Dominating the short, late-spring nights is Arcturus, the brightest star of the northern hemisphere sky and the sentinel of spring. It’s the brilliant leader of the constellation of Boötes, the Herdsman, or Bear Keeper, an area of the night sky that’s bereft of bright deep-sky objects, including no Messier-designated targets. Don’t you think then that it’s rather fitting that otherwise uninspiring Boötes has been handed the distinct honour of hosting Arcturus, as well as several superb double stars, including the beautifully formed and named Pulcherrima (Izar, epsilon Boötis). 

Arrive at Arcturus

Arcturus is a magnificent naked eye star, shining at magnitude –0.04 – one of just four stars that can boast a minus first-magnitude – and with an obvious and attractive reddish-orange hue that’s easy to appreciate from even light-polluted locations. Arcturus is outshone from UK skies only by scintillating Sirius, at magnitude –1.4. 

At around mid-May, Arcturus (alpha Boötis) culminates about halfway up the southern sky at 11pm BST. Boötes stands tall, spread out from seven to 55 degrees declination and covering around 20 degrees or so east to west at its widest point. Its brightest stars outline a huge, kite-like shape that spans 23 x 10 degrees, with Arcturus anchoring the ‘kite’. 

If you’re still unsure you’re looking in the right place, then you can follow the well-trodden route to Arcturus from Ursa Major’s famous and distinctive ‘Plough’ or ‘Big Dipper’ asterism, now lying high overhead. Simply follow the curve of the Plough’s handle down towards the horizon, neatly-termed ‘arc to Arcturus’ in some quarters, until you land on the bright reddish-orange star. 

Of course, amateurs astronomers see Arcturus as merely a point-source, though try looking at it through binoculars or a small telescope to intensify the experience.

Arcturus is a classic class-K red giant star, with a precisely defined surface temperature of 4,290 Celsius. It lies 36.7 light years away, close enough for astronomers to directly measure an apparent diameter of 0.0210 arcseconds, which, at its distance, equates physically to a diameter 26 times the size of the Sun, though Arcturus’ mass is similar.

Pull over for Pulcherrima

Boötes hosts a half-a-dozen or so fine double stars, but there’s no argument about which one is best; it’s the wonderfully-named, by F.G.W Struve, Pulcherrima, Latin for ‘most beautiful’, or ‘loveliest’, and more soberly known as Izar, or epsilon Boötis. Despite the epsilon designation, it’s actually the second-brightest star in Boötes, shining brightly at magnitude +2.6. Pulcherrima forms part of the ‘kite’ asterism as a magnitude +2.3 star around 10.5° north-east of Arcturus. 

Turn even a small telescope its way and and with high magnification and good seeing you’ll get a splendid view of one of the best colour-contrast doubles stars in the late-spring sky. A magnitude +2.7 class-K0 orange giant is separated from a magnitude +5.1 white class A2 main sequence dwarf by an easy-to-split 2.8”. The secondary has a bluish cast through the eyepiece.

Xi Boötis’ colours a joy

Xi Boötis is a second outstanding double star in the Herdsman; heading back to Arcturus, nudge your telescope 8° due east to land on this magnitude +4.5 star. A small telescopes shows very pretty colour-contrast, with the primary, which exhibits a degree of variability between magnitudes +4.52 to +4.67, showing off a lovely yellow-orange tint, while the magnitude +7 secondary glows orange-red. 

The pair orbit around their common centre of gravity once every 151 years in a highly-elliptical orbit. From Earth, their separation swings between 2.1” to 7.3”; having reached their widest separation in 1978, the stars are now slowly closing and will reach 2.1” separation in 2066.

Alkalurops: Another great moniker

In the more northerly regions of Boötes, close to its boundary with Corona Borealis, lies magnitude +4.3 mu 1 Bootis. It’s worth a visit solely for its marvellous proper name of Alkalurops, Greek for ‘club’. However, there’s more to it than just a great name as it’s a great triple star. 

At first glance at low powers the system appears to be just a wide double, owing to the yawning gap of 1.8’ between the  magnitude +4.6 yellow primary (Alkalurops) and the seventh-magnitude secondary mu 2 Boötis. However, ramp up the power on the latter through at least a 100mm (four-inch) telescope and it will split into a yellow-orange pair with a separation of 2.2”.

During late spring or early summer—whichever term you choose, likely depending on how fine the weather has been—is the best time to seek out and observe globular clusters, which are among the most striking and impressive categories of deep-sky objects.

Globular clusters are densely-packed, near spherical collections of ancient stars that populate mainly the extended outer halo of our galaxy. They are believed to have formed in the very early life of our Galaxy, over 11 billions years ago; Messier 3 is thought to be 11.4 billion years old.

Astounding star densities exist inside even run-of-the-mill globulars; on average, 0.4 stars per cubic parsec (a parsec is equal to 3.26 light years), rising to 100 to 1,000 in the denser core.

Messier 3 is one of the largest globular clusters known, with a physical diameter of at least 180 light years, though some sources raise that to 200–220 light years. One thing’s for sure, its tidal radius is a lot more, extending its sphere of gravitational influence by over three times. At its distance of around 34,000 light years, its imposing size gives it an impressive apparent diameter of 18 arcminutes.

Where to look

Messier 3 is located in the south-west corner of Canes Venatici (the Hunting Dogs), near to the boundary with Bootes and Coma Berenices. In early May, M3 is about 90 minutes from culmination as nightfalls, riding high in the southern sky at an altitude of around 60°. It can be observed throughout May’s relatively short nights, remaining on show until early September.

Shining at around magnitude +6.2 Messier 3 is an easy target for 10 x 50 binoculars; sweep for it about six to seven degrees east of magnitude +4.2 beta (β) Comae Berenices. It should appear clearly non-stellar as a fuzzy, unresolved patch of light.

How easy a globular cluster is to see is not solely down to its brightness; its degree of condensation (how densely packed it is) is also a critical factor. A dense, compact, star-rich globular will show a greater contrast with the background sky and therefore be easier to see than one that is diffuse, and tends to get lost in the sky background. Globular clusters are rated according to the Shapley-Sawyer 12-point scale, which indicates the degree of condensation. It ranges from I (very dense and compact) to XII (extremely diffuse with no central concentration). Messier 3 sits around midway on this scale as class VI, indicating medium density.

Through the eyepiece

Messier 3’s individual stars at its outer edges of its 19-arcminute form can start to be resolved through a 80–100mm (three- to four-inch) telescope at around 100<M>x<M>. A 200–250mm (eight- to ten-inch) telescope operating on a steadying transparent night can reveal countless stars across M3, mining those deep at its core at high magnification.

As an interesting aside, there are so many great globulars to choose from in May. Indeed, you could conduct your own globular Messier marathon if you’re so inclined, as all but one of the globular clusters listed in the Messier catalogue, Messier 79 in Lepus, is above the horizon at some stage on May nights.

Amidst the myriad spring galaxies lies NGC 4361, a large and bright planetary nebula located in the southern constellation of Corvus, the Crow. Locating it means dipping low towards the murkier skies close to the horizon, but it’s well worth the extra effort to find and observe it.

Corvus lies south of the ‘bowl’ of Virgo asterism.NGC 4361 forms the apex of an upside-down triangle with magnitude +2.9 Algorab (delta [d] Corvi) and magnitude +2.6 Gienah (gamma [g] Corvi), the northern pair of stars in Corvus’ irregular quadrilateral-shaped asterism of third-magnitude stars. It lies about 2.5° from both stars. NGC 4361 culminates at around 11.30pm BST at an elevation of just short of 20°. 

NGC 4361 appears clearly as a nebula through a 150mm (six-inch) telescope at a power of 50x, though a small telescope will struggle to show it as anything other than an ‘out-of-focus star’ at low power. Image show a delightful object, covering almost 2’ at its fullest.

As interesting as NGC 4361 is it’s not Corvus’ stand out object. This accolade falls on the remarkable Antennae galaxies, the colliding NGC 4038 and NGC 4038. The pair lie just over 5° west of NGC 4361, so it’ll be a waste if you miss out on trying to find and observe them. 

NGC 4038 and NGC 4039 are popularly called the Antennae for the streamers of stars, gas and dust stripped out from both galaxies as a result of their violent celestial encounter. They are located just to the west of the Corvus’ aforementioned asterism; sweep 3.5° south-west of Gienah (gamma [γ] Corvi, magnitude +2.6). Both are rather small and similarly-bright galaxies (magnitude +10.7, with NGC 4039 to the south slightly the larger, spanning 3.2’ x 2.2’ as opposed to 2.6’ x 1.8’ for NGC 4038. Owing to the Antennae’s low altitude from the UK, a 150mm (six-inch) telescope shows the pair as just a fuzzy halo about 2.5’ across.

Deep amateur images can show some of the turmoil and destruction that the encounter has unleashed, including the amazing ‘antennae’.

The Virgo Cluster of galaxies reigns supreme for galaxy enthusiasts on spring nights. Its teeming galaxy fields centred either side of the boundary between Virgo and Coma Berenices are crammed with any number of outstanding individual galaxy gems, but if you’re wanting more bang for your buck, then track down Markarian’s chain, a string of galaxies that includes Messier 84 and 86 and the interacting pair NGC 4435 and 4438, popularly called ‘The Eyes’.

Find the link 

Markarian’s Chain consists of a line of at least eight galaxies that curves north and east from Messier 84 and 86, just inside Virgo’s territory, and extends for about 1.5° to NGC 4477 across the boundary in Coma Berenices. All of the ‘chain gang’ should be within range of a 150mm (six-inch) telescope. In early April, the Chain is well up in the east-southeast by nightfall and goes on to culminate around 50° high at about 12.20am BST. 

Dominant at the western end of the chain are Messier 84 and 86, a pair of ninth-magnitude elliptical galaxies (classed as E1 and E3, respectively) lying around 17’ apart some 5° north-west of magnitude +5 rho (r) Virginis. As a challenge, if you are using a telescope in the 300mm (12-inch) class, shift your gaze slightly to the south of M84 and M86 and see if you can spot NGC 4387, a magnitude +13 galaxy that spans just 1.7’ x 1’.

The next two links in the chain, NGC 4435 and 4438 (also catalogued as Arp 120), the interacting ‘starburst’ pair known as ‘The Eyes’, are the most interesting. NGC 4435 is the smaller, more northerly galaxy of the pair, a barred lenticular that, shining at magnitude +10.8, is fainter than NGC 4438, its larger and much-disrupted neighbour (+10.0), though it exhibits a higher surface brightness.

Moving further north and east but staying in Virgo sees NGC 4461, a 3.7’ x 1.5’ eleventh-magnitude spiral, with NGC 4458, a smaller and round elliptical, just to the north. A 150mm (six-inch) telescope should show the former but you will probably need a 200mm (eight-inch) ‘scope for the latter.

The last links in the chain lie across the boundary in Coma Berenices. NGC 4473 is a magnitude +10.2 class E5 elliptical spanning 4.5’ x 2.6’ and, finally, lying around 12’ north is magnitude +10.4 NGC 4477, another spiral which covers 4’ x 3.5’. Both galaxies appear similar through a 150mm telescope.

In its 29.5-day voyage around Earth, the Moon makes its first observable appearance as a scimitar of light to the west of the Sun perhaps a day or so past new. Still in the Sun’s proximity, the thickening crescent remains accessible not long after sunset. However, as the Moon steadily puts more sky between itself and the Sun, it sets ever later into the twilight.

Increasingly taking charge of the evening sky, it becomes more obvious against a darkening backdrop as its phase advances towards first quarter. Afterwards circling further behind our planet, it makes its appearance ever later into the night as sunlight steadily consumes the Earth-facing surface until the maximum illumination of full Moon.

In the 14 or so days between new and full, the shadowed line between light and dark that we call the terminator passes through some of the Moon’smost fascinating features – some well-trammelled, others less so. I would like to take you on that journey, sampling just a few of those treats, looking through three visual windows: with the eye alone, through binoculars (by which I mean the ‘classical’ 7× to 10 × 50mm class) and with the aid of a small telescope of maybe 70- 80mm (~three-inch) aperture.

Catch a young Moon

Tracking down a young Moon early in its lunation is a popular observing adventure. On 9 April there’s a chance to see the Moon when it’s just over 24 hours old (1.02 days with a 1.37 per cent phase) following the new Moon of 8 April at 18:21 UT. At sunset from London and Edinburgh, at 7.50pm and 8.08pm BST, the Moon lies 11° high. 

Sweeping with a pair of binoculars or a small telescope AFTER sunset across an unobstructed western should snare the Moon. Let’s hope local atmospheric conditions are particularly fine, free from obscuring thin cloud and haze.

A day or so after new Moon: Earthshine

The Sun-illuminated phase presented to the Earth is the thinnest crescent – a mere glancing blow of sunlight. However, an observer on the Moon looking towards us would see the exact contrary. In the lunar sky, an almost full Earth would be a brilliant source of light. This light illuminates the rest of the Moon’s surface, making it dimly visible to terrestrial observers.

This ‘Earthshine’, or ’Earthlight’ caneasily make major features like the lunar mare visible to the unaided eye. Against a dark sky the effect is a wonder.Through binoculars, even some of the Moon’s lesser features are easily picked out viathis eerie light.

Three-day-old Moon: Buzzing the Pleiades, Polar horns and Mare Crisium

On the evening of 11 April the Moon lies around 3° above and to the left of the magnificent Pleiades open cluster (M45). At about 9pm BST the sky will have darkened sufficiently to make the scene very picturesque, especially with brilliant Jupiter lying below, though you’ll need a good western horizon to see it all.

By the time that the Moon is three daysold, it has adopted perhaps its mostclassical appearance, when the polarregions form extended talons (or horns)into the darkness. Illustrators will have owls, fairies and other fantastical creatures ‘sitting’ nonchalantly on the south polar ledge. Others will naively have the curve of this evening phase pointing the wrong way (not as it should, towards the unseenSun beneath the horizon) and might even have ‘foreground’ stars embedded against the Moon’s un-illuminated surface.

For naked-eye observers Earthshinemay still be easily seen, but so far asthesunlit Moonis concernedthe major feature to emerge since new is the MareCrisium (Sea of Crises). As a dark eye-likepatch of grey in the northern part of thecrescent it is unmistakable. Its oval shape is merely an effect of foreshortening since in reality it is an approximately circular impact basin 600 kilometres in diameter.

In addition to being a fascinating limb feature, Mare Crisium also serves as a useful indicator of lunar libration. Libration is an effect of the Moon’s elliptical orbit, by which we sometimes see‘around the corner’ of the face of the Moon turned towards us. We consequently sometimes see Mare Crisium appear well away from the visual edge of the Moon and other times hard up against it. Libration is avery useful phenomenon, by which the Moon offers us a view of 5percent of its surface, rather than just the 50 per cent one might expect from a ‘locked’ orbit. After new Moon, it is always fascinating to discover how far this time theMoon’s disc has ‘nodded’, one way or the other.

The rugged southern uplands

For binocular and telescopic observers another treat is available, for which we must descend to the very southern tip of the crescent.

The south pole of the lunar surface offers some of the highest and roughest terrain on the Moon. At the sharp end of the Moon’s southern horn the local sunrise is now grazing the very tips of this chaotic region. The result is a steadily diminishing chain of illuminated mountain tops divided by chasms of inky blackness. The effect is dramatic in binoculars, but a telescopic view will reveal an almost star-like procession of incandescent points trailing away into nothingness. It is often great sport to see how far into the razor’sedge you can resolve those sunlit rocky crests.

Lunar day five: Craters Theophilus, Cyrillus and Catharina

With the dawning of lunar day five, the ever-moving terminator throws into deep relief one of the best crater chains that the Moon has to offer – that of Theophilus, Cyrillus and Catharina. Located in the mid- southern latitudes, these three features, all approximately 100 kilometres across, command the area at this time. If the observation opportunity is just right, the early lunar morning crater ramparts will sufficiently project into the Moon’s dark hemisphere to make the terminator look jagged to the naked eye alone.

For binoculars, this trio of deep impacts is very rewarding, standing out crisplya gainst the much darker volcanic plain of Mare Nectaris (Sea of Nectar) to the right.Telescopically, the northernmost of this group, Theophilus, provides one of the best examples of a crater’s major features; its entral peak is a multiple summit1, 400 metres high, with the crater walls showing massive slumps and landslides.

Seven days in: First Quarter phase reveals trio of Maria

Seven days after new Moon, we reach the first cardinal point of the Moon’s orbit, when (at 90° to the Sun) a precisely vertical terminator line cleaves the Moon exactly in two. By this time, the unaided observer will notice that a bold diagonal line of three contiguous Mare have joined Crisium in the Moon’s western hemisphere, running roughly from the terminator’s mid-northern latitude to the equatorial limb.

Beginning with the topmost, these are the Mare of Serenitatis (Serenity), Tranquillitatis (Tranquillity) and Fecunditatis (Fertility). Tranquillity was of course the site of anything but, when humans made their first lunar landing there 55 years ago.

In the northern hemisphere, a ragged curved feature now appears a massive chain of mountains called Montes Apenninus, the lunar Appenines. They form the south-western ramparts of the Mare Imbrium (Sea of Showers) – a massive flooded crater plain 1,250 kilometres across only partially revealed at this phase. These mountains are essentially what remains of Imbrium’s crater wall. The seven-to-eight-day-old Moon will throw this ideal binocular feature into deep relief.

Day eight dawns: a lunar lady unfolds

By day eight the Moon is really getting into its stride. Its phase, now greater than 50 per cent, is termed gibbous (from a Latin term indicating ‘humped’).

At this time, the naked-eye observer gets an anthropomorphic treat, for a young lady appears. For myself, I perceive her as a late Victorian woman, with the three contiguous Mare of the north- western hemisphere forming her piled hair. The dark patch of Mare Vaporum (Sea of Vapours) beneath Serenity forms the eye and beneath that a cleft created by Sinus Medii (Middle Bay) mimics a mouth. She appears to be gazing wistfully towards the Moon’s top left quadrant.

If you catch the lunar lady rather late on day eight, the creeping terminator may have moved sufficiently eastwards to adorn her slender neck with a sparkling jewel – this being the intensely bright crater Tycho. It may qualify as the easiest crater to be visible to the naked eye.

Tycho, a wall and colossal craters

This is a great time to look at Tycho with binoculars. It is a deep, crisp excavation 86 kilometres in diameter with an impressive central peak. Relative to the rest of the Moon it is young, perhaps only 100 million years old – though it looks like the impact occurred only yesterday. Streaking away from it, curving upwards towards the north-western limb, faint brushstrokes of light can be seen. But more on these later.

Scanning slowly northwards up the terminator, just halfway towards the lunar equator, a telescope will show something entirely incongruous amongst the dominant circularity of crater formations – a straight line. This is no unearthly signature of an ancient alien civilisation, but rather it is a slump in the lunar crust – a linear fault 110 kilometres long known as Rupus Recta (Straight Wall).

This huge escarpment looks like a cliff face, but is in reality a slope sufficiently shallow to be scaled by walking! Its appearance is actually quite transitory and within another day or so its local Sun climbs above the slope and the shadow vanishes. It can thereafter only be seen with difficulty as a faint line.

Close by the Straight Wall, a little farther up and to the right, we chance upon a second prominent trio of colossal craters: Ptolemaeus, Alphonsus and Arzachel (with diameters of 154km, 118km and 98km, respectively). They are easily visible in binoculars and like their predecessors a couple of days prior, these impacts are classics of crater formation, although appearing rather more worn with floors heavily smoothed by upwelled lava.

A small telescope will show that of the three Arzachel does present evidence of craggy terracing within its walls and a rather tame central peak.

The full 1,000 kilometre extent of the lunar Appenines can now be seen in binoculars. If telescopic observers follow this range’s southern tip into the terminator, they will find a deeply

punctured 60 kilometre-diameter crater called Eratosthenes. Its internal walls are heavily terraced and the prominent central peak stands very tall at the centre.

Should the local Sun still be low, this central peak may be visible as a star-like spark against the unlit crater floor. If conditions are very good and your ‘scope will allow higher magnification, the crater floor will be seen as not smooth, as is the case with so many, but strewn with rubble.

Lunar days 10: Mighty Copernicus rules

Day 10 sees much of the Moon’s eastern hemisphere coming into view. The majority of the Imbrium basin is now in sunlight. Together with Mare Insularum (Sea of Islands), Cognitum (the Known Sea) and Nubium (Sea of Clouds) beneath, it now forms a contiguous dark laval region running almost the full length of the terminator. Like a long shadow, this is easily noticed without optical aid.

Slap bang in the middle of this otherwise featureless band of Mare is the vivid splat of Copernicus, a monstrous impact crater nearly 100 kilometres across. Binoculars will reveal the massive spray of ejecta surrounding it, the bright residue starkly seen against the heavy grey of the surrounding lava plain. Drawing closer with a telescope will reward the observer with deeply terraced crater walls and a jumble of central mountains.

Lunar day 12: the Aristarchus Plateau

The dawning of lunar day 12 sees the bulk of the last major ‘sea’ to emerge blinking into the sunlight, Oceanus Procellarum (Ocean of Storms). It inaugurates the appearance of two of my favourite areas of the telescopic Moon, the Aristarchus Plateau and the Marius Hills.

Like Copernicus, Aristarchus is another very bright crater (albeit a little smaller at 40 kilometres in diameter) struck lonely into the gloomy barren backdrop of this stormy ocean. Indeed, some say it has the brightest reflectance of any lunar feature. Slightly higher and nearer the terminator than Copernicus, with Tycho these three bright craters comprise those most likely to be spotted unaided by those with acute vision.

A comparatively fresh impact, a telescope may reveal Aristarchus’ best known characteristic, the enigmatic vertical banding that at this time is visible against its deep multi-level internal terracing. The contrast of these mysterious scree slopes changes gradually with the Sun’s elevation. There are other craters that show a similar phenomenon, but it is in Aristarchus that it is most pronounced.

Observers using binoculars will enjoy a view of Vallis Schröteri (Schröter’s Valley), a snaking lava channel cut deep into the surrounding surface that emerges between Aristarchus and its neighbour, Herodotus. 

Below Aristarchus, about the same distance from the terminator, we alight upon dark-floored crater Marius. The area immediately to the west, between the crater and the terminator, is a raised plateau containing one of the Moon’s highest concentrations of volcanic activity, the Marius Hills. If timed correctly, long shadows will be cast by a series of domes, volcanic features averaging ½km in height and ranging in size between house-sized cones to mounds a few kilometres across. I will admit that this may be a challenging observation for a small telescope (possibly requiring at least an 80mm [three-inch] APO refractor), but even with lower resolution the area will look mottled.

Full Moon after a fortnight: The Man in the Moon

During day 14, the terminator completes its 10 m.p.h. (equatorial) crawl across the surface and disappears (around the corner of the eastern limb). The silvery gaze of the full Moon has arrived. As with the early crescent, poetic license is upon us once again, for the Lady of the Moon is now joined by her gender counterpart.

Familiar to most naked-eye observers, the Man in the Moon’s features arise from Imbrium being the left eye, Serenity being the right, Vaporum the shadow beneath his nose with Humorum and Nubium joining forces as the mouth. I have always thought his turned down grimace and the streak of tearful sadness (formed by Tranquillitatis and Fecunditatis) flowing away from his right eye make him look a little morose.

But we may be cheered by the full Moon’s other inhabitant, the rabbit. This takes a bit more effort to see – and very much depends on the Moon’s orientation with respect to the horizon, but here goes. Serenity is the rabbit’s snout, with Tranquillity, Fecundity and Nectar forming the back of its head and floppy ears. Imbrium constitutes its chest, with the darker areas below, the hind legs and feet.

Glorious lunar rays

In binoculars the full Moon provides one of astronomy’s most undervalued glories, the lunar rays. In those distant days when the lunar surface was being pummelled by incoming debris, each crater impact sprayed out vast clouds of tiny molten globules which froze before falling back to the surface as billions of perfectly spherical glassy beads. This misty ejecta was unevenly funnelled through the ragged terrain of the impact, so once settled, it created surface tracks of material that can be traced back to its origin.

At full Moon, with the Sun behind the observer’s shoulder (and the Earth!) these glass beads are serving as perfect reflectors, bouncing fierce solar light straight back towards the Earthly observer. This effect is so marked that the intensity of the rays can change quite markedly in the hours either side of full Moon, reaching their peak brightness as the phase angle reaches 100-per cent. So do not dismiss the rays as they portray the violence of the Moon’s history just as vividly as the craters they spawned from.

Get yer ‘scope out at full Moon

Don’t give up on the telescope either. Using a neutral density filter (and experimenting, as always, with others), a higher-power view of these ejecta blankets can be fascinating – and I think, brings home the violence of the original impacts like nothing else. With adequate filtration and favourable observing conditions, some of the lunar rays (particularly those originating at Tycho) can be traced all the way across the Moon’s face.

As soon as the terminator disappears from the Moon’s eastern flank, it makes its appearance in the west – but instead, begins to steadily extinguish the Moon’s surface rather than illuminating it.

I have spotlighted just a little of the Moon’s bounty. I hope it has whetted your appetite for continued exploration. Never forget that with ever-changing angles of solar illumination, the chances of an observer seeing features on the Moon in exactly the same light twice are vanishingly remote. Good hunting.

Sniff out the Hunting Dogs (Canes Venatici), the home of the magnificent Whirlpool Galaxy (M51) in the far northern sky, and you’ll find more galaxies than you can shake a stick at. Prominent Messier 106 (NGC 4258) is a superb spiral galaxy that holds its own in the company of the likes of the Sunflower Galaxy (M63) and M94. It’s bright enough to be found through a pair of binoculars and it looks like a galaxy through even a small telescope.   

Where to look

Messier 106 is located in the north-western corner of Canes Venatici; sweep with a pair of 10 x 50 binoculars 1.7° south of the star 3 Canum Venaticorum (magnitude +5.2) and on a fine night you should spot a faint smudge of light. M106 is circumpolar (never setting) from UK shores, culminating late-month almost at the zenith at about midnight GMT.

An 80mm telescope (three-inch) can show its elongated disc, orientated south-east to north-west, while upgrading to a 150mm (six-inch) reveals a slightly mottled, oval-shaped core extending to perhaps 10’ x 7’, with a well-defined nucleus surrounded by a faint outer halo of nebulosity.

A big galaxy

Messier 106 is a large galaxy comparable in size with the Andromeda Galaxy (M31), and has somewhat of a resemblance to it. Its physical diameter of 135,000 light years at its neighbouring distance of 24 million light years give it a large apparent diameter on the sky of 18’ x 7.9’. M106 is a strong source of radio waves from its an active core, giving it a Seyfert II classification.

Amateurs now routinely capture superb images of M106 and widefield data can show a number of much smaller galaxies, including NGC 4217, an attractive edge-on spiral with a notable dust line that’s visible through a 200mm (eight-inch) telescope, and, closer in to M106, NGC 4248, a smaller still irregular that can be picked up through a 300mm (12-inch) ‘scope. 

The Imbrium Basin is the largest impact basin on the Moon’s near side, with a diameter of around 1,160 kilometres. The South Pole-Aitken Basin on the far side is twice as large. The massive impact event that formed Imbrium, one of the most violent in the history of the Solar System that occurred 3.85 billion years ago, left a giant crater which was subsequently infilled by basaltic lava. 

Mare Imbrium (Sea of Rains), the huge lava plain that we see today in the Moon’s north-western quadrant, is the most obvious legacy of that ancient, cataclysmic event. Second only in size to neighbouring Oceanus Procellarum (Ocean of Storms), Mare Imbrium is obvious to the naked eye on a 10 day-old gibbous Moon; indeed, Imbrium forms the left eye of the famous ‘Man in the Moon’ feature. Raise a pair of binoculars or train a small telescope on Imbrium and it shouldn’t take long to realise that Mare Imbrium is bordered by a number of very impressive mountain ranges. 

Montes Apenninus

The most striking range is Montes Apenninus (the lunar Apennines), which majestically guard the south-eastern shore of Mare Imbrium. They sweep in a 600-kilometres arc from Promontorium Fresnel in the north to the peaks east of crater Eratosthenes. Montes Apenninus’ highest peaks include the impressive Mons Huygens (5,500 metres), the highest peak on the Moon, and Mons Hadley (4,600 metres), lying close to its eastern extremities. A 150–200m (six- to eight-inch) telescope, operating at a power of around 150× to 200×, zooms in nicely on Mons Huygens and just to its west Mons Ampère (3,000 metres). 

Montes Caucasus, Carpatus and Alpes

Montes Caucasus, to the east of Mare Imbrium, form a continuation of Montes Apenninus to the north-east (as far as crater Eudoxus). A third major range is Montes Carpatus (Carpathian Mountains), found just north of the mighty Copernicus impact crater, that mark the southern border of Imbrium. Together, Apenninus, Caucasus and Carpatus form the outermost of Imbrium’s three concentric rings of mountains, part of what is left of the rim of the basin following the lava flooding.

Montes Alpes (the Alpes Mountains), in the northeastern portion of the Imbrium Basin, is another famous feature that’s easily located as a rugged 250-kilometre-long south-east arc sweeping from the dark-floored crater Plato to crater Cassini. Look out for the striking Vallis Alpes, a rift valley that cuts right through the Alpine range 

Through binoculars it’s easy to see that at its southern extremities Montes Alpes lies just inside the western flanks of Montes Caucasus. This is because Montes Alpes was part of middle ring of the Imbrium basin.        

The Straight Range: part of an inner ring

You’re no doubt familiar with the Straight Wall (Rupes Recta), the 110-kilometre-long linear fault in the south-eastern part of Mare Nubian. How about Montes Recti, the Straight Range? It is an east-west orientated rectangular formation of peaks, around 90 kilometres in length and just 20 kilometres wide. 

Individual peaks and groups of peaks, including Montes Recti, are common close to the north shore of Mare Imbrium. Lying just to the east of Montes Recti is the better known range Montes Teneriffe and to the south of Plato is the isolated peak Mons Pico, which towers 2,400 metres or so above the plain. Close by to the south-east is Mons Piton (2,300 metres), another stand-alone massif. However, they only seem to be individual peaks as they are easily-observable traces of an inner ring some 790 kilometres in diameter, parts of the inner terracing of the basin that were high enough not to be drowned by lava that formed the mare surface. 

Further inspection southwards reveal more evidence of the inner-ring; Montes Spitzbergen (Spitzbergen Mountains) is located about 80 kilometres north of impact crater Archimedes. 

The west to north-western section of the Imbrium Basin lack anything like as substantial a mountain range, but the vast semicircular scarp of Montes Jura, bordering Sinus Iridum (Bay of Rainbows) indented in the north-western edge of Mare Imbrium, is a magnificent sight. 

Imbrium impact: craters

There are a handful of outstanding craters seen in the encircling mountains and standing in splendid isolation on the Imbrium plain.

The flooded crater Archimedes (81km) is the best and most prominent impact crater seen on the floor of the Mare Imbrium, at its eastern edge. Together with close companions Aristillus (55km) and Autolycus (39km), lying east and north-east, respectively, the trio provide a great sight. Looking through a small telescope, Archimedes has a smooth, Plato-like dark floor, which contrasts nicely with the marvellous central peaks of Aristillus. 

Cassini is a curious crater lying to the north-east of Aristillus. Like Archimedes it’s a flooded crater, but it’s floor contains the interior craters Cassini A and Cassini B, the former having an unusual floor. Archimedes and companions and Cassini are all on show on the morning of 17 October.

Crater Eratosthenes (60km)lies in the foothills of south-western Montes Apenninus (Apennines). It hasasharprimwithwideinternallyterracedwallsandahillyfloor,abovewhichrisesagroupof mountains. Many observers liken it to a mini-Copernicus. Before you finish observing Imbrium, be sure to take a look at dark-floored Plato, lying at the western end of Montes Alpes. 

Ghosts and crater chains: Take on challenges in Imbrium

Crater Lambert (30km) lies in glorious isolation on the Imbrium plane, around 350 kilometres west of Archimedes. Lambert is an easy target for any telescope but can you spot larger Lambert R (Ruin; 56km) lying just to the south? It is one of the Moon’s many ‘ghost’ craters. Astronomers believe it is an impact crater that was subsequently flooded by massive lava flows, left behind its rim as evidence of its former existence. 

Now head to Imbrium’s far south-eastern quadrant, around 100 kilometres north-east of crater Eratosthenes, to track down a little ghost crater called Wallace (26km). Both craters are much easier to spot when they are illuminated by a low Sun.

Multiple impacts

Who can forget when in 1994 over 20 fragments of Comet Shoemaker–Levy 9 – dubbed ‘string of pearls’ – slammed into Jupiter’s cloud-tops, producing a series of dark scars on the planet’s southern hemisphere, the largest of which persisted for months. The comet was torn apart by Jupiter’s overwhelming tidal forces  Astronomers believe similar impacts have occurred on the Moon and, unlike Jupiter’s long-dispersed scaring, we can observe the results. Perhaps the most famous of such features on the Moon is Cantena Davy, lying between crater Davy and majestic Ptolemaeus. However, there are a couple of them worthy of attention in the Imbrium Basin.

Cantena Beer

The small impact crater Beer (10km) lies around 115 kilometres south-west of the large crater Archimedes (80km). Astronomers think multiple impacts from a single, disrupted body, a comet or an asteroid, formed the chain of tiny craters (Cantena Beer; the largest crater is about 1.5 kilometres in diameter) seen arcing eastwards from Beer, eventually turning into a straight rille. You’ll need a telescope on the 250mm (10-inch) class to spot them, though Beer itself is an easy capture.

Crater Timocharis (34km) lies about 90 kilometres south-east of Beer. Lying just south-west of Timocharis are two much smaller craters, Heinrich (6km), the larger of the pair, with Timoocharis-C due east. Running north-north-eastwards from Timocharis-C is Cantena Timocharis, a 20-kilometre-long string of diminutive craters. This feature is probably best left to high-resolution imagers, though a large Dobsonian on a steady night could be successful. Try for Cantenae Beer and Timocharis on the morning

Early spring heralds the rise of the galaxies, when over the next three months or so the prime-time night sky is overflowing with a veritable treasure trove of bright and beautiful targets. Leo, the Lion, lies at the vanguard of this spring onslaught, offering as it does five Messier-designated galaxies and a handful of others that would wear the mantle comfortably.

Messier 95 and 96 are a very special pairing of photogenic spiral galaxies lying under a degree apart at the centre of Leo, about nine degrees east of Leo’s dominant star, magnitude +1.4 Regulus (alpha [α] Leonis). A small telescope will show the pair, while imagers can get great results, with wide-field shots having the substantial bonus of including Messier 105, a large and bright elliptical galaxy, in the field.

Track them down

At mid-March from London, Leo reaches the southern meridian at around 10pm GMT, with the M95/96 pairing culminating at around 11pm at a favourable 50-degree attitude. The pair can be comfortably observed for three hours or so either side of culmination; sweep for them with a small telescope some 4.5 degrees north-east of magnitude +3.9 rho (ρ) Leonis. M96 is the more easterly lying of the pair (M105 sits under a degree north-north-west of it), with M95 located 42 arcseconds west-south-west of its companion.

Similar numbers

They are remarkably similar in size and brightness, with Messier 96 (NGC 3368) being marginally the brighter than Messier 95 (NGC 3351), shining half a magnitude brighter at magnitude +9.2. M95 is slightly larger, with an apparent diameter of 7.4’ x 5.1’ as opposed to M96’s 7.1’ x 5.1’.

M96 is a spiral galaxy (morphology class SAB(rs)ab) with, in common with the vast majority of spiral galaxies, an elusive structure through a small telescope. It appears as circular diffuse patch of light through an 80mm (~three-inch) telescope at 40<M>x<M> power, while a 150mm (six-inch) reveals its core to be much brighter than the surrounding halo.

M95 sports a central bar (class SB(r)b) and is a superb-looking galaxy in deep amateur images. It’s appears diffuse than its companion through a small telescope, while an 80mm aperture can show a three-arcminute-wide glow, a tad larger than M96 offers. A 250-300mm (ten- to twelve-inch) telescope can reveal hints of M95’s bar under good conditions.

This time of the year is open cluster season for sure, with a whole host of prime examples of the species to choose from. Why not head in the direction of the under-observed southern constellation of Puppis to observe Messier 46 (NGC 2437), Messier 47 (NGC 2422) and Messier 93 (NGC 2447), a superb trio of clusters. 

M46 and M47 lie under 1.5° apart in a sparkling, star-studded winter Milky Way field, and are great objects to view together through a pair of 10 x 50 binoculars. There’s an added bonus too: peering through a moderate- to large-aperture telescope will reveal tenth-magnitude NGC 2438, a tiny planetary nebula that’s embedded within M46’s swarming stars. M93 lies nearly 20° south and with a declination of 23° south, can prove a challenging target from mid-northern latitudes.

M46 and M47

Puppis’ northern region is reasonably well seen from UK shores; if you can see Sirius (alpha [α] Canis Majoris), then M46 and M47, located around 13° east of the brightest star in the sky, are accessible to you. Along with Carina and Vela, Puppis formed part of the huge constellation Argo Navis, specifically the stern, or poop of the ship of the Argonauts, until that unwieldy beast was split up by Nicolas Louis de Lacaille, in 1763.

Messier 47, the more westerly-lying cluster, shines with an integrated magnitude of +4.4, making it the brighter of the pair. A small telescope shows around 30 stars among half a dozen or so brighter members, with many more becoming visible through a 250mm (10-inch) aperture. M47 spans around a full-Moon-sized half a degree. M47 has a dozen or so bright members which give impact visually.

The rich seventh-magnitude open cluster NGC 2423 lies just over half a degree north-northeast of M47. Images show the cluster is less spherical overall than its Messier neighbours, with an extension to the north-east which rather blends into the rich Milky Way background.

Messier 46, which lies just 1.3° to the east-south-east of M47, its close neighbour on the sky, sports a similar apparent diameter but shines significantly fainter, having an integrated magnitude of +6.1. It lacks the immediate impact of M47’s brighter members, but makes up for that by being richer in fainter stars, giving it the appearance of a very loose globular cluster. A telescope of 100- to 150mm (four- to six-inches) aperture can reveal over 100 stars on a transparent and moonless night at a dark-sky location.

M46 and M47 are not close neighbours in space; at a distance of around 4,500 light years, M46 lies two to three time farther away than M47.

In late-February, Messier 46 and 47 cross the southern meridian from London at around 9pm GMT, culminating not far short of 25 degrees in altitude. In addition to Sirius, alpha Monocerotis is a handy, magnitude +3.9 guide star which lies 5.3 degrees due north of Messier 46.

Go low for M93

Messier 93 is a very rich cluster of stellar jewels, picturesquely set in Puppis’ crowded winter Milky Way star fields, with magnitude +3.3 xi (x) Puppis lying just 1.5 Messier 93 is a very rich cluster of stellar jewels, picturesquely set in Puppis’ crowded winter Milky Way star fields, with magnitude +3.3 xi (x) Puppis lying just 1.5° to the south-east. Sirius lies 15° to the north-west.

M93 has around 80 stars that are confirmed cluster members spread over around 10’, giving it an integrated magnitude of +6.2, within range of binoculars despite it horizon-hugging environment. M93 culminates at about 9pm an altitude of around 15° from the south of England. 

There’s a fine astro-photo opportunity on the night of 16/17 February when a first-quarter Moon passes under a degree south of Messier 45, the marvellous Pleiades open cluster in Taurus. As twilight fades, from about 6pm GMT, Taurus’ most westerly extremities, which includes the Pleiades, are very well-placed due south some 60° high. At this time the first-quarter Moon lies around 1.7° to the south-west of Alcyone (eta Tau, magnitude +2.8). Between 7pm and 1am GMT watch as the Moon approaches from the west, coming closest at about 9pm. 

The marvellous Pleiades

The Pleiades open cluster, designated Messier 45, in Taurus is as good as it gets for night-sky eye candy. There are only a handful of deep-sky objects that come close to its fame and sheer majesty. For newbie and experienced observers alike, its impact is not limited in any way: it is easily visible to the naked-eye in most skies and looks superb through a pair of binoculars or a small telescope, while owners of larger telescopes can explore in detail the wispy blue nebulosity that blankets its bright stars and imagers can capture the full depth of its grandeur.

Counting Pleiades

How many individual stars within the cluster can you see without optical help? There are in fact ten Pleiads (as individual stars here are often termed) that shine brighter than sixth-magnitude. The five brightest Pleiades — Alcyone (eta [η] Tauri, the brightest Pleiad, Atlas, Electra, Maia, and Merope — range from magnitude +2.9 to +4.2 and should be immediately apparent, but most people report six or seven. 

The cluster is traditionally known as the Seven Sisters, a reference to ancient Greek mythology, but as many as 14 to 18 Pleiads have been claimed by eagle-eyed individuals!

A binocular field of view easily encompasses M45, which, spanning two degrees across or four full moon-widths, is larger in angular extent than many expect. The wonderful view reveals some of the hundreds of fainter stars scattered around the brighter cluster members, including the aforementioned principal stars.

Beautiful blue nebulosity

Images of the Pleiades shows it’s substantially swathed in picturesque, wispy-blue nebulosity that’s courtesy of the blue-white light of Messier 45’s young stars being beautifully reflected and scattered by a huge, random dust cloud that the cluster is presently travelling through.

The brightest part of this nebulosity surrounds magnitude +4.1 Merope, the bright star at the southern corner of the ‘Plough’. Designated NGC 1435, a 250mm (ten-inch) telescope is a safe bet to pick it up under typical UK sky conditions.