a starburst galaxy - a galaxy where a great deal of star formation is taking place. The image above shows us, in spectacular detail, the numerous star clouds full of bright young blue giant stars whose births may have been triggered by massive gravitational interactions between M83 and one of several nearby companion galaxies. In the image above we can also see a fantastic amount of gas and dust structure in what many people think of as our own Milky Way galaxy's smaller cousin.
Living in the middle of the Milky Way's disk, we see our galaxy only from an obstructed vantage point that is both inside-out and edge-on. We see Messier 83 nearly face-on, giving us a chance to really map out its disk in great detail. This information helps astronomers figure out what our own galaxy would look like if we could warp out to a better vantage point.
Like the Milky Way, Messier 83 is classified as a barred spiral galaxy due to the bar-like pattern of stars that run through its center. This bar region is more interesting in the infrared (see below) since we can also see the open s shaped curve of dust (red) cutting through the more linear stellar bar (blue-cyan).
Living in the middle of the Milky Way's disk, we see our galaxy only from an obstructed vantage point that is both inside-out and edge-on. We see Messier 83 nearly face-on, giving us a chance to really map out its disk in great detail. This information helps astronomers figure out what our own galaxy would look like if we could warp out to a better vantage point.
Like the Milky Way, Messier 83 is classified as a barred spiral galaxy due to the bar-like pattern of stars that run through its center. This bar region is more interesting in the infrared (see below) since we can also see the open s shaped curve of dust (red) cutting through the more linear stellar bar (blue-cyan).
Spitzer Space Telescope infrared image of the beautiful and complex tangles of cooler dust and gas clouds hidden within the arms of the spiral galaxy.
This arc of inner dust connects up with the more tightly wound spiral arms in the outer disk, seen here as bright green-red ridges. Between the main spiral arms we also see a complex webbing of dust that permeates the entire disk.
Another interesting note is that, just one year ago, the Chandra X-ray Satellite detected an ultra-luminous x-ray source (ULX) near the supermassive black hole at the center of the galaxy. For several short periods of time, over the last year, this source has brightened the total X-ray output of the black hole region by over 3000x! Astronomers now interpret these flucuations as episodes where the accrection disk around the supermassive black hole is being impacted by gases being ripped from the outer layers of a red giant star orbiting near the accretion disk's edge. So we have actual evidence of a star being eaten by a supermassive black hole. (A similar situation occured in the Andromeda galaxy (M31) just recently).
In 2006, astronomers using a high resolution infrared spectrometer on the Gemini South telescope detected a "high mass concentration" hidden in one side of the bar near the center of the galaxy. Models suggest that this could be a second nucleus from a smaller galaxy that has been swallowed up and incorporated into the larger barred spiral. The nucleus of the intruder body has an estimated mass of about 16 million times the mass of the Sun, compared to 2 million solar masses for the optical "main" nucleus. The two nuclei are about 100 parsecs apart and are probably harboring black holes. Numerical modeling conducted by the team suggest that the two nuclei would coalesce to form a single massive core in about 60 million years.
Another interesting note is that, just one year ago, the Chandra X-ray Satellite detected an ultra-luminous x-ray source (ULX) near the supermassive black hole at the center of the galaxy. For several short periods of time, over the last year, this source has brightened the total X-ray output of the black hole region by over 3000x! Astronomers now interpret these flucuations as episodes where the accrection disk around the supermassive black hole is being impacted by gases being ripped from the outer layers of a red giant star orbiting near the accretion disk's edge. So we have actual evidence of a star being eaten by a supermassive black hole. (A similar situation occured in the Andromeda galaxy (M31) just recently).
In 2006, astronomers using a high resolution infrared spectrometer on the Gemini South telescope detected a "high mass concentration" hidden in one side of the bar near the center of the galaxy. Models suggest that this could be a second nucleus from a smaller galaxy that has been swallowed up and incorporated into the larger barred spiral. The nucleus of the intruder body has an estimated mass of about 16 million times the mass of the Sun, compared to 2 million solar masses for the optical "main" nucleus. The two nuclei are about 100 parsecs apart and are probably harboring black holes. Numerical modeling conducted by the team suggest that the two nuclei would coalesce to form a single massive core in about 60 million years.
M83 sketched through an 6" f8 Newtonian telescope at 220x from suburban skies. Image by János Gábor Kernya.
While Messier 83 is about 15 million light years away, it is actually one of the closest barred spiral galaxies in the sky. This gives astronomers an excellent chance to study a galaxy that, although half as big, seems very similar in structure to our own Milky Way galaxy.
Finder chart for M83 galaxy - it is low from mid-northern latitudes, so you'll need to probably wait for the galaxy to transit due south for it to reach a more favourable elevation. (A low horizon of trees and buildings to the south is also recommended). Click to enlarge.
Here are some observation notes I made while observing this galaxy from a dark sky location along the north shore of lake Erie with my 8" f 6.7 newtonian telescope on a moonless night many years ago using a magnification of 175x:
"Wow, what a beautiful spiral galaxy! It is very bright, large, and elongated, with two fairly tightly wound spiral arms - one of which has a more severe bend in it than the other. The core of the galaxy is quite bright and a few dusty wisps of hazy light can be barely perceived in the arms (dust lanes?). Averting my eye towards the side of the field of view through the eyepiece really helps improve the brightness and detail visible in the arms. After locating it and checking its position over the barrel of the telescope, it has become pretty easy to spot in the finderscope. A third arm appears to be jutting out of the less severely curved are about 1/3 -1/2 of the way around it from the center."
In a 20" f/4 dobsonian, using a 13mm Nagler and Parracor, Steven Coe reports, "spiral arms obvious, core blazing with 3 to 4 arc sec in size, many bright areas in arms (probably giant star clusters or HII regions).
Steven also reports that when viewed from the Texas Star Party through a 36" f/5 with a 20mm Nagler eyepiece, the "spiral was easy; averted vision makes the spiral structure more obvious and increases size 30%. Many small knots in the arms. Amazing amount of detail. Core a very light yellow."
"Wow, what a beautiful spiral galaxy! It is very bright, large, and elongated, with two fairly tightly wound spiral arms - one of which has a more severe bend in it than the other. The core of the galaxy is quite bright and a few dusty wisps of hazy light can be barely perceived in the arms (dust lanes?). Averting my eye towards the side of the field of view through the eyepiece really helps improve the brightness and detail visible in the arms. After locating it and checking its position over the barrel of the telescope, it has become pretty easy to spot in the finderscope. A third arm appears to be jutting out of the less severely curved are about 1/3 -1/2 of the way around it from the center."
In a 20" f/4 dobsonian, using a 13mm Nagler and Parracor, Steven Coe reports, "spiral arms obvious, core blazing with 3 to 4 arc sec in size, many bright areas in arms (probably giant star clusters or HII regions).
Steven also reports that when viewed from the Texas Star Party through a 36" f/5 with a 20mm Nagler eyepiece, the "spiral was easy; averted vision makes the spiral structure more obvious and increases size 30%. Many small knots in the arms. Amazing amount of detail. Core a very light yellow."
The Dumbbell Nebula can be found about 1/3 of the way up from the tip of the Arrow constellation (Sagitta) to the nose of the constellation Cygnus (the swan).
Leviathan's Deep Sky Object of the Week #11: Edge-On Spiral Galaxy
The Whale Galaxy
Other designations: Whale Galaxy, UGC 7865, PGC 42637, Arp 281,
Caldwell 32
Constellation: Canes Venatici
Right ascension: 12h 42m 08.0s
Declination:+32° 32′ 29″
Redshift: 606 ± 3 km/s
Distance: 27 +/- 3.1 Mly
Type: SB(s)d
Apparent dimensions: (V) 15′.5 × 2′.7
Apparent magnitude: (V) +9.8
Caldwell 32
Constellation: Canes Venatici
Right ascension: 12h 42m 08.0s
Declination:+32° 32′ 29″
Redshift: 606 ± 3 km/s
Distance: 27 +/- 3.1 Mly
Type: SB(s)d
Apparent dimensions: (V) 15′.5 × 2′.7
Apparent magnitude: (V) +9.8
NGC 4361, also known as the Whale Galaxy for its obvious resemblance to the silhouette of large baleen cetaceans, is bright enough to be seen in binoculars from darker locations. Image by Diane Zeiders and Adam Block through a 20" telescope (KPO).
NGC 4631 is a magnitude 9.8 edge-on spiral galaxy in Canes Venatici. The lens or disk shape of this galaxy is distorted with a thicker wedge at one end. In photos and visual observations with medium- to large-size telescopes, it resembles the view of a blue whale and is therefore known as “the Whale galaxy.” The galaxy is approximately thirty million light years away and is part of the NGC 4631 galaxy group. Its closest companion is magnitude 13.1 galaxy NGC 4627, an elliptical dwarf also known as “The Calf.” Together, they are known popularly as “The Whale and Calf.”
NGC 4631 contains a central starburst region, which is an area of intense star formation. The strong star formation is evident in the emission from ionized hydrogen and interstellar dust heated by the stars formed in the starburst. The most massive stars that form in star formation regions only burn hydrogen gas through fusion for a short period of time, after which they explode as supernovae. So many supernovae have exploded in the center of NGC 4631 that they are blowing gas out of the plane of the galaxy. This superwind can be seen in X-rays and in spectral line emission. The gas from this superwind has produced a giant, diffuse corona of hot, X-ray emitting gas around the whole galaxy. (Click on the image below for a closer view of this activity by the Hubble Space Telescope.)
Here, a profusion of starbirth lights up the galactic centre, revealing bands of dark material between us and the starburst. The galaxy’s activity tapers off in its outer regions where there are fewer stars and less dust, but these are still punctuated by pockets of star formation. Image by the Hubble Space Telescope Science Institute.
NGC 4631 has a nearby companion dwarf elliptical galaxy, NGC 4627. NGC 4627 and NGC 4631 together were listed in the Atlas of Peculiar Galaxies as an example of a "double galaxy" or a galaxy pair.
NGC 4631 and NGC 4627 are part of the NGC 4631 Group, a group of galaxies that also includes the interacting galaxies NGC 4656 and NGC 4657 (which together are also known as the 'Hockey Stick' galaxy. However, exact group identification is problematic because this galaxy and others lie in a part of the sky that is relatively crowded. Estimates of the number of galaxies in this group range from 5 to 27, and all studies identify very different member galaxies for this group.
NGC 4631 and NGC 4627 are part of the NGC 4631 Group, a group of galaxies that also includes the interacting galaxies NGC 4656 and NGC 4657 (which together are also known as the 'Hockey Stick' galaxy. However, exact group identification is problematic because this galaxy and others lie in a part of the sky that is relatively crowded. Estimates of the number of galaxies in this group range from 5 to 27, and all studies identify very different member galaxies for this group.
Observer's Notes:
As mentioned above, a large number of stars in the central core have apparently exploded as supernovae in a short time frame and they are ejecting massive amounts of gas from the core, creating a superwind. Unfortunately, this wind can only be seen in X-ray photos. For visual observing, there is no indication this is happening. However, what is noticeable, at high power in telescopes with apertures of 8 inches or larger, is small tufts and wisps of nebulosity extending irregularly and mostly perpendicular to the spiral's dust lane. The dust lane itself is differentiated and mottled in its appearance - sometimes darker and thinner near one end and then fainter and broken towards the other. Small bright patches pop in and out on either side of the central axis -these are giant star burst regions within the galaxy - clouds filled with newly formed bright blue giant stars. On crisp nights of good seeing, the detail that can be seen at higher powers is significant, particularly with apertures larger that 14 inches.
As mentioned above, a large number of stars in the central core have apparently exploded as supernovae in a short time frame and they are ejecting massive amounts of gas from the core, creating a superwind. Unfortunately, this wind can only be seen in X-ray photos. For visual observing, there is no indication this is happening. However, what is noticeable, at high power in telescopes with apertures of 8 inches or larger, is small tufts and wisps of nebulosity extending irregularly and mostly perpendicular to the spiral's dust lane. The dust lane itself is differentiated and mottled in its appearance - sometimes darker and thinner near one end and then fainter and broken towards the other. Small bright patches pop in and out on either side of the central axis -these are giant star burst regions within the galaxy - clouds filled with newly formed bright blue giant stars. On crisp nights of good seeing, the detail that can be seen at higher powers is significant, particularly with apertures larger that 14 inches.
Sketch by Roel Weljenberg, 300mm f/4 dobsonian truss telescope, Deventer, The Netherlands
Smaller telescopes show some features as well. In a 4 inch refractor at Starfest a few years ago, I recorded a few notes on my observation of this galaxy:
" Saw the Whale as a ghostly streak of light, almost like a short smoke trail of a passing shooting star. The galaxy's edges in places are so soft and subtle that its boundaries are difficult to determine. The galaxy’s core looks a tad brighter and elongated in an E-W direction as well. The dusty dark lane edge of the galaxy's arms is more distinct and obvious from the midpoint to the western edge. It definitely has a mottled appearance at high power. Also, a faint star (mag. 12) is noticeable near the northern edge of the galaxy’s glow."
Although not technically part of the this week's visual challenge, it is hard to view just the Whale and Calf without seeing NGC 4656/4657, the “Hockey Stick”, in the same field of view. Using a wide-field eyepiece, both pairs of galaxies can be squeezed into the field. NGC 4656 is another edge-on galaxy that has a companion. This companion, NGC 4657, interacts with NGC 4656 and distorts one end of the streak, giving observers the real impression of a hockey stick. They were discovered by William Herschel in 1787. This magnitude 10.4 galaxy and its companion is a nice addition to the observing experience.
Click on the finder chart below to help you locate this galaxy grouping among the constellations of the spring sky.
" Saw the Whale as a ghostly streak of light, almost like a short smoke trail of a passing shooting star. The galaxy's edges in places are so soft and subtle that its boundaries are difficult to determine. The galaxy’s core looks a tad brighter and elongated in an E-W direction as well. The dusty dark lane edge of the galaxy's arms is more distinct and obvious from the midpoint to the western edge. It definitely has a mottled appearance at high power. Also, a faint star (mag. 12) is noticeable near the northern edge of the galaxy’s glow."
Although not technically part of the this week's visual challenge, it is hard to view just the Whale and Calf without seeing NGC 4656/4657, the “Hockey Stick”, in the same field of view. Using a wide-field eyepiece, both pairs of galaxies can be squeezed into the field. NGC 4656 is another edge-on galaxy that has a companion. This companion, NGC 4657, interacts with NGC 4656 and distorts one end of the streak, giving observers the real impression of a hockey stick. They were discovered by William Herschel in 1787. This magnitude 10.4 galaxy and its companion is a nice addition to the observing experience.
Click on the finder chart below to help you locate this galaxy grouping among the constellations of the spring sky.
The Whale galaxy group can be almost exactly half-way along a straight line drawn from the tail star of the constellation Leo (named Denebola) to the star at the end of the handle of the Big Dipper (Aldaid). (Click on picture to enlarge).
Leviathan's Deep Sky Object of the Week Archive:
Leviathan's Deep Sky Object of the Week #9:
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Planetary NGC 2438
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Views through different optical aids:
M46
With a magnitude of 6.1, M46 is on the fringe of naked eye visibility. When
viewed through 10x50 binoculars, it appears of mottled appearance, more like a nebula than an open cluster. Also visible in the same field of view is the much brighter, similar sized but less rich cluster M47. About 0.5 degrees to the north of M47 is another open cluster NGC 2423 (7th magnitude). In 20x80 binoculars, the view of M46 is enhanced. The cluster appears large and dense with at least 50 faint members visible. Small telescopes show M46 as a sprinkling of stardust. A 80mm (3.1-inch) scope at high powers reveals many fainter stars of remarkably uniform brightness, especially when using averted vision.
M46 is a superb sight through a 200mm (8-inch) telescope, with dozens of white, blue-white stars visible. At a magnification of about 100x, the field of
view is completely filled with stars. In total, there are up to 150 stars brighter than magnitude 13 with the brightest stars being of magnitude 9. It is believed that there are at least 250 stars that are members of M46.
One notable feature of M46 is a planetary nebula (NGC 2438) located at the northern edge of the cluster. It is visible in small telescopes of the order of 100mm (4-inch). The nebula appears as a diffuse circular patch that seems to be a part of the open cluster, but is believed to be unrelated and purely a line of site phenomena.
M46
With a magnitude of 6.1, M46 is on the fringe of naked eye visibility. When
viewed through 10x50 binoculars, it appears of mottled appearance, more like a nebula than an open cluster. Also visible in the same field of view is the much brighter, similar sized but less rich cluster M47. About 0.5 degrees to the north of M47 is another open cluster NGC 2423 (7th magnitude). In 20x80 binoculars, the view of M46 is enhanced. The cluster appears large and dense with at least 50 faint members visible. Small telescopes show M46 as a sprinkling of stardust. A 80mm (3.1-inch) scope at high powers reveals many fainter stars of remarkably uniform brightness, especially when using averted vision.
M46 is a superb sight through a 200mm (8-inch) telescope, with dozens of white, blue-white stars visible. At a magnification of about 100x, the field of
view is completely filled with stars. In total, there are up to 150 stars brighter than magnitude 13 with the brightest stars being of magnitude 9. It is believed that there are at least 250 stars that are members of M46.
One notable feature of M46 is a planetary nebula (NGC 2438) located at the northern edge of the cluster. It is visible in small telescopes of the order of 100mm (4-inch). The nebula appears as a diffuse circular patch that seems to be a part of the open cluster, but is believed to be unrelated and purely a line of site phenomena.
M47
M47 appears as small fuzzy patch to the naked eye with the brightest stars just about resolvable under dark skies. With 10x50 binoculars it is an easy object. There are about 10-15 stars visible including at least half a dozen bright stars, spread over a diameter of 30 arc minutes. Larger 20x80 binoculars or small telescopes reveal a myriad of fainter stars of varying magnitudes, interspersed between the brighter members of this loose cluster. Also visible in the same wide field of view is M46 and another open cluster NGC 2423 (7th magnitude), which is located only 0.5 degrees to the northeast of M47. In stark contrast to M47, M46 is a denser but fainter and wider cluster with many more stars visible with a telescope. The two clusters together in a wide field telescope or binoculars offer one of the prettiest sights in the winter sky.
A 150mm (6-inch) telescope at low magnifications reveals M47 as a large loose cluster, with at least 10 or so brighter members and a few dozen fainter stars interspersed around them. A very close double star of equal magnitude components lies near the center of the cluster (Sigma 1121). These stars are of magnitude 7.9 and separated by 7.4 arc seconds. In total, M47 contains about 50 stars.
M47 appears as small fuzzy patch to the naked eye with the brightest stars just about resolvable under dark skies. With 10x50 binoculars it is an easy object. There are about 10-15 stars visible including at least half a dozen bright stars, spread over a diameter of 30 arc minutes. Larger 20x80 binoculars or small telescopes reveal a myriad of fainter stars of varying magnitudes, interspersed between the brighter members of this loose cluster. Also visible in the same wide field of view is M46 and another open cluster NGC 2423 (7th magnitude), which is located only 0.5 degrees to the northeast of M47. In stark contrast to M47, M46 is a denser but fainter and wider cluster with many more stars visible with a telescope. The two clusters together in a wide field telescope or binoculars offer one of the prettiest sights in the winter sky.
A 150mm (6-inch) telescope at low magnifications reveals M47 as a large loose cluster, with at least 10 or so brighter members and a few dozen fainter stars interspersed around them. A very close double star of equal magnitude components lies near the center of the cluster (Sigma 1121). These stars are of magnitude 7.9 and separated by 7.4 arc seconds. In total, M47 contains about 50 stars.
A deep exposure closeup of cluster M47
Check my Observer's Resources Page for more detailed finder charts for M46 and M47
Leviathan's Deep Sky Object of the Week: #7 NGC 1788
Alternative Designations: VdB or the Fox Face Nebula
Object Type: Reflection Nebula/ Molecular Cloud
Constellation: Orion
Right Ascension: 05h 06m 54s
Declination: -03° 21′ 00″ (deg:m:s)
Distance: 1300 ly
Visual Brightness: 9.0
Apparent Dimension: 8' x 8' of arc
Object Type: Reflection Nebula/ Molecular Cloud
Constellation: Orion
Right Ascension: 05h 06m 54s
Declination: -03° 21′ 00″ (deg:m:s)
Distance: 1300 ly
Visual Brightness: 9.0
Apparent Dimension: 8' x 8' of arc
_ The delicate nebula NGC 1788, located in a dark and often neglected corner of the constellation Orion, is revealed in this finely detailed image. NGC 1788 is a reflection nebula/molecular cloud in the process of birthing a new generation of stars hidden within its streamers of dust and gas. It is rather sharply defined on its southwest perimeter where it is flanked by the dark nebula known as Lynds 1616. Lynds 1616 is apparently part of NGC 1788. The brightest involved star is 10th magnitude and lies in the northwest sector. The brighter stars in this picture outside of the nebulosity are not a part of the cloud, but rather mostly foreground objects.
Click on the chart below to see a larger finder map of the object._
Click on the chart below to see a larger finder map of the object._
Leviathan's Deep Sky Object of the Week #5: M95 (with supernova!)
Alternative Designations: NGC 3351, UGC 5850
Object Type: Barred Spiral Galaxy ( Type SB(r)b )
Constellation: Leo
Right Ascension: 10h 43m 57.7s
Declination: +11° 42′ 14″ (deg:m:s)
Distance: 35.5 ± 1.4 Mly
Visual Brightness: 9.7
Apparent Dimension: 4.4' x 3.3' of arc
Object Type: Barred Spiral Galaxy ( Type SB(r)b )
Constellation: Leo
Right Ascension: 10h 43m 57.7s
Declination: +11° 42′ 14″ (deg:m:s)
Distance: 35.5 ± 1.4 Mly
Visual Brightness: 9.7
Apparent Dimension: 4.4' x 3.3' of arc
Messier 95 is a barred spiral galaxy 38 million light years away in the constellation Leo. The galaxy stands boldly face-on, offering an ideal view of its spiral structure. The spiral arms form an almost perfect circle around the galactic center before they spread out, creating a mane-like effect of which any lion would be proud. The diameter of M95 is about 75,000 light years (along its long axis), making it somewhat smaller than our own galaxy. Another, perhaps even more striking, feature of Messier 95 is its blazing golden core. It contains a nuclear star-forming ring, almost 2000 light-years across, where a large proportion of the galaxy’s star formation takes place. This phenomenon occurs mostly in barred spiral galaxies such as Messier 95 and our home, the Milky Way.
Pierre Méchain discovered M95, together with M96, March 20, 1781. Four days later, perhaps with some guidance from Méchain, Charles Messier observed it and included it in his catalog.
M95 was one of the galaxies in the key project of the Hubble Space Telescope for the determination of the Hubble constant: the HST was employed to look for Cepheid variable stars and thereby determine this galaxy's distance. It is now estimated to be 35.5 Mly distant from earth.
M95 was one of the galaxies in the key project of the Hubble Space Telescope for the determination of the Hubble constant: the HST was employed to look for Cepheid variable stars and thereby determine this galaxy's distance. It is now estimated to be 35.5 Mly distant from earth.
Messier 95 is a member of the Messier 96 Group of galaxies. This group also includes galaxies Messier 105, NGC 3373 and NGC 3384. A supernova was discovered in the galaxy's outskirts on March 16, 2012.
Despite its great distance, astronomers may have found the pre-nova star in a Hubble image that was made a few years ago. Here is an image of M95 that was made just after the supernova's appearance. Compare it with the image above to see if you can find the "new star" in the outer spiral arm at the bottom of the picture.
Despite its great distance, astronomers may have found the pre-nova star in a Hubble image that was made a few years ago. Here is an image of M95 that was made just after the supernova's appearance. Compare it with the image above to see if you can find the "new star" in the outer spiral arm at the bottom of the picture.
Locating Messier 95: M95 is the southernmost in the widefield eyepiece pairing of galaxies which includes M96. With good sky conditons, both M95 and M96 are easy to locate in the belly of the constellation of Leo. Begin by identifying Alpha (Regulus), the brightest, southernmost star in the backwards question mark asterism. Now, look about a fistwidth west where you will see the shallow triangle asterism which marks Leo’s hips. The westernmost of these stars (Theta) is your next marker. Look between the two markers for a faint star in an almost central position. If the skies are right to see this galactic pair, you will also see another star just south of your last marker. M95 and M96 are between these last two stars. The pair can just barely be seen in larger binoculars and although they are faint, perceivable in a small telescope. Larger aperture will bring out far more details. Because these are fainter galaxies, the require a dark sky location and cannot tolerate background glow, such as moonlit nights.
Leviathan's Deep Sky Object of the Week #2: The Snake Nebula
Alternate Designations: Barnard 72, LDN 113
Type: Dark Nebula
Right ascension 17h 23m 30s
Declination −23° 38′
Distance (ly) 650
Apparent magnitude (V) –
Apparent dimensions (V) 37 × 17 arcmins
Actual length of tube 3 - 4 lyrs
Constellation Ophiuchus
Type: Dark Nebula
Right ascension 17h 23m 30s
Declination −23° 38′
Distance (ly) 650
Apparent magnitude (V) –
Apparent dimensions (V) 37 × 17 arcmins
Actual length of tube 3 - 4 lyrs
Constellation Ophiuchus
The Snake Nebula is a series of dark absorption clouds made up of molecular gas and interstellar dust. Interstellar dust grains - composed predominantly of carbon - absorb visible starlight and reradiate much of it in the infrared. This absorption causes stars behind the clouds to be obscured from view, hence the appearance of starless voids on the sky. Molecular clouds like the Snake Nebula are places where new stars are likely to form.
The Snake Nebula is also known as Barnard 72. It is called a "dark nebula" by amateur astronomers. Dark nebulae don't have visual magnitudes listed because they are usually only detected as starless black forms silhouetted against the backdrop of the myriad of faint stars in the Milky Way. Barnard 72 has an opacity rating of 6 by the Deep Sky Field Guide, which is the maximum rating given to dark nebulae. B72 lies only about 1/2 degree south of where the ecliptic goes through Ophiuchus. If this cloud of gas was located sufficiently close to a star so the cloud of gas received strong ultraviolet radiation from the nearby star, the nebula would glow red
as an emission nebula.
The snake nebula is difficult to spot without dark sky conditions. A moonless sky is required and a dark observing location outside of the city is also essential. When searching for any dark nebula, remember that they are subtle creatures. It is not so much that you are looking for a dark sinuous cloud, but rather the absence of starlight or skyglow. Below is a star chart that you can enlarge by clicking on it. Good hunting!
The Snake Nebula is also known as Barnard 72. It is called a "dark nebula" by amateur astronomers. Dark nebulae don't have visual magnitudes listed because they are usually only detected as starless black forms silhouetted against the backdrop of the myriad of faint stars in the Milky Way. Barnard 72 has an opacity rating of 6 by the Deep Sky Field Guide, which is the maximum rating given to dark nebulae. B72 lies only about 1/2 degree south of where the ecliptic goes through Ophiuchus. If this cloud of gas was located sufficiently close to a star so the cloud of gas received strong ultraviolet radiation from the nearby star, the nebula would glow red
as an emission nebula.
The snake nebula is difficult to spot without dark sky conditions. A moonless sky is required and a dark observing location outside of the city is also essential. When searching for any dark nebula, remember that they are subtle creatures. It is not so much that you are looking for a dark sinuous cloud, but rather the absence of starlight or skyglow. Below is a star chart that you can enlarge by clicking on it. Good hunting!
Snake Nebula finder chart
Leviathan's Deep Sky Object of the Week #10: Planetary Nebula -
The Ghost of Jupiter
Alternative Designations: NGC 3242, Jupiter's Ghost, Eye Nebula,
Caldwell 59
Object Type: Planetary Nebula
Constellation: Hydra
Right ascension: 10h 24m
Declination: -18° 38′
Distance: 1400 ly
Apparent magnitude (V) 8.60
Apparent dimensions (V) 25″
Caldwell 59
Object Type: Planetary Nebula
Constellation: Hydra
Right ascension: 10h 24m
Declination: -18° 38′
Distance: 1400 ly
Apparent magnitude (V) 8.60
Apparent dimensions (V) 25″
Click to Enlarge.
As we (hopefully) start moving into warmer weather, we begin to see in the east the rise of the spring constellations with the setting of the Sun. Along with easily visible constellations of Cancer and Leo, we can also see the long constellation Hydra, climbing higher in the darkening sky just below them. Within the water serpent's boundaries is one of the less well-known
showpiece objects of the night sky. NGC 3242, also known as the 'Ghost of Jupiter', is a rather large and bright planetary nebula - basically a dying sun gently blowing its outer layers into interstellar space.
The talented English astronomer William Herschel, who discovered this nebula in 1785, noted its resemblance in size and shape to the planet Jupiter. But if you look at it carefully, you’ll find it takes on many other shapes and patterns, including that of a logo well known to TV viewers...the CBS "eye"! Like many such nebulae, NGC 3242 initially fooled some early observers who thought it looked in passing like the disk of a planet. Upon his discovery of this nebula, Herschel wrote, “Beautiful, brilliant, planetary disk ill defined, but uniformly bright, the light of the colour Jupiter… 1′ in diameter”.
A century later, the diligent amateur Admiral William Smyth wrote, “From
its size, equable light, and colour, this fine object resembles Jupiter.”
But it may have been Robert Burnham who first referred to this nebula as the “Ghost of Jupiter”. Though to many, the greenish hue of the nebula, caused by raving-hot oxygen atoms set aglow by the dying star, makes the nebula look more like Uranus than Jupiter. See for yourself… it’s a lovely sight and well worth close inspection on an early spring night.
The nebula lies about 1,600 light years away, and spans 0.5 light years. The central star of the nebula shines at a dim magnitude 12.5. Its central core glows at 90,000 Kelvin; it will soon settle down as a slowly-cooling white dwarf.
The “Ghost of Jupiter” deserves at least as much attention as the more famous Ring Nebula in the constellation Lyra. Like the Ring Nebula, NGC 3242 is also a planetary nebula, the last hurrah of a star that’s run out of fuel and approaches the end of its life as a white dwarf. But at a relatively bright magnitude 7.3, NGC 3242 is at least 2 magnitudes brighter than the Ring Nebula, and not much harder to find. Look for it about 2 degrees southwest of the star μ (mu) Hydrae (see map below).
showpiece objects of the night sky. NGC 3242, also known as the 'Ghost of Jupiter', is a rather large and bright planetary nebula - basically a dying sun gently blowing its outer layers into interstellar space.
The talented English astronomer William Herschel, who discovered this nebula in 1785, noted its resemblance in size and shape to the planet Jupiter. But if you look at it carefully, you’ll find it takes on many other shapes and patterns, including that of a logo well known to TV viewers...the CBS "eye"! Like many such nebulae, NGC 3242 initially fooled some early observers who thought it looked in passing like the disk of a planet. Upon his discovery of this nebula, Herschel wrote, “Beautiful, brilliant, planetary disk ill defined, but uniformly bright, the light of the colour Jupiter… 1′ in diameter”.
A century later, the diligent amateur Admiral William Smyth wrote, “From
its size, equable light, and colour, this fine object resembles Jupiter.”
But it may have been Robert Burnham who first referred to this nebula as the “Ghost of Jupiter”. Though to many, the greenish hue of the nebula, caused by raving-hot oxygen atoms set aglow by the dying star, makes the nebula look more like Uranus than Jupiter. See for yourself… it’s a lovely sight and well worth close inspection on an early spring night.
The nebula lies about 1,600 light years away, and spans 0.5 light years. The central star of the nebula shines at a dim magnitude 12.5. Its central core glows at 90,000 Kelvin; it will soon settle down as a slowly-cooling white dwarf.
The “Ghost of Jupiter” deserves at least as much attention as the more famous Ring Nebula in the constellation Lyra. Like the Ring Nebula, NGC 3242 is also a planetary nebula, the last hurrah of a star that’s run out of fuel and approaches the end of its life as a white dwarf. But at a relatively bright magnitude 7.3, NGC 3242 is at least 2 magnitudes brighter than the Ring Nebula, and not much harder to find. Look for it about 2 degrees southwest of the star μ (mu) Hydrae (see map below).
Click on map for larger view.
Observation notes:
In a small telescope it appears as small, oval disk that bears a close resemblance to Jupiter (hence the name). It was H. Smyth who first noted this resemblance. Like most bright planetary nebulae, the Ghost appears pale blue or green to the eyes of most observers.
In a 6-inch it appears as an oblong disc of unusually high surface brightness and sharp, well defined edges. For those with access to
larger-aperture instruments, NGC 3242 has an abundance of delightful detail in store. Burnham wrote, "There is a bright, strongly elliptical inner ring which strikingly resembles the outline of a human eye; this feature measures 26" x 16" and is oriented southeast to northwest." The central star is about 12th magnitude and sits right at the center of the elongated inner ring, completing the "Eye", another apt name for this wonderful object.
I observed NGC 3242 in an 17.5-inch Dob in July 2000. Here are my notes from that session: At 425x The Ghost took on an appearance quite similar to that of NGC 1535 (Cleopatra's Eye) and NGC 2392 (The
Eskimo). Once again I found myself looking at a large oval with a bright,
elongated ring surrounding the central star. I'm always struck by how sharp the outer edges of this one are. The surface brightness of this planetary is higher than the other two; the inner-ring detail was not quite as obvious as that of NGC 1535, but much more easily visible than that of the Eskimo. This is one of those objects worth returning to again and again, regardless of the instrument. According to many observers, 'The Ghost' shows a large improvement using UHC and OIII filters. For the UHC, some friends have found "much higher contrast with faint circular outer halo-like shell beyond the two inner shells now visible." And for the OIII, "much darker background but the two inner shells really blaze out."
In a small telescope it appears as small, oval disk that bears a close resemblance to Jupiter (hence the name). It was H. Smyth who first noted this resemblance. Like most bright planetary nebulae, the Ghost appears pale blue or green to the eyes of most observers.
In a 6-inch it appears as an oblong disc of unusually high surface brightness and sharp, well defined edges. For those with access to
larger-aperture instruments, NGC 3242 has an abundance of delightful detail in store. Burnham wrote, "There is a bright, strongly elliptical inner ring which strikingly resembles the outline of a human eye; this feature measures 26" x 16" and is oriented southeast to northwest." The central star is about 12th magnitude and sits right at the center of the elongated inner ring, completing the "Eye", another apt name for this wonderful object.
I observed NGC 3242 in an 17.5-inch Dob in July 2000. Here are my notes from that session: At 425x The Ghost took on an appearance quite similar to that of NGC 1535 (Cleopatra's Eye) and NGC 2392 (The
Eskimo). Once again I found myself looking at a large oval with a bright,
elongated ring surrounding the central star. I'm always struck by how sharp the outer edges of this one are. The surface brightness of this planetary is higher than the other two; the inner-ring detail was not quite as obvious as that of NGC 1535, but much more easily visible than that of the Eskimo. This is one of those objects worth returning to again and again, regardless of the instrument. According to many observers, 'The Ghost' shows a large improvement using UHC and OIII filters. For the UHC, some friends have found "much higher contrast with faint circular outer halo-like shell beyond the two inner shells now visible." And for the OIII, "much darker background but the two inner shells really blaze out."
Object: NGC 3242 Planetary Nebula “Ghost of Jupiter” – Artist: Serge Vieillard – Sketch Date: May 2010
Leviathan's Deep Sky Object of the Week #8: Thor's Helmet
NGC 2359
Alternative Designations: GUM 4, LBN 227.66-00.09, SH 2-298,
GRS 227.80 -00.20, LBN 1041, RCW 5
Object Type: Emission Nebula
Type Wolf - Rayet Star, with excited ejected shell and its environs
Constellation: Canis Major
Right Ascension: 07h 18m 30s
Declination: -13° 13.8′ (deg:m:s)
Distance: 15,000 ly
Visual Brightness: 10.1 ?
Apparent Dimension: 7.2' x 2.5' of arc
GRS 227.80 -00.20, LBN 1041, RCW 5
Object Type: Emission Nebula
Type Wolf - Rayet Star, with excited ejected shell and its environs
Constellation: Canis Major
Right Ascension: 07h 18m 30s
Declination: -13° 13.8′ (deg:m:s)
Distance: 15,000 ly
Visual Brightness: 10.1 ?
Apparent Dimension: 7.2' x 2.5' of arc
NGC 2359, better known as the Thor's Helmet nebula, is actually more like an interstellar bubble, blown as a fast wind from the bright, massive star near the bubble's center sweeps through a surrounding molecular cloud. The central star is an extremely hot giant Wolf-Rayet star, thought to be in a brief, pre-supernova stage of evolution. The star is nearing the end of a series of massive ejection cycles of its outers envelope which have taken place over a relatively very short period of time. Strong stellar winds have also created shock fronts in some of the older shells of ejected gas that lie farther out. In the inner shells, fierce solar winds have blown a intensely heated bubble around the star. This interesting object actually stretches in its entirety across about 30 ly of space and lies about 15,000 light years from Earth in the constellation Canis Major.
It is one of the best known Wolf-Rayet nebular structures, along with NGC 6888, and the name Thor's Helmet is due to its remarkable resemblance to depictions of the headwear donned by the famed Norse god of thunder. The image below captures striking details of the nebula's filamentary structures. The bluish colour remarks the strong emission due to oxygen atoms in the glowing gas. In fact, it can be visually seen with telescopes of moderate aperture using an [OIII] narrow-band filter.
It is one of the best known Wolf-Rayet nebular structures, along with NGC 6888, and the name Thor's Helmet is due to its remarkable resemblance to depictions of the headwear donned by the famed Norse god of thunder. The image below captures striking details of the nebula's filamentary structures. The bluish colour remarks the strong emission due to oxygen atoms in the glowing gas. In fact, it can be visually seen with telescopes of moderate aperture using an [OIII] narrow-band filter.
Views through different telescopes:
In 6-inch or smaller instruments look for a rectangular-shaped hazy patch of sky. The challenge here is not only to see the nebula at all, but to perhaps see the associated "bubble" that lies at one end of the brighter rectangle. A UHC or OIII filter will help bring out the bubble.
A 10-inch scope will reveal much more, even without a filter. A UHC filter will reveal some of the faint arcs that extend away from the bubble. An OIII filter may show detail in the round "bubble" portion of the nebula, including arcs near the edges.
I observed Thor's Helmet with my 28-inch scope last winter and was very pleased with the view even without any enhancing filters. The bright bar which runs east/west was immediately obvious. Soon I could make out the "bubble" that lies off the northeast corner of the bar. The bubble portion was very interesting! The edges appeared brighter than the inside and they were quite sharp. The inside of the bubble seemed at once smooth and mottled. The most intriguing thing was that the character of the light from the bubble was distinctly different from that of the bar.
In time I thought I could see a faint arc running out to the northwest from the north end of the bubble, but I couldn't convince myself that this wasn't the effect from a chain of stars. The photographs plainly show that this is real, and now I wonder if I might have been able to make out the similar bar to the southeast if I had looked for it. This observation was made without a filter under average skies. I'm certain that filters and/or an excellent night would bring out much more detail.
In 6-inch or smaller instruments look for a rectangular-shaped hazy patch of sky. The challenge here is not only to see the nebula at all, but to perhaps see the associated "bubble" that lies at one end of the brighter rectangle. A UHC or OIII filter will help bring out the bubble.
A 10-inch scope will reveal much more, even without a filter. A UHC filter will reveal some of the faint arcs that extend away from the bubble. An OIII filter may show detail in the round "bubble" portion of the nebula, including arcs near the edges.
I observed Thor's Helmet with my 28-inch scope last winter and was very pleased with the view even without any enhancing filters. The bright bar which runs east/west was immediately obvious. Soon I could make out the "bubble" that lies off the northeast corner of the bar. The bubble portion was very interesting! The edges appeared brighter than the inside and they were quite sharp. The inside of the bubble seemed at once smooth and mottled. The most intriguing thing was that the character of the light from the bubble was distinctly different from that of the bar.
In time I thought I could see a faint arc running out to the northwest from the north end of the bubble, but I couldn't convince myself that this wasn't the effect from a chain of stars. The photographs plainly show that this is real, and now I wonder if I might have been able to make out the similar bar to the southeast if I had looked for it. This observation was made without a filter under average skies. I'm certain that filters and/or an excellent night would bring out much more detail.
Check my Observer's Resources Page for more detailed finder charts for NGC 2359 ( Thor's Helmet)
Leviathan's Deep Sky Object of the Week: #6 NGC3115
Alternative Designations: Bennett 42, Caldwell 53, the Spindle Galaxy
Object Type: Lenticular Galaxy ( Type S(0) )
Constellation: Sextans
Right Ascension: 10h 05m 14.0s
Declination: -7° 43′ 07" (deg:m:s)
Distance:31.6 ± 1.3Mly
Visual Brightness: 9.9
Apparent Dimension: 7.2' x 2.5' of arc
Object Type: Lenticular Galaxy ( Type S(0) )
Constellation: Sextans
Right Ascension: 10h 05m 14.0s
Declination: -7° 43′ 07" (deg:m:s)
Distance:31.6 ± 1.3Mly
Visual Brightness: 9.9
Apparent Dimension: 7.2' x 2.5' of arc
Also known as the Spindle Galaxy, and Caldwell 53, this is a lenticular galaxy (type S0) in the constellation Sextans. This means it is "spiral galaxy without spiral structure", i.e. a smooth disk galaxy, where stellar formation has stopped because the interstellar matter was used up. From their appearance and stellar contents, lenticular galaxies can often hardly be distinguished from ellipticals observationally. NGC 3115 was discovered in 1787 by William Herschel.
NGC 3115 was the fourth galaxy in which a supermassive black hole was found (Kormendy & Richstone 1992, ApJ, 393, 559). It is well suited to the black hole search: at a distance of only 32 million light-years (9.7 Mpc), it is close enough that the effects of a black hole on nearby stars are easily seen, and it is transparent (no dust) and made of old stars so that the measurements are straightforward. Also, it contains an edge-on nuclear disk of stars. This is important because it means that the dynamics are dominated by rotation. As a result, the central mass can be measured with fewer uncertainties than normal. In fact, the black hole in NGC 3115 was one of the easiest to find, because it is unusually massive compared to the rest of the galaxy. Rapid rotation and large random velocities of the stars near the center imply that NGC 3115 contains a black hole about 1 billion times as massive as our Sun.
John Dreyer, astronomer and compiler of the NGC catalogue, calls this lenticular galaxy very bright (mag 9.7), large (8.3'x3.2'), very much elongated (P.A. 46°), and brightening sharply to a brightened, elongated nucleus. It lies 4.8° north of Lambda Hydrae. North is to the right in the 15 x 10 arcmin field of view shown above.
NGC 3115 was the fourth galaxy in which a supermassive black hole was found (Kormendy & Richstone 1992, ApJ, 393, 559). It is well suited to the black hole search: at a distance of only 32 million light-years (9.7 Mpc), it is close enough that the effects of a black hole on nearby stars are easily seen, and it is transparent (no dust) and made of old stars so that the measurements are straightforward. Also, it contains an edge-on nuclear disk of stars. This is important because it means that the dynamics are dominated by rotation. As a result, the central mass can be measured with fewer uncertainties than normal. In fact, the black hole in NGC 3115 was one of the easiest to find, because it is unusually massive compared to the rest of the galaxy. Rapid rotation and large random velocities of the stars near the center imply that NGC 3115 contains a black hole about 1 billion times as massive as our Sun.
John Dreyer, astronomer and compiler of the NGC catalogue, calls this lenticular galaxy very bright (mag 9.7), large (8.3'x3.2'), very much elongated (P.A. 46°), and brightening sharply to a brightened, elongated nucleus. It lies 4.8° north of Lambda Hydrae. North is to the right in the 15 x 10 arcmin field of view shown above.
Leviathan's Deep Sky Object of the Week: #4 NGC2841
Alternative Designations: UGC 4966, PGC 26512
Object Type: Flocculent Spiral Galaxy Type: SA(r)b
Constellation: Ursa Major
Right Ascension: 9h 22m 02.6s
Declination: +50° 58′ 35″ (deg:m:s)
Distance: 46 Mly
Visual Brightness: 10.0
Apparent Dimension: 8′.1 × 3′.5 of arc
Object Type: Flocculent Spiral Galaxy Type: SA(r)b
Constellation: Ursa Major
Right Ascension: 9h 22m 02.6s
Declination: +50° 58′ 35″ (deg:m:s)
Distance: 46 Mly
Visual Brightness: 10.0
Apparent Dimension: 8′.1 × 3′.5 of arc
NGC 2841 is a very delicate spiral galaxy with tightly wound arms. This galaxy is estimated to be 130,000 light years across (the Milky way is 100,000) and around 46 million light years away.
A bright cusp of starlight marks the galaxy's center. Spiraling outward are dust lanes that are silhouetted against the population of whitish middle-aged stars. Much younger blue stars trace the spiral arms.
Notably missing are pinkish emission nebulae indicative of new star birth. It is likely that the radiation and supersonic winds from fiery, super-hot, young blue stars cleared out the remaining gas (which glows pink), and hence shut down further star formation in the regions in which they were born. NGC 2841 currently has a relatively low star formation rate compared to other spirals that are ablaze with emission nebulae.
Star formation is one of the most important processes in shaping the universe. It plays a pivotal role in the evolution of galaxies, and it is also in the earliest stages of star formation that planetary systems first appear.
Yet there is much that astronomers don't understand, such as how the properties of stellar nurseries vary according to the composition and density of the gas present, and what triggers star formation in the first place. The driving force behind star formation is particularly unclear for a type of galaxy like the flocculent spiral s which features short spiral arms rather than prominent and well-defined galactic limbs.
This galaxy has also had a history of supernovae explosions within it, the most recent going off in 1999.
The galaxy can be found in the front legs of Ursa Major (the Big Bear) which lies almost directly overhead by 10:30 pm in early-mid April. Click on the diagram for a bigger view of the finder chart below.
A bright cusp of starlight marks the galaxy's center. Spiraling outward are dust lanes that are silhouetted against the population of whitish middle-aged stars. Much younger blue stars trace the spiral arms.
Notably missing are pinkish emission nebulae indicative of new star birth. It is likely that the radiation and supersonic winds from fiery, super-hot, young blue stars cleared out the remaining gas (which glows pink), and hence shut down further star formation in the regions in which they were born. NGC 2841 currently has a relatively low star formation rate compared to other spirals that are ablaze with emission nebulae.
Star formation is one of the most important processes in shaping the universe. It plays a pivotal role in the evolution of galaxies, and it is also in the earliest stages of star formation that planetary systems first appear.
Yet there is much that astronomers don't understand, such as how the properties of stellar nurseries vary according to the composition and density of the gas present, and what triggers star formation in the first place. The driving force behind star formation is particularly unclear for a type of galaxy like the flocculent spiral s which features short spiral arms rather than prominent and well-defined galactic limbs.
This galaxy has also had a history of supernovae explosions within it, the most recent going off in 1999.
The galaxy can be found in the front legs of Ursa Major (the Big Bear) which lies almost directly overhead by 10:30 pm in early-mid April. Click on the diagram for a bigger view of the finder chart below.
Leviathan's Deep Sky Object of the Week: #3: M61: Spiral Galaxy
M61 is a barred spiral galaxy located in the southern extremity of the nearby Virgo Cluster of Galaxies (the nearest supercluster of galaxies in the universe to our own Milky Way galaxy). Visible in M61 are a host of features common to spiral galaxies: bright spiral arms, a central bar, dust lanes, and bright knots of stars. M61 is believed to be quite similar in appearance to our own Milky Way Galaxy. M61 was discovered by telescope in 1779 twice on the same day, but one observer initially mistook the galaxy for a comet. Light from M61 takes about 53 million years to reach us although this measurement is difficult to confirm due to issues in measuring redshift effects in the massive gravitational field of the Virgo supercluster. Another noteable feature of this galaxy is that recent observations of M61 have detected unpredicted high velocity gas moving in its halo.
M61 is one of the larger galaxies in the Virgo cluster; its 6 arc minutes of diameter correspond to about 100,000 light years, similar to the diameter of the Milky Way galaxy. (SEDS) It is classified as a SABbc spiral galaxy.
The galaxy is also notable astrophysically for having had 6 supernova observed in it, which apparently ties it with M83 as the Messier galaxy with the most observed supernova, but none of the supernova in M61 have been of the Type1a used to measure cosmological distances.
See the finder chart on the finder chart and resources page for a more detailed map on how to find this little beauty.
M61 is one of the larger galaxies in the Virgo cluster; its 6 arc minutes of diameter correspond to about 100,000 light years, similar to the diameter of the Milky Way galaxy. (SEDS) It is classified as a SABbc spiral galaxy.
The galaxy is also notable astrophysically for having had 6 supernova observed in it, which apparently ties it with M83 as the Messier galaxy with the most observed supernova, but none of the supernova in M61 have been of the Type1a used to measure cosmological distances.
See the finder chart on the finder chart and resources page for a more detailed map on how to find this little beauty.
Leviathan's Deep Sky Object of the Week: #1: M22, the Great Sagittarius Globular Cluster
Alternate Designations: NGC 6656, GCl 99
Constellation: Sagittarius
Right ascension: 18h 36m 23.94s
Declination: –23° 54′ 17.1″
Apparent dimension: (V) 32 arcmins
Apparent magnitude (V) 5.1
Classification: VII (elliptical)
Distance: 10.6 ± 1.0 kly Estimated age: 12 Gyr
Estimated Mass: 2.9×105 M☉ Estimated Radius: 50 ± 5 ly
Constellation: Sagittarius
Right ascension: 18h 36m 23.94s
Declination: –23° 54′ 17.1″
Apparent dimension: (V) 32 arcmins
Apparent magnitude (V) 5.1
Classification: VII (elliptical)
Distance: 10.6 ± 1.0 kly Estimated age: 12 Gyr
Estimated Mass: 2.9×105 M☉ Estimated Radius: 50 ± 5 ly
M22 is one of the nearer globular clusters to Earth at a distance of about 10,600 light-years away. It spans 32' on the sky which translates to a spatial diameter of 99 ± 9 light-years. 32 variable stars have been recorded in M22. It is projected in front of the galactic bulge and is therefore useful for its microlensing effect on the background stars in the bulge.
Despite its relative proximity to us, this metal-poor cluster's light is limited by dust extinction, giving it an apparent magnitude of 5.1 making it the brightest globular cluster visible from mid-northern latitudes (e.g. Europe and most of North America). However, due to its southerly declination, M22 never rises high in the sky and so appears less impressive than other summer sky globulars such as M13 and M5.
Despite its relative proximity to us, this metal-poor cluster's light is limited by dust extinction, giving it an apparent magnitude of 5.1 making it the brightest globular cluster visible from mid-northern latitudes (e.g. Europe and most of North America). However, due to its southerly declination, M22 never rises high in the sky and so appears less impressive than other summer sky globulars such as M13 and M5.
M22 is very unusual in that it is one of only four globulars (the others being M15, NGC 6441 and Palomar 6) that are known to contain a planetary nebula. It was discovered using the IRAS satellite by Fred Gillett et al.,in 1986 as a pointlike source (IRAS 18333-2357)[14] and subsequently
identified as a planetary nebula in 1989 by Gillett et al.[15] The planetary nebula's central star is a blue star. The planetary nebula (designated GJJC1) is estimated to be a mere ~6,000 years old.
Because of its visual brightness, the cluster is relatively easy to find just to the east of the tip of the "teapot" of Sagittarius. When viewed at medium to high power, the core of the cluster resolves into a jewel box of diamond-like points sparkling on a hazy cloud of unresolved thousands more. Look for dark lanes among the chains of stars spreading from the core.
This cluster is thought to contain up to 3,000,000 stars! It is truly a gem of the summer sky!
identified as a planetary nebula in 1989 by Gillett et al.[15] The planetary nebula's central star is a blue star. The planetary nebula (designated GJJC1) is estimated to be a mere ~6,000 years old.
Because of its visual brightness, the cluster is relatively easy to find just to the east of the tip of the "teapot" of Sagittarius. When viewed at medium to high power, the core of the cluster resolves into a jewel box of diamond-like points sparkling on a hazy cloud of unresolved thousands more. Look for dark lanes among the chains of stars spreading from the core.
This cluster is thought to contain up to 3,000,000 stars! It is truly a gem of the summer sky!
Very bright, Messier 22 is one of the few globular clusters that can be seen with the naked eye from dark sky locations. (click on image to enlarge)