Sky Guide for May
Monthly Sky Guide May 2018
For of us in the Northern Hemisphere, the hours of darkness are rapidly departing, in anticipation of later June's Summer Solstice. By late June, many observers in temperate northern latitudes will be experiencing permanent astronomical twilight. But never fear - there are still plenty of targets coverred 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 starts May in Scorpius, low in the southern ecliptic from a northern hemispherical perspective, at just past Full. Being so close to Full Moon, naturally, this is not the best time for deep sky observations, or imaging faint objects without significantly narrowband filtration.
The Moon reaches Last Quarter on the 8th, while residing in Capricornus, having scooted past the brightening Mars on the early morning of the 6th.
The Moon reaches New as it joins the Sun on the Aries/Taurus borders on the 15th, after which it becomes an evening target. The evening of the 17th, it may be possible to pick out the tiny sliver of the very slim Crescent Moon alongside Venus, just after sundown, with the two bodies separated by around 5 1/2 degrees.
The Moon is still rising through a rather steep part of the ecliptic from a temperate northern hemisphere perspective, gaining altitude night by night as it moves through the constellations of Gemini and Cancer until it reaches First Quarter high in Leo on the 22nd. This month's evening lunar cycle is still one of the "High Spring Crescents" for which this time of year is notable and provides excellent opportunities for observation and imaging from temperate northern climes - though the Moon will not sit quite as high in the sky as it has the previous couple of months for observation in these parts of the world. After this point in the year, the Sun has moved to a more northerly part of the ecliptic, so the Moon will rise in the evening sky in a much more shallow part of the sky from temperate northern climes - a sure sign the warmer, lighter part of the year is upon us here.
The Moon reaches Full early in the morning of the 30th and can be found alongside Jupiter in Libra the following evening. Again, as was the case in early May, this is not the ideal time for deep sky observations and imaging.
Mercury begins May just past greatest western elongation, separated from the Sun by just under 27 degrees - though is still a rather disappointing +0.4 mag, 7.8 arc second diameter target, showing a 46% phase. Sitting in Cetus, Mercury is low at sunrise from a northern temperate perspective - a little over 4 degrees high (from latitude 51 degrees N) - and thus a challenge to observe.
By mid-month, Mercury has shrunk to 6.2 arc seconds across, though has increased its brightness and phase to -0.2 mag and 68% illumination respectively. Although the planet is still desperately low in the sky in Pisces for temperate northern hemisphere observation. The planet now sits 22 degrees from the Sun.
By month's end, Mercury is much brighter at -1.6 mag, though has decreased its separation from the Sun to just 7 degrees. Standing around two degrees high at sunrise (from latitude 51 degrees N), the planet will be extremely difficult from temperate northern hemisphere locations, though those in the equatorial regions of Earth should still be able to observe it.
By the beginning of the month, Venus stands over 21 degrees high in the west at sundown, shining at -3.9 and presenting an 11.5 arc second diameter, 88% illuminated disk. Venus is separated from the Sun by just over 27 1/4 degrees - but is still some way from maximum solar elongation, which it will reach in mid-August. Crucially, however, for observers in the northern hemisphere, maximum eastern elongation of Venus will occur when the Sun is in a much more northerly part of the ecliptic. This will mean Venus standing under half the height above the horizon at sunset than it does now, when observed from the temperate northern hemisphere (those in the equatorial and southern regions of the planet will fare much better though). Now, up to mid-May, Venus will still be gaining altitude within the northern ecliptic, so this is the best time to observe our planetary neighbour from northern parts of the world.
By mid-May, Venus has brightened fractionally to -4.0 mag and is now 12.2 arc seconds across, while showing just under 85% illumination. On the 18th/19th May, Venus crosses 06hrs of Right Ascension in the sky - the point that intersects the most northern point in the ecliptic. It stands 22 1/2 degrees high at sunset (from latitude 51 degrees N). After this time, Venus begins to lose apparent altitude in the sky at sunset from a northern hemisphere perspective.
By the end of May, Venus can be found in Gemini, still -4.0 mag and 13 arc seconds angular diameter. The planet is presenting an 80% illumination, which will continue to diminish as it grows closer to Earth on its interior orbit. Venus stands 22 degrees high above the horizon in the west at sunset (from latitude 51 degrees N) on the 31st.
By the beginning of May, Mars found in Sagittarius at a brightness of -0.4 mag and displays an 11.1 arc second angular diameter. During the next couple of months in the run up to opposition in late July, we will see Mars transformed in angular size and concurrently, brightness, as we draw alongside this fascinating world. Mars has now passed through its most southerly point in the ecliptic and while still low in the sky from a northern hemisphere observer's point of view, gently begins to climb in the sky for observers in these parts of the world. Southern hemisphere observers and those in the equatorial regions of Earth will still have the superior views of Mars in terms of angular separation from the horizon, but those of us in the northern hemisphere will take any advantage we can at present, as the major planets are all very much southern celestial hemisphere occupants at this point. Mars stands just over 15 1/2 degrees high at sunrise on the 1st (from latitude 51 degrees N).
By mid-May, Mars has crossed the border into Capricornus and is now -0.7 mag and 12.8 arc seconds diameter. Standing just under 16 1/2 degrees high at daybreak (from latitude 51 degrees N), the Red Planet will be clearly brighter than any other star in its particular area of sky.
By the 31st, Mars has yet again increased its brightness significantly to -1.2 and is now 15.2 arc seconds across. It now sits just under 17 degrees high in the south as the Sun rises (from latitude 51 degrees N). Mars is now a serious target for observation in any telescope and will display continental-sized surface features in practically any telescope. The use of filters, particularly the #23A Light Red filter, will help isolate these darker parts of the Martian disk. An #82a Light Blue will also help Mars' polar caps stand out. This filter will definitely be of use as during this particular Martian apparition, Mars' smaller southern polar cap will be turned towards us. This is more difficult to spot than the larger northern cap, which was turned towards us in the first few months of 2018, and the adjacent Hellas basin, which often fills with mist and clouds, can often be mistaken for the southern polar cap. Observations at different frequencies bring certain features to the fore and make their identification easier and more precise.
Jovian opposition is upon us this month - and with it comes the opportunity to observe the solar system's largest planet at its best.
The 1st finds Jupiter in Libra at -2.5 mag, 44.7 arc seconds diameter and standing 22 1/2 degrees high (from 51 degrees N) at transit point, which it reaches at 1.33am (BST). Jupiter rises at 8.51pm in the 1st.
Opposition night is the 9th, when Jupiter attains its maximum brightness and angular size: -2.5 mag and 44.8 arc seconds respectively. The King of the Planets rises at just before 8.15pm (BST) and transits at 12.58am, when it will sit just under 22 1/3 degrees high in the sky (from 51 degrees N).
By mid-month, Jupiter remains at -2.5 mag and is 44.8 arc seconds in diameter. It is 22 3/4 degrees high at transit point, which it will reach at 12.31am (BST, from 51 degrees N).
The end of May finds Jupiter still at -2.5 mag and 44.1 arc seconds across. The planet will stand 23 1/4 degrees high as it transits, which will occur at 11.17am (BST, from 51 degrees N).
The start of April finds Saturn at +0.3 mag in Sagittarius where it is now 17.5 arc seconds in diameter. The planet now stands just over 16 degrees high at sunrise (from 51 degrees N), having transited around half an hour before.
Saturn is now rising at just after 1am and increases in size and brightness as it approaches next month's opposition.
Mid-month finds Saturn still at +0.3 mag, though it has increased angular size to 17.8 arc seconds. The planet now rises at just after midnight and transits at just after 4am.
By the end of May, Saturn has increased its brightness to +0.2 magnitude and is now just over 18 arc seconds across. The ringed planet now rises at a little before 11pm (BST) and transits in the south at 3am when it will be 16 1/3 degrees high (from 51 degrees N).
Uranus and Neptune
Neptune is steadily pulling away from the Sun in the morning sky in Aquarius, but rises about an hour and a half before sunrise (from 51 degrees N) on the 1st. Uranus is still much closer on the Sun and as such neither are particularly well placed for observation during the early part of the month.
By the end of May, Neptune is a little better placed for morning observation, now rising about 3 1/2 hours before sunrise. Uranus, separated from the Sun by 38 degrees and only reaching just over 13 degrees altitude (from 51 degrees N) at sunrise is still relatively poorly-placed for observation.
Comet PanSTARRS C/2016 M1, is the only reasonably bright comet to be relatively easy to observe during May. It continues its journey south through Aquila into Sagittarius during May, brightening as it goes. Although the predicted brightness of the comet is difficult to predict, it could be as high as the 7th magnitude, but is more likely to be hovering between the 8th and 9th magnitude as it heads Sunward. On the evenings of the 14th-17th, the comet will be found quite close (under 2 degrees) from the Little Gem Nebula and Barnard’s Galaxy (NGC6822), and will probably be around the same brightness as these two objects. This relatively close encounter will doubtlessly make for a good photo opportunity for those with the necessary equipment. On the morning of the 27th C/2016 M1 will pass under 1 1/2 degrees to the west of Pluto, though the 14th magnitude dwarf planet will be much fainter than the comet itself. On the morning of the 29th May, the comet will appear in line with Saturn and Mars in the sky. If you trace a line between the two planets in the sky with reasonable sized binoculars, or a telescope, for a dark location you should be able to detect the faint glow of the comet.
May 6th is the peak of a reliable shower, the Eta Aquariids. This shower can range from a zenith hourly rate of anything between 20 to 60 meteors, depending on the concentration of material from the shower’s parent comet, the famous 1/P Halley. The radiant of the shower, which sits just adjacent to the “Water Jar” feature of Aquarius, puts in an appearance in the very early morning and subsequently never rises particularly high in the sky from a northern hemisphere observer’s perspective, which limits the amount of meteors us “northerners” can see on a given night. The shower tends to be slightly better observed from the southern and equatorial reaches of the Earth, where the separation of the radiant form the horizon is larger. However, regardless of where in the world you find yourself, the perennial spoiler of a meteor watcher’s party - the Moon - will be sitting just to the NE of Mars on the nearby Sagittarius/Capricornus borders. At around 67% illumination, it will drown out all but the brightest of meteors, meaning that this year, the Eta Aquariids won’t be at their best.
Deep Sky Delights in Coma Berenices and The Bowl of Virgo
Last month we covered the constellations of Leo and Cancer - a pretty big area of sky, home to many galaxies. This month, galaxy season continues although our swathe of the heavens is rather more modest in size, 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 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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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 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).
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.
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.
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.
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.
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.
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.
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.
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.
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+.
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.
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↑ Back to top