A BUSY MOON MONTH

Daylight is progressively interfering with opportunities to observe the Moon visually in May. However, there is still plenty to see when the Moon is around after sunset, or at later phases in the early morning sky. On the morning of 3 May, libration, or the slight wobble of the Moon, exposes nearly seven degrees extra of the lunar far side near the lunar north pole. The libration effect is slightly stronger still on the 12th, with views of the far side, over on the western limb of the Moon. This may facilitate views of the eastern side of the Mare Orientale impact basin, such as the Montes Rook and Montes Cordillera, which are parts of the rings of this 3.8-billion-year-old impact basin – thought to be the Moon’s youngest. However, there may be issues with morning twilight and the lowness of the Moon in the sky making the observations a challenge.

New Moon is on the 16th, but you will need to wait at least a day or two for it to clear the evening twilight and appear as a narrow crescent. The earthshine part of the Moon will be very prominent, starting low on the horizon from approximately the 18th till the 22nd, when it will be higher in the sky and visible for longer, but more difficult to see due to the glare from the larger lunar phase. Although a Super Moon and various other so called named Full Moons are very popular to photograph and put out on social media, nothing beats the photogenic nature of the crescent Moon just above or silhouetted against the horizon, often embracing faint golden earthshine between the tips of its crescent.

On the 23rd between 21:10 and 23:00 BST the Lunar ‘X’ and Lunar ‘V’ clair- obscur (light and shadow) effects should be visible near Werner and Ukert craters, respectively. These are always pleasant to see, but are generally regarded as scientifically unimportant by more seasoned astronomers.

On the 24th, sunrise occurs across the flat floored amphitheatre-like crater Plato. Needle-like shadow spires will gradually recede across this as the lunar morning progresses from about 21:00 to 00:00 BST. Although you will not notice any movement by staring directly through an eyepiece in real time, go away and come back after about 15 minutes and you may see some difference in shadow positions and lengths. Shadow spire shortenings are more obvious when you do lapse video imaging. An even more rapid event occurs at around 23:13 BST (plus or minus several minutes on the same day, as seen from different parts of the UK) as the fifth magnitude star 79 Leonis is occulted by the Moon’s dark limb. Later, between 00:10 and 00:50 BST, there will be an opportunity to sketch or image Lassell crater, situated in eastern Mare Nubium, just south-west of crater Alphonsus, and to do a historical piece of detective work. A very detailed sketch of this crater was made under identical illumination, by Victorian astronomer, Thomas Elger, on 13 January 1886. Thomas Elger was the first director of the BAA’s Lunar Section, and had an eye for cartographic detail, having trained as a civil engineer. It will be very interesting to compare modern era observing with the Elgar’s acute eyesight.

On 26 May the Descartes region will be under very similar illumination to when Apollo 16 blasted off from the lunar surface on 24 April 1972.

Dr Tony Cook is the director of the BAA’s Lunar Section and a physics lecturer at Aberystwyth University.

COMETWATCH

10P/Tempel

THE DARK WANDERER

Comet 10P/Tempel (often referred to as Tempel 2) is a cornerstone of our understanding of ‘Jupiter family’ comets. Unlike the dazzling, long-tailed spectacles that have graced our skies in recent years, 10P/Tempel is a reliable, short- period visitor that orbits the Sun every 5.36 years (see last month’s cometwatch for an image). Tempel 2 is a remarkably large object (nucleus diameter of ~10 kilometres) that has expended much of its volatile ice and gas. It has an albedo of just 0.022, meaning it reflects only about two per cent of the sunlight hitting it. Scientists believe this ‘dark sheen’ is the result of billions of years of ultraviolet radiation from the Sun converting surface hydrocarbons into a thick, tar-like crust. This evolution has left only a tiny fraction – less than one per cent – of its surface active, making it a ‘highly evolved’ comet that outgasses mostly from a small region near one of its poles.

The comet’s perihelion distance is ~1.42 AU from the Sun, or just beyond the orbit of Mars, and its aphelion point lies at 4.71 AU from the Sun, near to the realm of Jupiter. One of its most intriguing characteristics is its ‘spin-down’. Astronomers have observed that the comet’s rotational period (currently about 9 hours) is gradually slowing down. This is caused by the ‘jet effect’ - as gas and dust erupt from the nucleus they act like thin thrusters, creating a torque that slowly brakes the comet’s spin.

Comet Tempel 2 will reach perihelion on 2 August but it is expected in the morning skies of May, with the best observing opportunities between 14 and 26 May when the Moon out of the way. Neil Norman

10P/TEMPEL

DATE

RA

DEC

TIME

ALT

MAG

14 MAY

19h 36m

-8° 19'

03:00

24°

+10

18 MAY

19h 44m

-8° 12'

02:30

21°

22 MAY

19h 51m

-8° 08'

02:30

22°

26 MAY

20h 01m

-8° 07'

02:30

20°

How to use this map

Face south, holding the star map with north at the top in front of you – the lower half of the map represents the part of the sky you are facing.

DATE TIME (UT)

TYPE OF EVENT

1 3

17:23 07:00

Full Moon Venus is 7° north of Aldebaran Antares is 0.5° north of the Moon (occultation southern South America, southernmost southern Africa) Eta Aquarid meteor shower maximum Last Quarter Moon Neptune is 4° south of the Moon Saturn is 6° south of the Moon Mercury is at superior conjunction Mars is 5° south of the Moon

03:00

6 9 13 13 14 15 16 19 20 22

21:10 09:00 22:00 14:00 01:00 20:01 02:00 13:00 14:00

New Moon Venus is 3° south of the Moon Jupiter is 3° south of the Moon Uranus is in conjunction with the Sun Regulus is 0.08° north of the Moon (occultation S. eastern Asia, N. south-eastern Asia) First Quarter Moon Full Moon Antares is 0.4° north of the Moon (occultation New Zealand, S. part of South America)

07:00

23 31

11:11 08:45

09:00

MAY

Mercury

Can be spied low over the north-western horizon soon after sunset towards the end of the month.

Venus

Is a splendid sight all-month as a blazing evening ‘star’ in first Taurus and then Gemini, where it reaches its greatest northerly declination at this apparition.

Mars

Finally emerges into the pre- dawn sky at mid-northern latitude, providing a real late- May challenge to locate for early risers and night owls.

Jupiter

Can be seen throughout the month as a brilliant object in the west soon after sunset, though only just by the end of May in Scotland and the far north of England.

Saturn

Has only just returned as a pre-dawn target, located on the boundary between Cetus and Pisces. It is best observed towards the end of the month, when it rises at about 03:00.

Uranus

Is in conjunction with the Sun on 22 May and is out of view all month.

Neptune

Rises just ahead of Saturn and owing to its low altitude in the pre-dawn twilight it is a tough telescopic target.

Dwarf planets

Makemake, in Coma, and Haumea, in Bootes, are evening targets for a large telescope and a sensitive camera.

MOON PHASES

Rise & Set Times BST

THE MOON

LIBRATION

DATE

DEG

POSITION ANGLE

3 May 12 May 23 May

6.6° 7.9° 7.2°

352° 108° 272°

DISTANCE

DATE TIME (BST) DISTANCE

DIAMETER

Apogee 4 May Perigee 17 May

23:32 14:49

405,843 km 358,076 km

29' 26" 33' 22"

TWILIGHT TIMES

At the start of May astronomical darkness persists from just 12.16 am to 2.11 am in Edinburgh. The degree to which the Sun is below the horizon determines the twilight experienced. Many observations can be carried out at the end of (evening) or beginning of (morning) nautical twilight.

Day sky

Horizon

Night sky

Sunrise/sunset

Sun 0–6° below the horizon Civil Twilight 6°–12° below the horizon Nautical Twilight

12°–18° below the horizon Astronomical Twilight

12°–18° = Astronomical

DATE LONDON (TIMES BST)

MANCHESTER

EDINBURGH

END TWILIGHT

NAUT.

ASTRO.

CIVIL

NAUT.

ASTRO.

CIVIL

NAUT.

ASTRO.

CIVIL 9.03pm 9.51pm 10.52pm 9.20pm 10.14pm 11.26pm 9.36pm 10.37pm 12.16am 9.20pm 10.14pm 11.30pm 9.38pm 10.38pm 12.16am 9.57pm 11.07pm 9.37pm 10.37pm 12.29am 9.58pm 11.06pm 9.52pm 10.99pm

–

10.15pm 11.33pm

– –

10.19pm 11.46pm 10.40pm 12.41am

–

– –

DATE

LONDON (TIMES BST)

MANCHESTER

EDINBURGH

START TWILIGHT

NAUT.

CIVIL

ASTRO.

NAUT.

CIVIL

ASTRO.

NAUT.

CIVIL

20 30

ASTRO. 3.06am 4.07am 4.56am 2.53am 4.03am 4.56am 2.12am 3.46am 4.46am 2.28am 3.42am 4.36am 2.04am 3.38am 4.37am 1.34am 3.19am 4.19am –

– –

3.10am 4.17am 2.44am 4.01am

– – –

3.15am 4.24am 2.37am 4.01am 1.47am 3.42am

3.00am 4.06am

DATE May 05

MAG –26.7

SIZE 31'.7

PHASE N/A

RISE

CULM

SET

DIST

SUN

May 15

May 25

–26.7

31'.6

N/A

RA 02h 48.1m 03h 27.1m 04h 07.1m

DEC +16° 11' +18° 48' +20° 54'

05:24

05:07

04:53

12:57

20:31

20:47

21:02

1.008

1.011

1.013

MERCURY

May 05

May 15

May 25

–1.1

–2.3

–1.2

5".2

5".1

5".5

92.0%

99.9%

87.0%

02h 07.4m 03h 28.7m 04h 58.2m

+11° 22' +19° 07' +24° 23'

05:13

05:09

05:22

12:18

13:01

13.51

19:26

20:56

22.22

1.288

1.322

1.227

VENUS

May 05

May 15

May 25

–3.9

–4.0

11".8

12".2

12".8

87.0%

84.5%

81.7%

04h 46.0m 05h 38.4m 06h 31.1m

+23° 26'

+24° 48'

+25° 01'

06:35

06:38

06:50

14:56

15:09

15:22

23:17

23:40

23:54

1.418

1.362

1.301

MARS

May 05

May 15

May 25

+1.2

+1.3

4".2

97.6%

97.2%

96.8%

01h 12.9m 01h 41.4m 02h 09.9m

+06° 48' +09° 40' +12° 22'

04:43

04:16

03:51

11:21

11:10

10:59

18:01

18:05

18:09

2.238

2.220

2.199

JUPITER

May 05

May 15

May 25

–2.0

–1.9

35".2

34".3

33".6

100%

07h 24.6m 07h 31.3m 07h 38.6m

+22° 25' +22° 11' +21° 55'

09:20

08:49

08:19

17:31

16:58

16:26

01:45

01:11

00:37

5.602

5.743

5.872

SATURN

May 05

May 15

May 25

+0.9

16".1

16".3

16".5

100%

00h 38.7m 00h 42.6m 00h 46.2m

+01° 48'

+02° 11'

+02° 32'

04:34

03:57

03:19

10:46

10:11

09:35

16:58

16:25

15:51

10.289

10.184

10.061

URANUS

May 15

+5.8

03".4

100%

03h 55.9m

+20° 13'

05:28

13:23

21:19

20.469

NEPTUNE

May 15

+7.9

02".2

100%

00h 15.6m

+00° 14'

03:40

09:43

15:47

30.514

CERES

May 15

+8.7

00".7

100%

03h 31.0m

+15° 27'

05:34

12:59

20:24

3.796

PLUTO

May 15

+14.5

00".1

100%

20h 35.8m

–22° 51'

02:08

06:04

10:00

35.181

ERIS

May 15

+18.8

N/A

100%

01h 49.9m

+00° 12'

05:14

11:17

17:21

96.376

MAKEMAKE

May 15

+17.2

N/A

100%

13h 25.2m

+20° 56'

14:53

22:51

06:53

52.062

HAUMEA

May 15

+17.2

N/A

100%

14h 41.6m

+14° 36'

16:48

00:11

07:30

48.995

JUPITER MOON EVENTS

DATE

TIME

EVENT

1 1 1 2 2 3 8 9 10

22:25 23:10 23:38 22:29 23:35 22:03 22:58 23:17 23:12

III ShE II ShI II TrE I ShI I TrE I EcR III ShI I TrI II EcR

All times BST. KEY: I Io; II Europa; III Ganymede; TrI and TrE transit start and end; ShI and ShE shadow-transit start and end; EcR eclipse reappearance.

GRS transits

DATE

TIME

3 5 10 15

21:42 23:23 22:33 21:43*

Events based on an estimated mid- month GRS system II longitude of 89°. Times BST. * event in strong twilight

ASTEROIDS

(116) SIRONA AT OPPOSITION 3 MAY

(70) PANOPAEA AT OPPOSITION 16 MAY

(21) LUTETIA AT OPPOSITION 30 MAY

DATE

RA

DEC

MAG

14h 45m 08s

–13° 46' 08"

+10.9

14h 34m 39s

–13° 16' 30"

+11.3

14h 23m 43s

–12° 51' 20"

+11.7

15h 45m 12s

–21° 04' 24"

+11.4

15h 29m 50s

–21° 45' 34"

+10.9

15h 13m 35s

–22° 15' 30"

+11.2

16h 53m 06s

–20° 49' 38"

+11.0

16h 43m 53s

–20° 47' 13"

+10.6

16h 29m 23s

–20° 38’ 29”

+10.0

44 Boötis

44 BOÖTIS (SAO 45357)

RA 15h 03.8m

DEC +47° 39'

Eight degrees north of magnitude +3.5 Neckar (beta [β] Boötis), the star at the top of Boötes’ kite-shaped asterism, lies a line of three faint naked-eye stars extending north-east to south-west. The preceding (westerly) of these is STT 291, a rather wide and very unequal pair with magnitude +6.3 and +9.6 stars separated by 25 arcseconds at position angle (PA) 156 degrees. The middle star is 44 Boötis, also known as i Boötis and in double star catalogues as H I 15 and STF 1909.

In 1781, William Herschel noted that “With 227 they seem almost to touch” and “This is a fine object to try a telescope, and a miniature of alpha Geminorum”. It was another 40 years before the stars were observed again, this time by Wilhelm Struve, having closed to a separation of 0.2 arcseconds during this time. Another close approach occurred around 2020 – I managed to measure the stars on one night in 2016 when they were at a separation of 0.9 arcseconds and closing quickly. They are now 0.85 arcseconds apart and widening rapidly, although the difference in magnitudes (+5.2 and +6.1) suggests that an aperture of 200 mm (eight inches) should comfortably show them.

The primary is a type F7 dwarf, whilst the double companion contains stars with spectral types G2V and K4V. The companion is a well-known eclipsing variable of the W Ursae Majoris class with a period of 0.2678 day, whose variability had been suspected in the nineteenth century but was confirmed by Jan Schilt in 1926, using the Mount Wilson 60-inch telescope. 44 Boötis lies 41 light- years away.

Bob Argyle

Follow T Cephei’s brightening

A decade ago, the Mira type variable T Cephei reached maximum during May, peaking close to its long-term average of magnitude +6.0. There was a significant ‘pause’ during its rise to maximum.

The period of T Cephei is catalogued at 389 days. Hence it should reach maximum around 24 days later each year. Given this value, a decade later, we would expect T Cephei to now be reaching maximum during the winter months. It is, however, peaking during June. Moreover, the ‘pause’ seems to have moved to its fade from maximum. Maxima are also falling some way short of the average of +6.0, and Minima have also tended to be less faint than the long-term average.

Despite this, the range of T Cephei is still more than three magnitudes and its brightness changes are therefore readily followed visually, although large binoculars or a telescope will be needed to see it when near minimum. Observations made a few times each month will allow the brightness changes to be easily followed. The monitoring of Mira type variables is largely dependent on amateur astronomers and such observations allow professional astronomers to understand these stars better.

With maxima in recent years occurring during June, T Cephei can be seen brightening towards maximum during the spring months and fading during the autumn. Helpfully, it is circumpolar, lying in the vicinity of beta Cephei. A copy of the BAA VSS finder chart can be downloaded from britastro.org/vss/xchartcat/T%20Cep.htm

T Cephei is a red giant star that is in the final stages of its evolution. Despite being a giant star that would extend beyond the orbit of Mars if placed at the centre of our Solar System, it has a mass only around half that of our Sun. The brightness variations are related to pulsations in its tenuous outer layers. Eventually it will gradually shed these outer layers leaving just a white dwarf star.

Tracie Louise Heywood

Eclipse mid-times (UT):

RZ Cas (Duration 4.8 hours): April 24d 21.6h, 30d 21.0h, May 2d 1.7h, 8d 1.2h, 14d 0.6h, 20d 0.0h, 25d 23.4h, 31d 22.9h. U Cephei (Duration 9 hours): April 25d 1.3h, 30d 1.0h, 5d 0.6h, 10d 0.3h, 15d 0.0h, 19d 23.6h, 24d 23.3h, 29d 23.0h. Beta Lyrae (primary): April 23–25, May 6–8, 19–21. Beta Lyrae (secondary): May 1–2, 13–14, 26–27.

Binocular Mira Variables:

Rising :T Cep, S CrB. Maxima : R And (early May, average peak mag +6.9), RS Her (mid, +7.9), X Oph (mid, +6.9), R Tri (late, +6.0), R LMi (late, +7.1). Fading : U Her, R Ser, S UMa.

Tip your hat for

THE SOMBRERO

M104, the Sombrero Galaxy is a stunning example of an edge-on spiral galaxy, while M83, the Southern Pinwheel, is a face-on gem, writes Mark Armstrong.

M104: FAST FACTS

NAME: The Sombrero Galaxy DESIGNATION: Messier 104, NGC 4594 CONSTELLATION: Virgo RA: 12h 40m 00s DEC: –11° 37' 34" MAG: +8.3 APPARENT DIAMETER: 8.9' × 4.1' CLASS: SA(s)a; edge-on DISTANCE: 28 million light years PHYSICAL DIAMETER: ~100,000 light years DISCOVERY: 1781 by Pierre Méchain

Messier 104 (NGC 4594), the Sombrero Galaxy, is one of the iconic deep-sky objects. Its magnificent and striking form includes a stunning dust lane that is a big part of its likeness to a Mexican hat. It is unquestionably right up there in the conversation with the likes of the Orion Nebula (M42) and the Andromeda Galaxy (M31), as it is arguably the best example of all of an edge-on spiral galaxy. Today many deep-sky objects have acquired popular nicknames, whether they are appropriate or not. If you are yet to familiarise yourself with M104 then, looking at the image above, you are assured the Sombrero Galaxy is a fit and proper nickname; its encompassing dust lane and huge central bulge and halo, all superbly imaged by today’s amateur imagers, are reminiscent of the rim and high top of a Mexican hat.

The Sombrero was discovered by Pierre Méchain in 1781, too late to be entered into the original version of Charles Messier’s ubiquitous catalogue of bright deep-sky objects. In 1921, French astronomy writer Camille Flammarion found Messier’s original note about his independent observation and Messier 104 came to be. William Herschel, the relentless and perhaps most famous deep-sky observer, saw the dark lane, later described in 1833 as a ‘dark interval or stratum’ by his son John.

One fly in the ointment for observers and imagers at mid-northern latitudes is that the Sombrero lies south of the celestial equator, among the stars along the boundary between southern Virgo and northern Corvus. It is located around 10° west and south of Virgo’s alpha and gamma stars, Spica and Porrima, respectively. M104 culminates a few degrees under 30 degrees in elevation, hindering observations from UK shores.

On a moonless and transparent night at a dark sky location, M104 may be seen as a small nebulous patch through 10 × 50 or larger binoculars, though a small telescope, with its superior light grasp, is a better choice. Try tracking it down around mid-May, when the Moon is out of the way, though for those suffering most from this month’s twilight-plagued skies, April is a better bet.

M83: the stunning Southern Pinwheel

With splendid southern galaxies in mind, observers based well north of the equator perhaps think initially of Centaurus A (NGC 5128 and Caldwell 77) and the Magellanic Clouds. The trio, sadly, never rise in the UK, though the former creeps 10 degrees high from southern Spain and offers more comfortable viewing at the Florida Star Party.

One magnificent southern galaxy that can be seen from UK shores is Messier 83 (NGC 5236). Its barred, face-on glory has rightfully ordained it as the Southern Pinwheel (M101 in Ursa Major is the Pinwheel Galaxy). Known as a starburst galaxy for its elevated rate of star formation (six supernovae have been discovered here too), M83 is located 30 degrees south of the celestial equator in the far eastern reaches of the long and meandering southern constellation of Hydra. Consequently, it barely climbs to 10 degrees above the southern horizon from the south of England. M83 is, of course, a prime target for remote imaging.

The Southern Pinwheel lies just under 20 degrees south of Spica and 7.8 degrees south-east of magnitude +3 gamma Hydrae. At mid-May, M83 culminates at 23:00 BST from London. Shining relatively brightly at magnitude +7.6, it is an easy binocular object from the Southern Hemisphere, but in the UK a telescope is recommended to track it down. The best you will see is a nebulous smudge, but at least you will be able to boast that you have seen the farthest south-lying galaxy in Messier’s catalogue.

THE SOUTHERN PINWHEEL (M83 & NGC 5236)

RA 13h 37m 00s

DEC –29° 52' 04"

MAG +7.6

SIZE 11' × 10'

Sample late-spring’s

DEEP-SKY DIVERSITY

The variety of deep-sky objects in the late- spring sky makes for a great night’s observing, writes Mark Armstrong.

MESSIER 5 (NGC 5904)

RA 15h 18m 33s +02° 04' 58"

DEC

MAG +5.7

SIZE 17'

Late-spring’s ever-dwindling night time and growing twilight make deep- sky observing increasingly challenging, but there is still time before the early- to mid-summer hiatus to experience the sheer diversity the deep sky offers at this time of the year. At nightfall, the swarming galaxy fields of the likes of Virgo, Coma and Ursa Major are optimally presented, to be replaced after midnight by the prime globular cluster hosts Hercules and Ophiuchus. Rising to prominence in the east, dominant Cygnus and its surrounding summer-sky retinue are prime targets for all kinds of nebulae.

Get your bearings via asterisms

May signals the end of astronomically dark skies (twilight-free) in the UK, with the south of England holding on to true darkness until late in the month. Scotland and the north of England are really penalised for the majority of May, suffering much more debilitating lighter nights.

Diffuse and extended deep-sky objects such as galaxies and nebulae are harder to observe under such conditions, but the brighter globular and open clusters such as M3, M13 and M11 remain good targets. Unless local skies are severely light-polluted, most constellations can be pinpointed by bright star patterns called asterisms, distinct patterns of stars separate from the (generally) larger constellations. Large and famous examples are the Summer Triangle (Vega, Deneb and Altair) and the Plough in Ursa Major, the Great Bear. The March issue of Astronomy Now focused on the Plough and how its star pattern can act as a celestial signpost to other important parts of the night sky.

Following the handle of the Plough south and east by some 30 degrees leads to brilliant Arcturus, a classic type-K red giant that at magnitude –0.04 is the

THE COMA STAR CLUSTER (MELOTTE III)

RA 12h 25m 06s +26° 07' 00"

DEC

MAG –

SIZE 275'

brightest star north of the celestial equator (Sirius lies in the southern sky). Arcturus is the alpha star of Boötes, the Herdsman, a substantial constellation whose form stands tall, spread out south to north from seven to 55° declination but covering just 20° or so east to west at its widest point. Boötes hosts its own well-known asterism, a huge, kite-like shape that spans 23 × 10 degrees, with Arcturus anchoring the ‘kite’ and Nekkar (beta Boo, mag. +3.5) at the northern tip.

Following the curve of the Plough’s handle past Arcturus south and westwards by another 30 degrees or so leads to first-magnitude Spica, the alpha star of Virgo. Around 15 degrees north-west of Spica is Porrima (gamma Vir, mag. +2.7), the storied binary star that forms the base of the ‘bowl of Virgo’, the well-known asterism that holds many bright galaxies.

Melotte III: The Coma Star Cluster

For a week either side of mid-May the Moon (new on the 16th) has no or minimal effect on deep-sky observing. At nightfall mid-month, the meridian bisects the constellation of Coma Berenices and the sprawling Melotte III (Cr 256), an open cluster better known as the Coma Star Cluster. At a dark-sky location, the Coma Star Cluster can be seen with the naked eye, but a pair of binoculars are ideal to observe its loose nature covering four to five degrees of sky.

Magnitude +4.4 gamma Comae Berenices is the cluster’s brightest star, marking its northern extremity, tucked away in Coma’s north-western corner. Five of its fifth-magnitude stars, Flamsteed-designated 12, 13, 14, 16 and 17 Com, form a triangular pattern. Overall, Melotte III hosts around 40 stars shining between magnitude +5 and +10.

Pulcherrima: a wonderful double star

Let us head west to Boötes’ aforementioned Kite asterism to observe Izar (epsilon Boötis), a star about halfway up the kite formation. Izar is one of spring’s best double stars, marvellously named Pulcherrima, Latin for ‘most beautiful’, or ‘loveliest’, by F.G.W. Struve. Despite its epsilon designation, Izar is the second-brightest star in Boötes, shining brightly at magnitude +2.3.

Pulcherrima is a great sight through even a small telescope, a splendid colour contrast between a magnitude +2.7 class-K0 orange giant and a magnitude +5.1 white class-A2 main sequence dwarf that shows a noticeable bluish hue. The pair are separated by an easy-to- split 2.8 arcseconds.

PULCHERRIMA (IZAR & EPSILON)

RA 14h 44m 59s +27° 04' 29" +2.7 & +5.1 2.8"

DEC

MAGS

SEP

Messier 5: a bright globular

Head 23 degrees south-east of Arcturus and you will arrive in close proximity to Messier 5 (NGC 5904), in Serpens Caput. Along with M3 and M13, M5 is one of the great globular clusters of the northern sky. M5 shines at magnitude +5.7 and shows up as an unresolved patch of light through binoculars 22 arcminutes north-northwest of the star FL 5 Serpentis (HIP 74975, magnitude +5.4), which places it just north of the celestial equator in south-western Serpens.

A small telescope can pick out M5’s outlying stars and show it is slightly elliptical in shape. Through a 150–200 mm (six- to eight-inch) telescope on a steady and transparent night, individual stars can be resolved to M5’s core. Deep images show Messier 5 extends to 17 arcminutes in apparent diameter.

The largely southern constellation of Ophiuchus looms large to the east of Serpens Caput. Along with Sagittarius, Ophiuchus is well known for its crop of seven Messier-designated globulars. The close pairing of M10 and M12, together with M14, are the most accessible at mid-northern latitudes.

NGC 6210: The Turtle Nebula

The impressive and large constellation of Hercules dominates May’s post-midnight southern sky. Although covering a massive 1,225 square degrees, ranking it the fifth-largest of the 88 present-day constellations, Hercules is not hard to locate, boasting the ‘Keystone’, a bright asterism of four third- to fourth-magnitude stars. The great globular M13 lies on the Keystone’s western side between eta (mag. +3.5) and zeta (+2.8).

The Turtle Nebula is a fine planetary nebula that lies around 8° south of zeta, with magnitude +2.8 Kornephoros (beta Her) found 4° to the south-west. An 80 to 100 mm (3- to 4-inch) telescope shows the nebula’s ninth-magnitude glow as a patch of high-surface-brightness nebulosity with a distinctive green–blue hue. Deep images can show the Turtle’s wispy, visually elusive ‘flippers’.

THE TURTLE NEBULA (NGC 6210)

RA 16h 44m 29s +23° 47' 58"

DEC

MAG +8.8

SIZE 48"

Behemoth Deneb and the North America Nebula

By the small hours Cygnus, the Swan, one of the signature constellations of the summer sky owing to its shed-load of bright nebulae, lies high in the east. Between here and Hercules we have bypassed Lyra, home of brilliant Vega, the brightest star (mag. +0.03) in the Summer Triangle asterism, and Messier 57, the impressive Ring Nebula, the high-surface brightness planetary nebula that is well worth observing.

Vega visually dominates the Summer Triangle, but Deneb, Cygnus’ alpha star (+1.25) and the Triangle’s faintest and most northerly lying star, reflects the adage ‘never judge a book by the cover’. Deneb is a monster star, a class-A2 supergiant that lies an incredible 1,425 light years distant, placing it almost 60 times farther away than Vega. Deneb is one of the most intrinsically bright stars in its class, which gives it an amazing absolute magnitude of –7.09 (Vega is +0.6).

Deneb has a further string to its bow as one of the few bright stars that form an integral part of two famous asterisms. Cygnus’ brightest stars, including Deneb, form its large ‘Northern Cross’ asterism.

Adjacent to Deneb (three degrees east) is the iconic North America Nebula (NGC 7000 & Caldwell 20), a vast H-II region, or emission nebula, spanning a substantial 120 × 100 arcminutes (about four full-Moon widths) that bears an uncanny resemblance to the North American continent. Those blessed with the last vestiges of spring’s dark skies and a lack of light pollution should easily pick it up through a pair of binoculars. The low-power view through a small telescope is enhanced by adding a UHC or Oxygen-III filter.

NORTH AMERICA NEBULA (NGC 7000 & CALDWELL 20)

RA 20h 58m 00s

DEC +44° 20' 00"

MAG –

SIZE 120' × 100'

SMARTSCOPE CORNER

Each month Stuart Atkinson chooses a pair of excellent targets for your Smartscope imaging pleasure.

M101: the magnificent Pinwheel Galaxy

There are many beautiful spiral galaxies in the May sky worthy of your Smartscope’s attention, but M101 in Ursa Major, the Great Bear, is one of the most beautiful. Lying 23 million light years from us, this galaxy is oriented face on to us and is about as perfect a spiral as it is possible to capture. Its faint magnitude of +7.7 and low surface brightness mean it is faint visually, but it could almost have been designed for Smartscope photography; you will love seeing its image build up as you take your exposures. For the best results take a lot of exposures from a dark sky site, then you will capture a wonderful portrait of M101’s bright core and sweeping, tightly wound spiral arms. With a little processing you will be able to bring out structure in those arms, knots of star clouds and the subtle pink glow of smaller star-forming regions too.

M3: a special globular cluster

M13 may be the best known and most imaged globular star clusters in the northern sky, but M3, in Coma Berenices, is often overlooked, which is a shame because it is just as beautiful an object. A bloated ball of an estimated half a million ancient stars, M3 is 33,000 light years away, making it even farther from us than the centre of the Milky Way. It is visible as an out-of-focus star to the naked eye, but your Smartscope will resolve it into a beautiful cluster of stars, with a very rich, bright centre. It is best to image M3 – like all globular clusters – on a Moon-free night, to let your Smartscope capture as many of its faintest, outlying stars as possible.

by Owen Brazell

Globular NGC 4147 in Coma

NGC 4147

RA 12h 10m 06s +18° 32' 30"

DEC

MAG +10.4

SIZE 4.4'

NGC 4147 is the least known of the globular clusters in Coma Berenices, after Messier 53 and NGC 5053. Discovered by William Herschel in 1784, NGC 4147 lies around 60,000 and 70,000 light years from Earth and the galactic centre, respectively. It is thought to be part of the outer halo of globular clusters surrounding the Milky Way, though it may lie in the transition zone. NGC 4147 is quite a small globular cluster, about 110 light years across. This suggests that the distribution of its stars is rather sparse.

NGC 4147 is thought to have been acquired by the Milky Way from another galaxy merger, perhaps the GAIA–Enceladus merger of about 11 billion years ago. However, there are suggestions that it is part of the Sagittarius tidal stream and thus acquired from the Sagittarius dwarf elliptical galaxy.

Despite the fact that it is not that well known, NGC 4147 appears in many observing lists. It should be visible in a 150 mm (six-inch) aperture, although it may appear no more than a hazy patch. Larger telescopes at higher power should be able to resolve some of its stars. Under the Shapley–Sawyer classification it is type IX, so quite loose.

How to use this map

Face north, holding the star map with south at the top in front of you – the lower half represents the part of the sky you are facing.

Mercury

Will be very difficult to spot in late May hugging the north-western horizon soon after sunset.

Venus

Is a dazzling evening ‘star’ making good progress in accessibility in the north-western sky.

Mars

Climbs steadily in the pre-dawn sky though the Red Planet brightens only marginally as it does so.

Jupiter

Shines brightly in the early-evening north- western sky as Venus draws ever-closer towards next month’s close conjunction.

Saturn

Quickly establishes its unmistakable presence in the pre- dawn sky, located on the boundary between Cetus and Pisces.

Uranus

Is in conjunction with the Sun on 22 May and is out of view all month.

Neptune

Can be located in Pisces with large binoculars in the pre-dawn sky, some seven degrees above Saturn.