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Telescope House March Sky Guide

 

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

 

We find ourselves at the annual crossroads that is March, with two significant events occurring that have wider ranging consequences for astronomical observations.  First of all, the Vernal Equinox, which occurs this year on the 20th March.  This is technically the halfway point between Winter and Summer and the time where the Sun crosses the celestial equator into the sky’s northern hemisphere.  After this point, very gradually, those in the northern hemisphere start to experience greater hours of daylight than night - though the geometry of our planet and it’s orbital tilt, means that these effects aren’t felt all over the world in exactly the same way.  More equatorial parts of the planet never experience as extreme differences in the shift hours of darkness or light at certain times of the year. However, for those of us at more extreme latitudes, the move of the Sun to the celestial northern hemisphere this has obvious repercussions: most significantly for those seeking true darkness to observe or image deep sky targets - the lack of which peaks at midsummer.   

 

The second event that has secondary repercussions for observations, is the annual changeover from standard time to daylight saving time, which occurs in Europe on 31st March this year, as a result of the equinox.  The old “Spring Forward/Fall Back” adage give you a clue which direction the shift is taking place.  This change is most often justified on the grounds of maximising working daylight hours, subsequent productivity and (arguably) to save energy.  This has the instantaneous  result of the sky being lighter at a later time of the evening for us in the northern hemisphere.

 

Of course, what works for the northern hemisphere has exactly the opposite effect in the southern hemisphere, who will be experiencing their Autumnal Equinox at the same time, which will precede the shift to standard time in some of these parts of the planet.

 

Wherever you find yourself, as ever, there’s plenty to see in the skies above us this March - so let’s see what lies in store for us…


 

 

The Solar System

 

 The Moon

 

The Moon begins March as a morning sky, presenting an Old Crescent phase of around 24% illumination.  It sits a little to the west of Saturn in the sky (by about 5 1/2 degrees).  The following morning, the Moon sits equidistant from both Saturn to the west and Venus in the east at sunrise.

 

On the 6th March, the Moon joins the Sun in Aquarius, becoming New.  This is the best time of the month for Deep Sky observation and astrophotography, as moonlight won’t affect viewing or images taken of fainter targets.  

 

Emerging on the western side of the Sun, the Moon will begin the climb into the evening sky.  This is the time of the year that a the New Crescent Moon begins to rise into a particularly steep part of the ecliptic for those based in the temperate northern hemisphere.  Although not strictly speaking springtime as yet, this month’s evening lunar phase is one of the “High Spring Crescents”, as the moon will reach quite some height in the sky while still at a relatively slim crescent phase.  The opposite will be the case in the Southern Hemisphere, as the moon will appear to rise in a very shallow part of the ecliptic.  This is a fabulous time for us northern hemisphere dwellers to observe and image the Moon in the evening, as greater separation from the horizon tends to bring better seeing conditions and the angle of the Sun to the Moon shows particularly striking lighting effects - especially within deeper craters and along mountain ranges, such as the Taurus Mountains, just a little above the Mare Crisium - and later towards the Moon’s half phase, when the more northerly Lunar Alps and the wonderful Montes Apennius and Caucasus ranges hove into view.  This part of the month also makes for favourable observations of the Mare Humboltainum on the extreme NE limb of the Moon.  This small, but distinctive sea is only visible when lunar libration allows us to see a little further over to the so-called “dark side” (which, as we all know, isn’t actually dark at all).

 

The Moon at sunset,10th March, showing Mare Humboltainum.  Image created with SkySafari 5 for Mac OS X, ©2010-2016 Simulation Curriculum Corp., skysafariastronomy.com.

 

The Moon reaches Half Waxing Phase on the 14th, while on the Taurus/Orion borders.  This Half Moon almost shares its billing as the most northerly in the ecliptic with next month’s, which will occur with the Moon in Gemini, at which point it will sit about half a degree further north in the sky.

 

The Moon reaches Full in Virgo on the morning of the 21st March. Naturally, the days surrounding this point of the month don’t represent the best time to observe and image deep sky objects - though meaningful imaging can be achieved with narrowband filtration.   This is the third “Supermoon” of 2019 - more accurately titled a “Perigee-Syzygy Moon”.  This occurs when the Moon is at a close approach to Earth on its slightly elongated orbit and while it can occur at any point on the Moon’s orbit around the Earth, the more popular term “Supermoon” is generally recognised as being when this closest approach occurs when the Moon is Full.  While there’s no massive significance of a “Supermoon”, tides can be affected and higher than usual as a result of close approach - though this is most prevalent when a Perigee-Syzygy lunar event occurs when the Moon is New and thus in line with the Sun.  At this time the Moon appears about 7% larger than the Moon at its smallest angular diameter, so it is actually quite difficult to notice the difference between a Moon which is “Super” or otherwise.  However, the term has captured the public’s imagination and anything that gets people looking at the sky and engaging a bit more with the science behind this is to be encouraged.  Suffice to say, Full Moon is quite a disappointing experience to observe through a telescope, as surface features tend to be bleached out by direct solar illumination - apart from those found on the extreme limb of the Moon's disk.  Due to this, earlier in March will be a much better time to look at the Moon in earnest, when incidental illumination reveals much more in the way of detail.

 

The Moon reaches Last Quarter in the constellation of Sagittarius and can be found positioned neatly halfway between Jupiter (to the west in Libra) and Saturn (in eastern Sagittarius) in the predawn sky. 

 

Our natural satellite ends March in Capricornus, as a 25 day old Waning Crescent. It rises in a very shallowly-rising part of the ecliptic from the northern hemisphere so won’t gain a tremendous height from the horizon before sunrise. 

 

 

Mercury

 

Early March finds Mercury an evening object, at +0.1 mag in Pisces.  Setting around an hour and a half after the Sun, there’s (as ever) a limited window to catch the illusive innermost planet, though separation form the horizon after sunset is just under 15 1/2 degrees (from 51 degrees N), which for Mercury is pretty healthy.

 

Mercury at sunset, 1st March.  Image created with SkySafari 5 for Mac OS X, ©2010-2016 Simulation Curriculum Corp., skysafariastronomy.com.

 

As ever, nothing stays the same for this particular target for long, as we fast forward to mid-month.  By this point, Mercury is at inferior conjunction (in between the Earth and the Sun) and thus unobservable with conventional equipment.  At this point, Mercury is only 92 million km from Earth (a reasonable mean average of its closest approach).  After this point, Mercury begins to draw away from the Sun on the western, “morning” side, though it will be a little while before its observable again.

 

By the end of March, Mercury has increased its separation form the Sun by a significant amount, but unlike the evening apparition earlier in the month, it is now sitting in a rather shallowly-rising part of the ecliptic - in Aquarius.  This means that while Mercury is just under 24 degrees from the Sun, it is only just over 5 degrees in elevation (from 51 degrees N) at sunrise.  This, coupled with a relatively narrow crescent phase of 23%, means the planet’s brightness is comparatively low, at +1 mag, which will make picking it out in the dawn sky a very tricky task from mid-northern latitudes (though those in the equatorial regions and southern hemisphere will fare a little better).

 

 

Venus

 

Venus begins March as a morning object on the Sagittarius-Capricornus borders.  Shining at a steady -4.1 mag, Venus’ 15.6 diameter disk is illuminated by 72.3%.  The planet stands about 11 degrees high at dawn (from 51 degrees N), having risen around an hour and 40minutes before.  Venus is separated from the Sun by just under 41 degrees and will be bright enough to be seen well into the morning sky (if you know where to look).  On the 2nd and the 3rd of March, the Old Crescent Moon draws alongside Venus, the two making a pretty pairing in the dawn sky.

 

Venus and Moon,just before sunrise, 3rd March.  Image created with SkySafari 5 for Mac OS X, ©2010-2016 Simulation Curriculum Corp., skysafariastronomy.com.

 

By mid-month, Venus fractionally to -4.0 mag as it is shrinking - pulling away from the Earth on its faster interior orbit. By this point in the month, although it has increased its phase to 76.5%, Venus’ disk has diminished in angular diameter to 14.3 arc seconds.

 

By the end of March, Venus is no fainter, but has decreased its size yet further to 13.2 arc seconds, displaying a phase of just over 80% illumination. Now having crossed over into the constellation of Aquarius, it is only around 7 1/2 degrees in elevation as the Sun rises (from 51 degrees N), so despite its brightness will be obscured by atmospherics from more northernly latitudes, though those in the Southern Hemisphere and the equatorial regions of the Earth will have a much better view.  For those of us in the northern hemisphere, we must bide our time - this time next year (March 2020), Venus will be in a spectacularly favourable area of the sky for us to observe as an evening object.

 

 

Mars

 

Mars is a rather poor +1.2 mag, 5.1 arc second diameter target in Aries at the beginning of the month - and the trend is rather depressingly downward as far as observational prospects are concerned.  Mars is now 256 million km away - contrast this figure with its most recent closest approach to Earth of just under 58 million km in July last year  when the planet appeared five times wider in angular diameter and its not hard to see why a body only 6679 km at its widest point now appears so much smaller.   

 

By mid-month, Mars will have reduced in size further and dropped in magnitude fractionally to +1.3 mag.  At the end of March Mars sits just under the Pleiades in Taurus, presenting a tiny 4.6 arc second diameter disk and shining at +1.4 mag - half a magnitude fainter than neighbouring Aldebaran, Alpha Taurii.  It’ll be interesting to compare the colour of the two, respectively, in the sky at this point.

 

 Mars inbetween the Pleiades and Hyades, 31st March.  Image created with SkySafari 5 for Mac OS X, ©2010-2016 Simulation Curriculum Corp., skysafariastronomy.com.

 

Jupiter

 

March 1st sees Jupiter rising around four hours before the Sun, in the non-Zodiacal constellation of Ophiuchus. At -2.0 mag, it’s quite a distinct target, but not especially well-placed for us in the northern hemisphere, due to the planet’s position in the southern part of the ecliptic.  At 36.2 arc seconds diameter, the King of the Planets is of a considerably greater angular size than any other planet in the sky - its nearest rival, Venus, although much brighter, appears physically about half the diameter at the present time.  Jupiter will reach a vertical altitude of just under 17 degrees as the Sun comes up and the 1st.  The trend as far as Jupiter is concerned is towards the larger and brighter as we draw steadily closer to the planet on our faster interior orbit.  However the distances between us and Jupiter are vast and these increases will only happen very gradually.

 

Jupiter trtiple transit (GRS, Io and Europa), sunrise 11th March.  Image created with SkySafari 5 for Mac OS X, ©2010-2016 Simulation Curriculum Corp., skysafariastronomy.com.

 

By mid-month, Jupiter is much the same: it has increased its angular size a little to 37.8 arc seconds diameter and its magnitude concurrently to -2.1 mag.  The planet will now sit at around 16 3/4 degrees high in the south at dawn.

 

By the end of the month, Jupiter has increased its brightness to -2.2 mag and increased its angular diameter to 39.8 arc seconds.  Rising a little after 2am, it transits just under 40 minutes before dawn , which means it is starting to gradually sink in the Western Hemisphere of the sky as the Sun comes up, when the planet can be found sitting at an altitude of just over 15 1/2 degrees (from 51 degrees N).

 

 

Saturn

 

Saturn begins March as a morning object, rising at just before 4am and shining steadily, if unspectacular +0.6 mag in brightness.  Now just over 63 degrees to the west of the Sun, Saturn stands about 12 1/2 degrees above the horizon (from 51 degrees N) as the Sun rises, a resident of Sagittarius.  On the 1st and 2nd, the Ringed Planet is flanked by the Old Crescent Moon, to the west and east, on respective mornings.  The area of sky Saturn is in can also be found in relation to the much brighter Venus, which sits just under 13 degrees to the east at the beginning of the month.

 

As the month progresses, Saturn continues to rise earlier and subsequently gain altitude at dawn - on the 15th standing a fraction under 14 degrees high in the south as the Sun comes up.

 

By the end of March, Saturn stands 16 1/2 degrees high in the south at sunrise.  While it hasn’t gained in brightness significantly, the planet’s apparent diameter has increased to 16.4 arc seconds, as opposed to 15.6 as it was at the beginning of March.  Saturn is now separated from the Sun by just under 80 1/2 degrees  - in comparison to the figured of 52 1/2 degrees on March 1st.  This has led to Saturn rising 50 minutes earlier on the 31st than it did on the 1st.

 

Saturn and major Moons, early morning, 31st March.  Image created with SkySafari 5 for Mac OS X, ©2010-2016 Simulation Curriculum Corp., skysafariastronomy.com.

 

Uranus and Neptune

 

Uranus is observable during the beginning of March, but represents a challenge to see much of at all.  The planet is a +5.9 mag, 3.4 arc second diameter target in Aries at the month’s beginning, but stands only 24 degrees high in the west (from 51 degrees N) at the beginning of astronomical twilight, so isn’t in the best position for meaningful observations.  At this point in Uranus’ evening cycle, its position in the sky means it’ll only be under exceptional seeing conditions that it’s worth seeking it out at all.  Uranus comes to Superior Conjunction at the end of next month, so as March progresses, the opportunities for observation become fewer and fewer.

 

Neptune is at Superior Conjunction on the 7th, behind the Sun, so won’t be observable until it re-emerges in the morning sky and increases its separation from the Sun somewhat.

 

 Uranus and Netune relative positions, early evening, 1st March.  Image created with SkySafari 5 for Mac OS X, ©2010-2016 Simulation Curriculum Corp., skysafariastronomy.com.

 

Comets

 

2018 Y1 (Iwamoto) passed 0.30 au from the Earth on February 12th and was readily observable in amateur telescopes from suitably dark locations.  This recently-discovered comet technically reached binocular level brightness in early/mid-February, but due to the comet’s diffuse nature, was a difficult spot for those with smaller instruments. The comet peaked in brightness at around mag 7, but this is rapidly fading now.  Iwamoto will be a resident of Auriga for much of March until appearing to make a massive “dog leg” turn not long after crossing the border into Perseus in early April.  The comet will then skew back into Auriga, before tuning outwards into Perseus again.  This is change in apparent direction caused not by the comet itself, but by our changing perspective here on Earth, in relation to the comet’s orbit.

 

 Comet Iwamoto path during March.  Image created with SkySafari 5 for Mac OS X, ©2010-2016 Simulation Curriculum Corp., skysafariastronomy.com.

 

 

Deep Sky Delights - Leo and Surroundings

 

Last month, we looked at the spectacular Gemini and the rather small and dim - though not disinteresting - constellation of Cancer and the large, rather barren Lynx, This month, we turn our attention to the striking Leo and beyond.  

 

Leo and surrounding constellations.  Image created with SkySafari 5 for Mac OS X, ©2010-2016 Simulation Curriculum Corp., skysafariastronomy.com.

 

There can be little doubt we are now in the part of the year known as "Galaxy Season", as this area of sky is littered with them.  Galaxy hunting is not solely the preserve of those with the supposedly prerequisite "Big Dobsonian”.  Although to see much in the way of detail in many of the objects mentioned this month, aperture will certainly help, a good deal of these can be seen with smaller telescopes and large binoculars from decent, dark observing sites.  However, patience and care will be needed to pick the faint glow of these fantastically distant objects from the background sky.  However, to discern structure in many of the galaxies we'll cover requires one of two things: a large telescope of at least 10-inches of aperture, or reliance on accurate, autoguided long-duration exposure astrophotography.  To appreciate the true beauty of these massive, yet seemingly delicate structures, you need one or the other - though their location and observation (yet again), will largely be down to sky conditions - with galaxies, the darker the better!  Careful, gentle filtration will help with galaxy observation from more light polluted environments, but narrowband filters like the OIII, H-Alpha and others will rarely help as much for galaxy observation as they do for nebulous objects (except when a galaxy has particular emission regions, peculiar to these wavelengths of light).  A good Skyglow or broader "Deep Sky" filter will help increase the contrast of an object against the background sky, without cutting off many of the useful wavelengths that the galaxy is transmitting on.  A galaxy's spectral output is much broader than typical nebulosity, so gentle filtration produces the best results.

 

The first object on the list for observation is one of the most difficult to see, but probably one of the simplest to locate and the closest, galaxy-wise - the Leo I galaxy.  Leo I sits a third of a degree north of Regulus, Alpha Leonis - the principle star of Leo (though some publications rate it as closer).  Leo I is an elliptical galaxy of reasonable angular size (12 x 8.5 arc minutes) and of photographic magnitude +11.15. Leo I is a one of its furthest satellite galaxies of our own Milky Way, lying just over 800,000 light years from us.  Leo I was first detected in the Palomar Sky Survey, taken with the observatory's 48-inch Schmidt Camera in 1950.  Leo I's visual magnitude is deemed to be around +9.8 mag, which should put it easily within the reach of amateur instruments.  However, Leo I's easy-to-find location is also its potential downfall from a visual perspective: it lies so close to Regulus that the neighbouring galaxy is almost drowned out by its glare.  There are reports of the galaxy being found in 10-12-inch class telescopes, but it is very likely that an observer would have to place Regulus just outside of the field of view, using appropriate magnification, in order to see our galaxy's most distant satellite at all.  Leo I will appear as a misty oval of light, with no great discernible structure even in large telescopes.The galaxy appears to have no attendant globular clusters and contains few stars of advanced metallicity, meaning the stellar population is comparatively young - probably little over twice the age of the Sun.  The galaxy is surrounded by a halo of attendant gas, which it may (or may not) have formed from.

Leo I and Regulus field guide (north is up).  Image created with SkySafari 5 for Mac OS X, ©2010-2016 Simulation Curriculum Corp., skysafariastronomy.com.


This unusual object will be a challenge, but if found, you will be witnessing the furthest reaches of our own galaxy's orbital sphere of influence and in all likelihood its youngest attendant.

 

Roughly nine degrees east of Leo I lie a spectacular grouping of galaxies: the Messier objects M95, 96 and 105 (and its attendant galaxies NGC 3371 and NGC 3373).  This group occupies a compact area of sky (about 3 x 1.5 degrees of sky) and can be found halfway on a line drawn between Regulus and Iota Leonis - one of the rear legs of Leo.  Of the three galaxies, the beautiful M95 is the most westerly.  M95 is a barred spiral galaxy, placed almost face-on from our perspective. M95 was discovered - along with the nearby M96 - in 1781, by Pierre Mechain.  Messier catalogued both objects less than a week after Mechain found them.  At +9.69 mag, M95 is a relatively easy, compact object at 7.4 x 5 arc minutes in dimension.  Lying 31 million light years away from us, it is the closest of its group by a million light years.  As M95 is a barred spiral, it is likely that most observers with decent-sized telescopes will see the galaxy's central core region as a slightly elongated object, surrounded by a fainter haze of its arms.  Long duration images of the system reveal its structure in all its glory - the two massive spiral arms shedding stars into further outlying feathered lesser arms.  If, as it has been suggested, our own galaxy is a barred spiral, it could look much akin to M95 to outside observers, though our galaxy may have more in the way of outlying spiral structure in its arms.

 

Next door to M95 by a mere two thirds of a degree is another lovely spiral, M96.  A similar angular size to its neighbour, it is slightly brighter at +9.3 mag.  In contrast to M95, M96 appears to be dustier, but has a more compact core.  It is often listed as a double barred spiral.  This double barring, along with the wide spread of its arms and the galaxy's dusty nature make its spiral structure less well-defined than its neighbour M95's.  Similar in angular size to M95, at 7.8 x 5.2 arc minutes, M96 appears as a more compact 3 x 5 arc minute object in a 10-12-inch-class telescope, its bright central core surrounded by a fainter ring of starlight which make up its arms.  The reason it also appears slightly brighter than M95 in some listings is that the galaxy is considerably foreshortened in comparison to its neighbour.  Some listings incline it as much as 53 degrees to our line of site, whereas M96 is also recorded as being at a less extreme 35 degrees!  Whichever listing is correct, M96 is a great target for visual and photographic observations.

 

M95 and M96.  Image credit: Mark Blundell

 

Just under a degree to the north of M96 sits the grouping of M105 and the nearby NGC 3371 and 3373.  Of the three, M105 is the dominant and brightest at +9.3 mag.  It is often described as the analogue of Elliptical galaxies - and as such is much studied.  M105 is a later addition to the Messier list (added by 20th Century Astronomer Helen Sawyer Hogg), though discovered in 1781 by Mechain, Charles Messier did not confirm its discovery at the time and it was left out of his original listing.  It's difficult to understand why Messier chose not to include M105, as it is prominent enough - a misty patch of light in small telescopes and a condensed glow, with a healthy-size core in larger instruments.  Elliptical galaxies, but their nature are not generally thought to be as beautiful or as characterful as their spiral counterparts, but this should not put observers off trying to locate M105.  Indeed, many Astronomers now consider Elliptical galaxies to be the ultimate evolution of galaxial structure after two spirals merge - the end result of the Milky Way's potential meeting with M31 may well result in a similar structure to M105.  A clue to M105's past is that it contains few areas of star formation and a reasonably elderly stellar population, suggesting it is a more advanced galaxy in terms of age.

 

M105 - Hubble Space Telescope Image.  Image credit: NASA/ESA, public domian.

 

The second Elliptical in this close trio, NGC 3371, 7 arc minutes to the NE of M105, is almost as conspicuous as its neighbour at +9.89 mag, but is presented to us at a much more oblique angle.  Appearing elongated, even in small telescopes, larger instruments can reveal a clear, bright core and the misty halo of NGC 3371’s outer regions.  So easy is it in comparison and proximity to M105, it is difficult to believe that it was overlooked by Mechain and Messier.  William Herschel discovered it in 1784.  Although listed as the catch-all description of an elliptical galaxy, the more precise description of NGC 3371 should be as a Lenticular.  The galaxy has revealed a central bar structure in long duration astrophotography and like M105 shows an older star population than the mean average.

 

NGC 3771, 3373 and M105 field guide (north is up).  Image created with SkySafari 5 for Mac OS X, ©2010-2016 Simulation Curriculum Corp., skysafariastronomy.com.

 

NGC 3373 is the most challenging of this trio to observe - whereas the two previously-mentioned ellipticals are bright and their structure obvious, NGC 3373 is a whole two magnitudes fainter than either at +11.89 mag and much more the visual preserve of larger telescopes.  NGC 3373 is a spiral galaxy and shows a much more blue, energetic cast in long duration images (maybe somewhat reminiscent of a mini M33).  This is largely due to its disassociation with the group - although close in angular proximity to M105 and NGC 3371, NGC 3371 actually lies round 64 million light years distance, roughly twice that of its neighbours and has no connection to them. Instruments of the 10-inch+ range will show it, though it will be a struggle to observe in less powerful scopes. It appears as a pale misty patch to the SE of NGC 3373 and little detail is to be expected in most telescopes, though those owning larger instruments have reported a certain textured "lumpiness" to its appearance in the eyepiece.

 

At low power (sub x40) it is possible to squeeze M96, M105 and NGC3371 in the same eyepiece, as it is also possible to do with M95 and M96 - though owners of low focal ratio reflectors should be advised that it is often inadvisable to attempt to use such low magnifications, lest the shadow of the secondary mirror interfere with the view!

 

Leaving this group of galaxies aside, we return to the aforementioned Iota Leonis and trace a line back up one of the rear "legs" of Leo, until we come across the +3.34 mag star Chertan or Theta Leonis (sometimes known as Chort or Coxa).  Tracing the line back to Iota Leonis, stop approximately halfway: here is location of the next group of galaxies, the M65 Triplet, more commonly known simply as the Leo Triplet.  This triplet contains the Messier objects M65 and 66 and the elongated NGC 3628.  All three objects are spiral structures, though unsurprisingly they present themselves to us in differing aspects.  

 

M65 and 66 were discovered by Charles Messier in 1780, though often misattributed to Mechain.  Of the two, M65 is slightly smaller and fainter at + 9.30 mag. It has a bright central bulge and pretty luminous arms.  Presented at a significant incline to our perspective, occupying an area of 9.8 x 2.9 arc minutes, M64 also features noticeable dusky lanes within its arms, though these may well be made more prominent by foreshortening.  M66, on the other hand, is a broader barred spiral, brighter than its neighbour at +8.9 mag and taking up more area in the sky at 9.1 x 4.1 arc minutes. M66's spiral arms are not as regular as M65's, which seems to suggest total interactions with neighbouring NGC 3628 in the past, as does a displaced cloud of hydrogen which has moved outwards from its arms and now sits, motionless, around its galactic halo.

 

M65, 66 and NGC 3628 - the Leo Triplet.  Image credit Mark Blundell.


NGC 3628 is the faintest of the three at +9.50 mag and the longest at 13.1 x 3.1 arc minutes in dimensions.  This is a fascinating spiral, which is presented edge on to us and is bisected through its centre by a long, dark dust lane.  This is difficult in smaller telescopes, but becomes extremely prominent in larger telescopes.  10-12-inches of aperture will show it well, but in a telescope of 14-16-inches of aperture it is unmistakable (in a similar way to NGC 891).  Discovered by William Herschel in 1784, NGC 3628 is pretty obvious in relation to its neighbours, so again, it is mysterious why it wasn't discovered earlier.  NGC 3628 has tidally interacted with M66 which has lead to a huge stream of stars breaking away in a a staggering 300,000 light year long trail.  This feature is only apparent in very long and well-processed astrophotographs, but is amongst the most spectacular and extreme pieces of evidence for gravitational interaction amongst galaxies in the sky.

 

All three galaxies can sit within the field of view of a low power eyepiece in a rich field instrument, but large binoculars will show them well as a triplet too.  Sadly, NGC 3628's dark lanes won't be revealed by binoculars, but the Leo Triplet is well worth your attention, regardless of whatever optical aid you deploy.

 

All the galaxies mentioned so far, bar the outlying NGC 3384 and (confusingly) the much more local Leo I, are all members of the extended Leo I group of galaxies.  For clarification, Leo I the galaxy and the Leo I group of galaxies are completely unrelated!  The next group of galaxies we shall come to belong to the Leo II population, an associated, but separate group.

 

Moving northwards from the M65 Triplet, we come to another compact triplet of galaxies, the spiral NGC 3632 and a close pairing of elliptical galaxies NGC 3607 and 3608.   2 1/2 degrees S from Zosma, Delta Leonis, (the base of the Lion's tale), the pairing of NGC 3607 (+ 9.89 mag) and NGC 3608 (+ 10.80 mag) can be found.  Separated by just 5 arc minutes, the pair are easily located in small instruments, though it is the brighter (4.6 x 4.0 arc minutes) 3607 that is the more conspicuous. NGC 3632 is to be found three quarters of a degree to the east of this pairing.  At+10.6 mag NGC 3632 was discovered by Herschel, again in 1784.  It is a lovely, if compact spiral and is also listed at number 40 on Patrick Moore's Caldwell Catalogue.  Although recorded as an 11th magnitude object, it appears brighter due to the concentration of this light over its compact 2.7 x 1.9 arc minute area.  Larger telescopes are needed to bring out any detail in its outlying spiral arms.

 

NGC 3607 - Hubble Space Telescope image.  Image credit: NASA/ESA, public domian.

 

Leo is awash with fainter galaxies and those with big scopes will have a task avoiding them, but for now we leave Leo and venture further south to take in a few deep sky delights in Sextans and the westerly half of the huge constellation of Hydra, the Watersnake.  

 

Sextans is a dim and uninspiring group of stars, but it does contain an easily-found galaxy.  Trace a line south down from Regulus in Leo through Alpha Sextans, until you draw parallel to Alphard, Alpha Hydrae.  Here, three degrees east of the +5 mag star Gamma Sextantis, you will find NGC 3115, otherwise known as the Spindle Galaxy.  A reasonably bright +8.89 mag, NGC 3115, is presented edge on to us here on Earth, making it quite a condensed object, the dimensions of which are 7 x 2.5 minutes of arc.  The Spindle is unusual in that it is a very smooth Lenticular galaxy - essentially a Spiral without any defined arms, just a disk.  It is postulated that NGC 3115 is an old structure, in which much in the way of star formation has now ceased.  Whatever its history, one thing is certain: it is a huge object, thought to be up to 8 times the size of our own galaxy.  NGC 3115 was discovered in 1787 by William Herschel during his great deep sky survey of the 1780s.  This galaxy can be fairly easily found in binoculars from a dark site.  Small telescopes will reveal its elongated nature and larger instruments will easily resolve its central bulge.  The galaxy shows a very little in the way of any dust lanes, even in detailed images, so unlike the similarly aspected NGC 3628, evidence of this should not be expected to be visible in any telescope.

 

NGC 3115 composite image (HST and Chandra).  Image credit: NASA/ESA, public domian.

 

Drifting south from NGC 3115, the +3 mag star Lambda Hydrae is to be found.  Sliding SE from Lambda, down the water snake's body, the next major star we come across is the +3.81 mag Mu Hydrae.  Just under 2 degrees to the south of Mu Hydrae is the lovely Ghost of Jupiter Planetary Nebula, otherwise known as NGC 3242.  This compact 0.7 x 0.6 arc minute nebula shines at +7.30 mag and is quite conspicuous, due to its compact size.  The Ghost of Jupiter is so-called as it resembles the planet Jupiter in average dimensions, though here is where the similarity with its namesake ends.  NGC 3242 is a distinctly blue colour, even in relatively modest instruments and its complex inner ring systems have led some observers to liken it to an eye, staring back at them through space.  Long duration photos reveal much more of the inner structure of this fascinating planetary, though much will be revealed to the observer by using relatively high magnification through telescopes.  Binoculars will show the Ghost of Jupiter clearly, but due to its small angular size it will appear as a small defocused star.  This object was again discovered by William Herschel in 1785.  The Ghost of Jupiter superficially resembles the famous Blinking Planetary (NGC 6826) in Cygnus and the Blue Snowball Nebula (NGC 7662) in Andromeda, though is slightly brighter and does not exhibit the "blinking" phenomenon anything like as much as either do.  As with most planetary nebulae, the Ghost of Jupiter takes OIII filtration particularly well, but should not be missed even if you are lacking this.

 

Ghost of Jupiter, Hubble Space Telescope image.  Image credit: NASA/ESA, public domian.

 

The final object in this month's epic trek through the early Spring skies is the most westerly: the bright open star cluster of M48, on Hydra's borders with Monoceros.  At +5.80 mag, M48 is visible to the naked eye from a decent location, containing over 50 stars brighter than +13 mag.  It is a great binocular object at half a degree across and contains tumbling chains of stars visible in telescopes of all sizes.  Opinion is divided as to who actually discovered M48.  Although listed as an original Messier object, Messier's cataloguing of its location is way off target (and actually resembles, in RA value at least, the cluster NGC 2548).  Caroline Herschel's "recovery" of M48 in 1783, is often given as the true discovery of what we now know as M48.  It is a mystery how Messier missed what is such an obvious object, or how he came to list what he called M48 so far out of position with any readily identifiable star cluster.  Regardless, M48 is an easy target and can be found with relative ease sweeping west of Alphard, Alpha Hydrae in modest-sized binoculars.

 

 M48.  Image credit: Ole Gunnar Neilsen, Creative Commons.

 

Text: Kerin Smith