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For of us in the Northern Hemisphere, the hours of darkness are rapidly departing, in anticipation of later June's Summer Solstice.  By late May, many observers in temperate northern latitudes will be experiencing permanent astronomical twilight.  But never fear - there are still plenty of targets in this month's sky guide that can be well seen, even if you're lacking true darkness.  Of course, for our temperate southern hemisphere readers exactly the opposite is true - you'll now be in the run up to the darkest part of the year.  Wherever you find yourself in the world, keep looking up - as ever, there's lots to see in the skies above us this month.

 

The Solar System

 

The Moon

 

The Moon begins May in Pisces as a Waning Crescent of around 11% illumination. You can catch the Moon in the predawn sky, sitting a little to the west of the striking Venus and much fainter and more difficult Mercury, on the morning of the 1st. 

 

New Moon occurs four days later, when the Moon slides to the south of the Sun in Aries, after which it becomes an evening object. 

 

This Evening Crescent phase of the Moon in May leads to one of the best chances to observe the Crescent Moon at greatest separation from the horizon for northern hemisphere observers. With the Moon in the constellation of Gemini - the most northerly part of the ecliptic - during the immediate run up to First Quarter, this should give us in the temperate northern hemisphere a great chance to observe the Moon’s eastern hemisphere. 

 

Crescent Moon at sunset, May 9th.  Image created with SkySafari 5 for Mac OS X, ©2010-2016 Simulation Curriculum Corp., skysafariastronomy.com.

 

The Moon reaches First Quarter in the 12th while in Leo, having just clipped M44, The Beehive Cluster in neighbouring Cancer just before it sets from Europe in the early morning of the 11th. 

 

The Moon then slides gently south, down the other side of the ecliptic, until it reaches Full in Libra on the 18th. 

 

On the late evening/early morning of the 20th/21st, the Waning Gibbous Moon rises alongside Jupiter in the sky, the two forming a striking pair. Our natural satellite forms a lose pairing with neighbouring Saturn on the morning of the 23rd. 

 

The Moon comes to Last Quarter in Aquarius on 26th May, before ending the month much as it started, on the 31st as a thin 11% illuminated Crescent in Pisces.  

 


Mercury 

 

The Innermost Planet starts the month rising in Pisces in the morning sky just before the Sun and practically in line with it from a temperate northern hemisphere perspective. At -0.3 magnitude and 5.8 arc seconds across, it would be fairly difficult to spot if higher in elevation, but it will be impractical to observe it unless you are much further south in the equatorial regions of our planet. 

 

As May progresses, Mercury heads eastwards towards the Sun, increasing in brightness, but this will make viewing it even more difficult, even from the tropics. 

 

Mercury reaches superior conjunction with the Sun on the 21st May, appearing to pass fractionally to the north of the solar disk, before re-emerging as an evening target. 

 

Mercury at Superior Conjunction, 21st May.  Image created with SkySafari 5 for Mac OS X, ©2010-2016 Simulation Curriculum Corp., skysafariastronomy.com.

 

Mercury ends the month in the eastern part of Taurus, still close to the Sun, but set up for a great evening apparition in the latter part of June. 

 


Venus

 

At -3.9 magnitude at the month’s beginning, Venus is, as ever, a brilliant target. However, it shares a similar observing fate with neighbouring Mercury, with which it shares the constellation of Pisces at this time. Venus is slightly higher at sunrise than Mercury appears and its brilliance means it may be more possible to pick out in the dawn sky, but will still be desperately low for those of us in the temperate northern hemisphere. Atmospheric distortion means it will be unrewarding to observe at any great magnification and at 88% illumination and 11.5 arc seconds diameter the planet isn’t at its best. 

 

Venus at sunrise, 1st May.  Image created with SkySafari 5 for Mac OS X, ©2010-2016 Simulation Curriculum Corp., skysafariastronomy.com.

 

By mid-month Venus’ situation hasn’t changed much. On the 17th it crosses the border into Aries.  The planet will stand under 6 degrees in elevation in the east as the Sun rises (from latitude 51 degrees N), so will remain a challenging and rather unrewarding target.  Venus comes into conjunction with Uranus around the 18th and 19th May, with the two bodies separated by around 1 1/4 degrees, though chances of seeing the two together are nil - at +5.9 mag, Uranus is far too faint to be picked out in the dawn sky.

 

By the end of the month, Venus can be found just over 20 degrees from the Sun, still at -3.9 mag and standing 6 degrees high at sunrise (from latitude 51 degrees N).

 

Mars

 

The Red planet can be found amongst the stars of eastern Taurus as May begins.  At +1.6 mag and 4.2 arc seconds across it isn’t at its most inspiring, to put it mildly.  Standing just over 30 degrees high from the horizon at sunset (from latitude 51 degrees N), Mars will be easy enough to find, situated between the horns of Taurus, but observers will need pretty hefty magnification to see much of its disk.  Here on Earth, we are now just under 336 million km from Mars - a distance that is getting larger by the day. Although we’re some way off Martian superior conjunction from our perspective here on Earth (this occurs this September), the trend will continue to be downwards in brightness, apparent diameter and subsequent ease of observation, until quite some time after this.

 

Relative positions of planets in the Inner Solar System, early May.  Image created with SkySafari 5 for Mac OS X, ©2010-2016 Simulation Curriculum Corp., skysafariastronomy.com.

 

By mid-month, on the 15th, Mars has dropped to +1.7 mag and now presents a 4 arc second diameter disk.  The following day it crosses over the border from Taurus into Gemini, entering the most northerly part of the ecliptic.  Setting about three hours after the Sun, Mars stands 25 degrees high in the west after sunset.  On the early evening of the 19th, Mars enters the boundaries of the lovely open cluster M35.  This event will be visible in telescopes and larger binoculars, though as both objects will only be just under 24 degrees high from the horizon (from latitude 51 degrees N), as the Sun sets, the circumstances for observing this event aren’t ideal.  While Mars is pretty far from Earth at this point, M35, at 3000 light years away from us, is distinctly the further of the two.

 

At the month’s end, Mars has dropped in brightness fractionally to +1.8 mag and now presents a tiny 3.8 arc second diameter disk.  Standing around 9 degrees high in the west as the Sun sets (from latitude 51 degrees N), the Red Planet will take a little hunting out in the twilight from various environments.  It will now set around 2 1/2 hours after the Sun does.

 

 

Jupiter

 

The King of the Planets is coming up to opposition in early June and as such, approaches its best during May.  Rising at just before midnight on the 1st, Jupiter presents a 43.5 arc second angular diameter, shining at an unmissable -2.5 mag - clearly brighter than anything else in its particular patch of sky.  Now a resident in the non-zodiacal constellation of Ophiuchus, Jupiter is not fantastically well-placed for northern hemisphere observers.  Reaching an angular height of just over 16 degrees as it transits in the south (from latitude 51 degrees N), the planet will be subject to atmospheric extinction and at the mercy of haze for those attempting high power observations.  However, Jupiter is always worth a look, even if you have to use more modest upper ranges of magnification than you would do, were the planet higher in the sky.

 

Early in the morning of the 13th, there’s a nice simultaneous GRS and Io and Io shadow transit, as the planet is transiting from Western Europe, which although it occurs at just after 3am, will be a rewarding sight to see.  By mid-month, Jupiter is still -2.5 mag, though has increased a tiny amount in diameter to 44.8 arc seconds.

 

Jupiter with GRS and Io Transit and Shadow Transit, 3am, 13th May.  Image created with SkySafari 5 for Mac OS X, ©2010-2016 Simulation Curriculum Corp., skysafariastronomy.com.

 

By the end of the month, Jupiter has brightened to -2.6 magnitude and is now just under 46 arc seconds in diameter.  The planet will rise at just after 9.40pm and transit at around 1.45am the following morning.  At the end of May, Jupiter is 10 days off opposition, so make the most of the best couple of months of Jovian observations that this year allows us - even if it means staying up until the small hours to do so.

 

 

Saturn

 

Saturn begins May by going retrograde - appearing to reverse its regular west-to-east direction within the ecliptic.  This retrograde motion occurs to all the outer planets in the lead up to opposition (which in Saturn’s case occurs in early July).  Of course the planet is emphatically not changing direction itself, rather that we on Earth are catching up the outer planet on our faster interior orbit.  A basic analogy is that of overtaking - or more correctly, undertaking - a car on a motorway.  Once we have caught up with a car, it appears to move “backwards” from our perspective, even though both vehicles are travelling in the same direction.

 

At +0.5 mag and 17.2 arc seconds diameter, Saturn is a healthy size. Although much fainter than Jupiter in neighbouring Ophiuchus, Saturn is still brighter than any stars in Sagittarius, the zodiacal constellation it is resident in. Sagittarius is, of course, the most southerly of all the constellations of the ecliptic, so the Ringed Planet isn’t fabulously-places from a northern hemisphere perspective, but still well worth seeking out in the morning skies.  Saturn rises at just after 1.45am on the 1st and transits around four hours later, when it will reach an altitude of a little under 17 1/2 degrees (from latitude 51 degrees N).

 

By mid-May, Saturn has brightened fractionally to +0.4 mag and is now 17.6 arc seconds across. 

 

Saturn and Major Moons, Transit point, 15th May.  Image created with SkySafari 5 for Mac OS X, ©2010-2016 Simulation Curriculum Corp., skysafariastronomy.com.

 

On the 22nd the Moon will occult Saturn, but this event will only be seen by residents of Southern Africa. 

 

By the end of the month, Saturn was brightened yet further to +0.3 magnitude and is now 18 arc seconds in angular size. Rising at a little before midnight, this perennial jewel of the night sky transits at just before 4am. 

 

 

Uranus and Neptune 

 

Both the outer gas giants are poorly placed for observation during May. Uranus is still emerging from its recent superior conjunction and is still lost in morning twilight. Neptune, further west in the ecliptic is slightly better placed, but being much fainter than Uranus will in all likelihood be just as much of a challenge to observe. It will be the latter part of the year before both are in a better position for observing. 

 

 Uranus and Neptune at dawn, 15th May.  Image created with SkySafari 5 for Mac OS X, ©2010-2016 Simulation Curriculum Corp., skysafariastronomy.com.

 

 

Comets

 

There are no particularly bright comets observable at present. Comet Iwamoto is fading fast, after its race past us earlier in the year and the next potentially bright comet, 2017 T2 (PanSTARRS), is poorly-placed and will not be at its best until the autumn.   The brightness prediction for this comet ranges from an exciting -1.5 magnitude, to a distinctly less impressive +7.5 mag - quite a difference. It will be interesting to see how this object develops, though as ever, it’s pointless getting excited about a comet until it is exciting. We’ll keep you posted on this one. 

 


Meteors

 

The Eta Aquariids, fed by the famous Halley’s Comet, come to the fore on May 6th. This shower is usually modest in peak Zenithal Hourly Rates, reaching about 20 meteors per hour, though can sometimes exceed three times this rate. 

 

This year the Moon is almost perfectly placed out of the way, at just a day past New, as the Eta Aquariids peak, which will make for ideal conditions for observing and photographing the event. The radiant rises at a little after 2.30am, so it is often observed that the shower is better-seen from the Southern Hemisphere, where the radiant rises higher. However, meteors can appear in any part of the sky, fanning out from their radiant source, so those of us in the northern hemisphere shouldn’t be put off. 

 

Eta Aquariids radiant.  Image created with SkySafari 5 for Mac OS X, ©2010-2016 Simulation Curriculum Corp., skysafariastronomy.com.



Deep Sky Delights in Coma Berenices and The Bowl of Virgo

 

This month, galaxy season continues, as we examine the contents of Coma Berenices and the Bowl of the much larger Virgo.  This area of sky is the most galaxy rich in the entire heavens - as it is the direction in which the Virgo Supercluster of galaxies lies.  The Virgo Supercluster is one of the largest structures known in the entire Universe and directly affects us, lying within the Milky Way.  Indeed, it is arguable that our Local Cluster of galaxies, to which the Milky Way, M31, M33 and others belong are an outlying part of this larger structure.  Although the distances to many of these objects are vast, they are linked to us - quite a sobering thought.  

 

On a lighter note, seeing this area of sky well-positioned in the evening time really gives one a feeling that Summer is just around the corner, for those in the Northern Hemisphere - though for those in higher Northern latitudes, this has to be balanced with the rapidly diminishing hours of true darkness in which to observe.  

 

Coma Berenices and the bowl of Virgo.  Image created with SkySafari 5 for Mac OS X, ©2010-2016 Simulation Curriculum Corp., skysafariastronomy.com.


Coma Berenices is a rather poor constellation, containing three major stars of the 4th magnitude.  However, what it lacks in brightness, it more than makes up for in deep sky objects.  This first of these is not a galaxy, it's actually an open star cluster - Melotte 111.  This collection of around 40 stars is loosely gathered over a 4 1/2 degree area and was first noted by Ptolemy in around 138CE.  This hazy collection is visible to the naked eye from a good site, and although once represented as the tail of neighbouring Leo, was re-classified by Ptolemy as a constellation in its own right, representing the legend of the Egyptian Queen Berenice's hair which was sacrificed to the goddess Aphrodite in return for the safe return of the Queen's husband Euergetes.  Legend has it that Aphrodite was so pleased by the gift that she placed it in the sky for all to see - hence the constellation's title, Coma Berenices - or Berenice's Hair.  

 

In reality, Melotte 111 lies around 300 light years away from us, making it the third closest star cluster to us, after the asterism of the Plough or Big Dipper in Ursa Major and the Hyades in Taurus.  Somewhat curiously, Meotte 111 is neither receding or approaching us, rather keeping pace with our position in our mutual journey around the Milky Way galaxy.

 

Melotte 111 - taken from the ISS by astronaut Donald R. Pettit.  Public Domain - NASA/Donald R. Pettit


Due to its large size, Melotte 111 is best seen in low power binoculars or by the naked eye.  However, wide field images of the area reveal it well.

 

Just under a degree and a half from the Eastern edge of Melotte 111, sits the elliptical galaxy NGC4494.  This 4.8 x 3.5 arc minute object is +9.80 mag and t is somewhat bland in appearance, though can be seen in instruments of many sizes.

 

The same cannot be said of NGC4494's neighbour, the spectacular NGC4565, otherwise known as the Needle Galaxy.  This +9.60 mag, 15.8 x 2.1 arc minute edge on spiral is a delight in larger instruments and has surface brightness high enough to be seen in many smaller instruments.  Discovered by William Herschel in 1785, NGC4494 is much beloved of astronomers, and is often considered the Springtime equivalent of the Autumnal NGC891 in Andromeda.  A large dust lane intersects the galaxy right down its major axis - this lane can clearly be seen in telescopes of 8-inch aperture and above in notable relief against the glow of the galaxy's centre.  However, this galaxy is well worth seeking out no matter what size your telescope is. 

The Needle Galaxy.  Image credit - Mark Blundell. Image used by kind permission.


Three and 3/4 degrees to the N of NGC4494, sit a pretty, if rather fainter (at +10 mag) spiral galaxy - NGC 4559.  This spiral is 10.7 x 4.4 arc minutes in size and rather lower in surface brightness than its better-known neighbour.  It is thought to lie some 35 million light years away from us.

NGC4559. Image Credit: Roberto Mura.  Public Domain.


NGCs 4278 and 4414 lie to the NW and N of NGC4494, both equidistant by about 3 3/4 degrees.  An elliptical and a spiral galaxy respectively, these are rather compact targets and worth seeking out if you have a larger telescope.  Though part of the greater Coma cluster of galaxies, they lie further away from us at around 55 and 58 million light years distance. 

 

NGC4278 - Hubble Space Telescope Image. Image Credit: Nasa/ESA Public Domain.


Moving down diagonally SE through NGC4494, by about 4 degrees, we come to the pretty spiral galaxy NGC4725.  This 10.7 x 7.6 arc minute object sits at +9.39 mag  and displays a prominent central bar, around which loops a bright halo.  NGC4725 is somewhat of an oddity, having just one enormous continuous spiral arm, which appears to loop round itself 3 1/2 times.  Most spiral galaxies display at least two arms, so NGC4725 is a rarity.  It8 lies some 40 million light years from us.

NGC4725 and surrounding galaxies. Image Credit: Mark Blundell.


Another 4 degrees SE of NGC4725 lies one of Coma's highlights, and much beloved of imagers and visual observers alike - the marvellous M64 - otherwise known, for reasons that will be obvious to all those who see it, as the Black Eye Galaxy.

 

First discovered in 1779, by astronomer Edward Pigott, M64 was independently found by Messier the following year.  This +8.5 mag, 10 x 5.4 arc minute object can be found in small telescopes and even powerful binoculars from a good site.  The reasons for its nickname will become apparent to all those who glimpse it through a more powerful scope: M64 has a large dark dust lane encircling its core, which stands out in stark contrast to the soft glow of its interior.  It does indeed look somewhat like a black eye - albeit a rather large one on the cosmic scale..  M64 lies relatively close to us - some 17 million light years - but is a rather diminutive spiral galaxy , which is wreathed in a larger out halo of stars, thought to be the remnants of an absorbed satellite galaxy.  This halo appears to rotate in the opposite direction to the main body of M64 and may be responsible for the compression of the dark black eye feature, making it more prominent to outside observers than it would be otherwise.  M64 is a very rewarding target for astrophotographers as Mark Blundell's photo shows.  Don't miss this rewarding target, whatever optical aid you employ.

M64. Image Credit: Mark Blundell


Just over 5 degrees further SE from M64, lies a lovely globular cluster, M53.  Discovered in 1775 by Bode and catalogued by Messier 2 years later, M53 is 2.6 arc minutes in diameter and +7.6 mag in brightness.  While not quite as prominent as other major globulars, this is easily seen in telescopes of any size and also shows up in binoculars.  Larger telescope will resolve its core well, but M53 is really a victim of its distance from us - some 58,000 light years away.  When compared to M13 in Hercules, at 25,000 light years distance, M53 seems quite distant.  

M53 - Hubble Image.  Image Credit: Nasa/ESA. Public Domain.


Next door, by a degree to the E, is a much slightly larger and poorer globular, NGC5053.  At +9.47 mag brightness and 5.2 arc minutes diameter, this is a much more difficult object than its more illustrious neighbour, though is fairly easy to find due to its proximity.  Both globulars are approaching us at around 79 km per second.

 

11 degrees to the W of M64, sits the large lentinicular galaxy M85.  At +9.1mag and 7.1 x 5.5 arc minutes in angular size, M85 has a bright, compact core, surrounded by a rather uniform ring of stars.  Shining at +9.10 mag it is easy visible, but M85 is presented much more face on and is thus fainter.  This galaxy has a rather elderly stellar population, a trait it shares with other lentiniculars.  M85 was discovered in 1781 by the prolific Pierre Mechain and added to the Messier list by Charles Messier later that year. 

M85, Hubble Image.  Image Credit: Nasa/ESA. Public Domain.

 
Two and a half degrees to the South of M85 is the fabulous M100 - one of the best Spiral Galaxies in the sky.  Discovered in the same year as M85, by the same man (Mechain), M100 is often described as a "Grand Design Spiral" - a very well defined galaxy with particularly prominent arms.  Of this definition, as far as M100 is concerned, there can be no doubt: at +9.39 mag and 7.5 x 6. arc minutes of size, it is easily within reach of small telescopes and its spiral arms will begin to be glimpsed by small telescopes under good conditions.  Observers will note M100's elongated oval core being surrounded by a fainter halo of stars.  Larger instruments will begin to resolve the finer details of this beautiful galaxy's spiral structure.  M100 is to be found 47 million light years distance from us and has also been noted for its star bursting nature.  Rapid star formation is occurring within the galaxy, with energetic bright blue stars being in abundance.  Though it is not only for star formation that M100 is notable: during the 20th Century, four supernovae were witnessed to take place within the galaxy.  The only supernova of this century to be observed in m100 occurred in 2006.  M100 is one of the jewels of this area of sky and should not be missed.

M100, European Southern Observatory Image.  Image Credit: ESO, Creative Commons.


Another two and a half degrees to the SW of M100 lies another treat for fans of spiral galaxies, the lovely M98.  At +10.10 mag, it is not especially bright for a Messier list object (remember, most of the members of this list were discovered with a 2.5-inch refractor).  But whereas M100 is presented face on, M98 shows a very different, foreshortened aspect, which concentrates its light.  At 9.8 x 2.8 arc minutes in  dimensions, M98 is longer, yet substantially thinner than its neighbour and a barred spiral structure.  Again, this galaxy was discovered by Mechain and catalogued by Messier in 1781.  Modern observers with small telescopes will see M98 as an elongated patch of light, though those with larger instruments will begin to glimpse traces of mottling of its inner darker lanes.  Although there is still a reasonable amount of star formation going on within M98, as evidenced by a healthy young blue star population, much light output from this galaxy is shifted towards the red by the amount of dust and substantial HII regions of ionised Hydrogen - areas similar to the M42 region of our galaxy.   

M98 - European Southern Observatory Image.  Image Credit: ESO, Creative Commons.


Long duration astrophotography of M98 reveals a notable kink and trail from its leading spiral arm. This, in addition to an unusual blueshift in its spectral signature suggests that M98 may have had a recent (galaxially-speaking) encounter with neighbouring M99.  It had been suggested when this blueshift was first discovered that M98 was a much closer object than its neighbours, but this postulated tidal encounter now seems to explain this phenomenon more elegantly.

 

A degree and a third East of M98 lies the aforementioned M99, otherwise known as the Coma Pinwheel Galaxy (to differentiate it from M33 in Triangulum, confusingly known as the Pinwheel too).  Like M100 and M98, it too is a spiral galaxy, but is presented face on rather than edge on, like M98.  It is noted in some sources that Mechain discovered all three galaxies in the same night - 15th March 1781 - not bad going for an evening's observations!  

M99 - Copyright Adam Block Mount Lemmon SkyCenter University of Arizona, Creative Commons.

 
M99 is a compact (5.3 x 4.6 arc min) object of +9.89 mag.  It lies a little further from us than do its neighbours, at 53-55 million light years distance.  M99 has the distinction of being the second spiral galaxy (more accurately, Spiral nebulae) to be recognised us such by Lord Rosse, after observations in the Spring of 1846.  What Lord Rosse achieved with his enormous "Leviathan of Parsonstown" telescope, can be more easily achieved by modern instruments with more effective optics.  Roger Nelson Clarke writes of M99 in Visual Astronomy of the Deep Sky that  "In the 8-inch, the central portion appeared was a small, bright diffuse area, while the spiral arms formed a soft uniform glow around it.. …detection of the bright southern spiral arm has been reported by observers under good to excellent skies with 8-inch telescopes."  Again, detection of spiral structure in M99 (much as many of the major spiral galaxies) will really need a larger telescope (12-inches +) and really decent skies - but once seen it will not be forgotten.  

 M99's Southerly arm appears dominant and slightly further extended than the less obvious Northerly arm, giving the galaxy a somewhat lopsided appearance.  This could have been due to gravitational interaction with a number of bodies, the aforementioned M98, but more likely the nearby NGC 4262 or the exotic VIRGOHI21.  This latter object is a so-called "Dark Galaxy" - a region of gas that appears to contain a significant amount of Dark Matter - equivalent to the mass of a small galaxy - but no stars.  However, debate rages as to whether Dark Galaxies even exist, with other theories suggesting that the VIRGOHI2I region is simply a large detached area of gas from one of the galaxies in this region.  If this were so, this object should contain some stars - which confusingly it doesn't!  Further observations and theories are needed to explain exactly what is going on in this area of the cosmos.

 

Three degrees to the E of M99 lies the another attractive spiral galaxy, M88 - and another degree and a half further E is the face on barred spiral galaxy M91.  Of the two, M88 is the better object for observers with small telescopes.  Whilst it is not edge on, (some sources list it as inclined by 36 degrees, others by 64 degrees) M88 is well presented to us on Earth, its foreshortening adding to the overall surface brightness of this 6.8 x 3.7 arc minute, +9.6 mag object.  Unlike many of the previously mentioned Messier objects, M88 was actually discovered by Charles Messier, rather than Mechain, on March 18th 1781.  The spiral nature of M88 can be seen in reasonable sized instruments, given good sky conditions and generous (probably x150+) magnification.  As a good example regular spiral, this galaxy should be high on the list of potential targets in this region of sky.  M91, on the other hand, is a more problematic object.  at +10.19 mag it is amongst the faintest of the Messier list.  Indeed, it was only in the latter half of the 20th century that it was even definitively recognised as a member at all.  M91 was a supposed "missing Messier" - an object with a clear listing and description but an imprecise location.  It was only in 1969, after US amateur astronomer William C Williams followed Messier's stated directions to this object from M89, rather than the listed M58, that the mystery was brought to a close (though William Herschel had suggested it as a possible candidate nearly 200 years earlier).

M88 - Copyright Adam Block Mount Lemmon SkyCenter University of Arizona, Creative Commons.

 
Whereas M88 is of a high surface brightness, M91 as a 5.2 x 4.2 arc min face on galaxy is very low. Decent sky conditions and a larger instrument (8-inches +) will be needed to glimpse its central bar.  It is only in long duration astrophotography that this galaxy really comes alive.  Imagers will reveal the true nature of this lovely object , with its two graceful widely-sweeping arms, condensed core and generous bar.  M91 is rather poor in terms of star formation and whilst one of the larger barred spirals in the Virgo group is rather further away from us than many of the other major members, at 51-55 million light years distance.

M91. Image credit: Joseph D. Schulman, Creative Commons.


Just under a degree SSW of M88 lies the small +10.19 mag spiral galaxy of NGC 4477, which in turn marks the beginning of a glorious 1.5 degree long arc of galaxies known as Markarian's Chain.  This gently curving line of galaxies is one of the finest sights in the sky and an almost peerless photographic subject from a galaxial point of view.  

 

Markarian's Chain comprises of the aforementioned NGC 4477 at the Northerly end and the major galaxies M84 (elliptical, +9.10 mag), M86 (lentinicular, +8.89 mag), at its Southerly tip.  Galaxies NGC 4473 (elliptical +10.19 mag), NGC 4461 (spiral +11.19 mag), NGC 4458 (elliptical +12.10 mag), NGC 4438 and NGC 4435 (both spiral, +10.80 mag, together known as "The Eyes").  The Chain spills over the Coma Berenices border into Virgo, where the largest part of it resides.

 

Markarian's Chain is named after the Armenian Astrophysicist Beniamin Markarian, who in the early 1960s first suggested a common motion for all these galaxies. Observations have proved than all the above galaxies are in fact gravitationally interacting with each other, though there are outlying and closer objects  - most noticeably the spiral NGC 4388 which may or may not to be a part of the system - which also populate the area.

Markarian's Chain.  Image Credit: Mark Blundell.


Frankly, it's difficult to pick out clear highlights in Markarian's Chain, but special mention must go to the eerily-named "The Eyes" galaxy pairing of NGC 4438 and NGC 4435.  This pairing do appear like a pair of eyes peering back at an observer through the gloom and were first nicknamed this by late-19th and 20th century astronomer L.S. Copeland.  Looking at these two objects in even a relatively small telescope will confirm this nickname's accuracy - the similar galaxial core brightness and angular orientation of both objects help to complete the illusion.  Both galaxies it is clear have gone through some sort of interaction in the recent past as astrophotography reveals a large amount of stellar and dark material spilling from NGC 4438's disk.

 

A degree to the SE of the eyes lies the vast elliptical galaxy M87, otherwise known simply as Virgo A.  This enormous object is easily picked up in amateur instruments from even fairly light polluted environments, shining as it does at +8.60 mag.  M87 was discovered and catalogued by Messier in 1781.

 

To call M87 vast is to somewhat understate the case: it is estimated to be anything up to 200 times the mass of our own Milky Way galaxy and has over 12,000 globular clusters in orbit around it, compared to our galaxy's rather paltry estimated 150-200.  M87 also appears to be close to the gravitational centre of the Virgo-Coma Supercluster and may be the key gravitational driver of the whole system.  Astrophotography reveals a large jet emanating from M87's centre.  This was first recorded by Lick Observatory Astronomer H.D. Curtis in 1918 and a corresponding much fainter opposite jet was discovered in 1966.  These jets mark at their epicentre one of the most massive black holes so far postulated - a 2-3 billion solar mass object, condensed to about the volumetric size of our solar system.  It is thought to be this object that makes Virgo A one of the most energetic sources of X-Rays, Radio Waves and Gamma Rays in the sky.  

M87 - Hubble Image, showing main central jet. Image Credit: NASA/ESA, Public Domain.

 
This remarkable monster galaxy can be easily spotted in decent sized binoculars from a reasonable location and is one of the most straightforward galaxies to observe in the sky.  To give a sense of scale, M87 lies 55 million light years away and its outer extents observable from here on Earth cover an area of sky larger than the full Moon.  If put in place of M31, the Andromeda Spiral, in our skies, M87 would probably fit into an area the size of the Square of Pegasus - it's that big!  However, even the mighty M87 pales in comparison to the galaxy IC1011 (also in Virgo) which takes the prize of the largest galaxy currently known at a staggering 6 million light years across - 60 times the size of our Milky Way's 100,000 light year span.

 

Just over a degree E of M87 lies another elliptical galaxy: M89.  This Messier-discovered object is fairly bright and compact at +9.80 mag and 3.5 x 3.5 arc minutes in size.  M89 is a remarkably spherical object, or at least appears to be from our perspective.  This is unusual, as most elliptical galaxies do appear slightly elongated.  M89 is rather special in terms of its conformity.  This makes for an easily observed object in most telescopes, but unfortunately, a rather bland experience.

M89 - Hubble Image. Image Credit: NASA/ESA, Public Domain.

 
Whereas the unfortunate M89 is fairly bland, its neighbour, M90, to be found 3/4 of a  degree to the N is anything but.  At +9.50 mag and an angular size of 9.5 x 4.4 arc minutes, it is a touch difficult in binoculars in comparison with its two elliptical neighbour, but is well-seen as a elongated spiral in larger telescopes.  M90 is fairly unique amongst Messier galaxies, as its spectral shift is very pronounced towards the blue side of the spectrum, suggesting it is rapidly approaching us in relation to the rest of the cluster.  This may be due to it having broken free of the gravitational bounds of the cluster, or indeed it may be considerably closer than the 50-or-so million light years distance it is thought to lie.  Another interesting feature of M90 is that star formation appears to have ceased almost entirely within the system.  As such it is referred to as a "Fossil Galaxy".  M90's swift flight through the interstellar medium is thought to have stripped it of much of its star forming material via the process known as "Ram Pressure Stripping".  This appears to also have been compounded by several supernovae in its central arm regions, which would naturally be richer in this material.  The combined stellar winds from these events have blown much of the material out of the galactic disk and out of the gravitational influence of the galaxy.

M90 - Hubble Composite Image. Image Credit: NASA/ESA, Public Domain.

 
One and 1/3 degrees S of M90 lies another spiral galaxy, M58.  Although M58 is a little fainter than M90, at +9.69 mag, it appears, due to its compact size - 6.0 x 4.8 arc minutes - a little brighter overall.  M90 is a barred spiral, though due to the relative brightness of its spiral arms, the bar appears a little obscure, particularly in smaller telescopes - though these will show its disk shape well.  Larger instruments will start to resolve the mottled internal structure and arms better, with the central bar becoming more obvious in instruments of the 8-10-inch class.  M58, alongside M90 is a relatively poor galaxy for star formation and seems to be a victim of the dreaded Ram Pressure Stripping as well.  Lying some 62-68 million light years away (sources differ) it is suggested that at the time of its discovery by Messier in 1779, it was the furthest observed object in the Universe.

M58 - Copyright Adam Block Mount Lemmon SkyCenter University of Arizona, Creative Commons.

 
Just over a degree to the E of M58 lie the first of two elliptical galaxies, M59 and M60 (a little under half a degree further E).  These two galaxies were first discovered by Johann Gottfried Koehler in April 1779, Messier listing them shortly after.  Both men were principally concerned with comet watching rather than any notion of "Deep Sky" objects - ironically their discoveries of these pesky objects getting in the way of "true" comets would ultimately be of much greater cosmic significance.   

M60 and companion, NGC 4647 - Copyright Adam Block Mount Lemmon SkyCenter University of Arizona, Creative Commons.

 
Of the two galaxies, M60 is dominant, being +8.8 mag to M59's +9.6 and slightly larger at 7.6 x 6.2 to M59's 5.4 x 3.7 arc minute size.  Still, M59 in a large telescope is a fine object, displaying a bright outer halo, though M60 trumps it in imaging terms, which reveal a closely packed spiral companion galaxy, NGC 4647, at +11.30 mag, to its NW, overlapping the larger elliptical's outer regions.  It is possible to see this attendant galaxy with large telescopes (12-inch+) from a dark site, but it will be difficult with anything smaller.  It is debated whether or not NGC 4647 is truly interacting with M60, as evidence, bar the obvious visual closeness has been scant.  However, latest observation by the Hubble Space Telescope suggest that interaction is possibly at the beginning stages and the two objects are not simply line of sight co-incidental. 

 Both M59 and M60 are thought to contain supermassive black holes in the order of mass equal or larger than the mass of M87's - with M60's thought to be a huge 4.5 billion solar masses.

 

If we trace a line back West from M60, to M 59, then back to M58, we have a starting point for the identification of the next target for this month, the Siamese Twins Galaxy or Butterfly Galaxy.  This is in fact two objects, NGCs 4567 and 4568, which can be found just over half a degree to the SSW of M58.  These objects are +11.30 and +10.80 mag respectively and can be resolved as a V-shaped patch of light in smaller telescopes.  Larger (8-10-inch class) instruments will clearly resolve the objects as a much more rounded "V" - very reminiscent of a butterfly in flight, in fact.  Larger instruments under good conditions will start to resolve some variance of brightness within the disks, but it is in astrophotography that this target really begins to show its true awesome beauty.  Images reveal the early onset of a collision between these two spiral galaxies, which has been confirmed by professional infrared observations.  

 

NGCs 4567 and 4568. Hubble Image. Image Credit: NASA/ESA, Public Domain.

 
Following a line from M58, through the Siamese Twins, extending SSW by just over 3 and 1/2 degrees, we come to the penultimate object for discussion this month, the bright elliptical galaxy M49.  M49 was discovered by Messier on 19th February 1771 and was the first of the Virgo group to be added to his list of objects.  At +8.39 mag and 10.2 x 8.3 arc minutes dimensions, this galaxy is large, but still pretty bright - certainly conspicuous enough in binoculars under average conditions.  Indeed, M49 is the brightest of all the Virgo cluster, though M87 does give it a run for its money.  It was thought that both objects were of similar size and mass, but observations have now proved than M87 is by far the larger and heavier of the two galaxies.  By comparison, M49 has "only" 6000+ globular clusters to M87's 12000+.

M49. Image Credit: Ole Nielsen, Creative Commons.

 

Four degrees to the SSW of M49, extending the imaginary line we stared from M58, we come to the final objects in this month's epic tour of just some of Virgo's Deep Sky delights.  This object is one of the most beautiful and the most active, M61.  M61 was discovered by Barnabus Oriani on 5th May 1779 and was also noted on the same night by Messier, who classed it as a possible comet.  Less than a week later, Messier had realised that M61 was a static object, so then added it to his list.

M61, Hubble Image. Image Credit: NASA/ESA, Public Domain.

 
At +9.69 mag and 6.5 x 5.9 arc minutes, M61 is a fairly compact galaxy, having a bright star-like core, surrounded by evidence a its face on spiral nature, which is visible in smaller telescopes as a tenuous halo, but is resolved much more readily and successfully by the 12-inch+ class of telescope into a definitive spiral.  In fact, M61 is another barred spiral, but this bar is very compact in comparison to virtually every other barred spiral galaxy previously mentioned here.  Again, M61 is a worthy target for astrophotographers, who will pick up this compact spiral's structure well in long duration photographs.

 M61 is unusual in being one of the most active star-forming galaxies in the Virgo cluster.Likewise it holds the joint record with M83 as being the most active Messier object for Supernovae, with six being observed in the past century.

 

Text: Kerin Smith