Picture of the Month for 2021

• December 2021 - Picture of the Month

  Planetary Nebula HDW 2 (Sh2-200) in Cassiopeia

  

  I thought that it was about time for another planetary nebula. Not that you'd guess that from this object's designation: it was discovered and misclassified as an HII emission nebula by Stewart Sharpless, finding its way into the Sharpless catalog. In fact it wasn't until 2017 that a spectra was taken that definitively settled the nature of HDW 2.

  HDW 2 is an old planetary nebula that is beginning to fade into the background. The bright shell in Don's image is about 6' in diameter, whilst Hartl and Weinberger (1987) felt that the Palomar Observatory Sky Survey (POSS) plates showed an outer halo of about 24' diameter as well. I've checked, and whilst it might be there, it could also be 'averted imagination'. They also estimated HDW 2 to be about 580pc (about 1900 light-years) from us, but don't say how.

  Fortunately Corradi et al (2003) undertook narrow-band studies which show this outer halo much more clearly, and suggest it's 30' in diameter, which at 580pc is huge. What they're not sure about is whether this faint structure is part of the planetary nebula or an interaction with the Interstellar Medium (ISM).

  As to the central star there seems to be no concensus. A hot white dwarf would be expected, and given that HDW 2 is relatively close to us it's a surprise that none has been conclusively identified.

  The view of the Strasbourg-ESO Catalogue of Galactic Planetary Nebulae (Acker+, 1992) seems to be that the central star is of spectra type A and 12.6V magnitude, designation TYC 4053-643-1. Unfortunately they also add a note to say It is not clear if the A-type star observed is the true central star of the nebula.

  The spectroscopic survey of Weidmann and Gamen (2011) supports the A-type classification, but they also conclude that the central star is a binary. More recently Bear and Soker (2017) have concluded that the central star, whichever it might turn out to be, may be a triple system. Their work is based on the irregular morphology of the planetary nebula which they claim cannot be explained by a binary.

  Professional debate aside, studying low surface brightness objects like these is what astroimaging does best, and even the inner shell of this wonderful object is full of structure revealed in O-III. There's also more than a hint of that extended halo in the lower-right corner of this image where it is brightest.

  James Whinfrey - Website Administrator.

• November 2021 - Picture of the Month

  NGC 1365 in Fornax

  

  I've surprised myself by picking another galaxy for Picture of the Month.

  NGC 1365 is a popular target it seems, though for those of us in Northern Europe it barely scrapes the horizon as a prominent member of the Fornax cluster, and about 55 million light-years away. It's not hard to see the reasons for this popularity: it's a glorious and large barred-spiral galaxy, its arms dotted with starforming regions and streaked by dust. As you'd expect with all that star-formation going on, NGC 1365 has hosted a number of supernovae, I believe four, with the last in 2012.

  At the heart of the bright core in Martin's image lies a rapidly-rotating supermassive blackhole of 5–10 million solar masses. NGC 1365 is classed as a Seyfert galaxy, with its core being studied in a range of wavelengths by professional astronomers. The suspicion is that bar helps channel matter in towards the blackhole.

  So there's plenty to keep those with cameras busy, but what about those of a visual persuasion? The Night Sky Observer's Guide Volume 1 suggests that a bright core with a faint halo is visible in a 20-cm telescope, but to get the best of this galaxy needs a much bigger scope, the bigger the better: it gets an Impressive! in a 50-cm instrument.

  James Whinfrey - Website Administrator.

• NGC 474 and NGC 470 in Pisces

  October 2021 - Picture of the Month

  

  I've cheated, I'll admit it, this isn't an amateur image. It's part of the Dark Energy Survey (DES) being conducted by a number of the World's foremost scientific organisations. They're using the Víctor M. Blanco 4-meter Telescope in the Chilean Andes, but amateurs are using remote equipment these days, and some are not much smaller.

  It is an impressive sight all the same, and a pro image is my Picture of the Month since I failed to get permission in time to use an amateur image of the same galaxies (NGC 474 and NGC 470) by Marco Lorenzi, which you should go and look at on his own website anyway because it's excellent. Marco's version actually contains an additional galaxy NGC 467.

  NGC 474 is the elliptical galaxy in the image, also known as Arp 227, and the wonderful spiral is NGC 470. Those shell-like structures in the former, or perhaps tidal tails, have been taken as evidence of recent mergers. There's also speculation as to whether they're caused by tidal interaction with NGC 470.

  Given that these galaxies are about 100–110 million light-years from us, it's impressive that a team from the Leibniz Institute for Astrophysics Potsdam (AIP) used long exposure images from the MUSE instrument on and even bigger telescope, the VLT, to identify a number of globular clusters and planetary nebulae amongst the stars of the outer shell of NGC 474.

  So apart from being a terrific imaging target, and clearly of scientific interest too, can you observe these galaxies visually? The Night Sky Observer's Guide (NSOG) Volume 1 provides an eyepiece sketch at 200x with a 12.5in telescope from dark skies, and with a scope in the 8–10in range both galaxies should be visible. I wouldn't hold out much hope of seeing those shells though.

  James Whinfrey - Website Administrator.

• Sharpless 126 (Sh2-126) in Lacerta

  September 2021 - Picture of the Month

  

  I'm fascinated by the large scale structure of the deep-sky. Unfortunately, as a visual observer, unaided by electronics, this is something that's impossible to view directly. So enter the astrophotographer with inspiring wide-field views like this one.

  Thomas has captured a feast of deep-sky objects in this 5 degree field, and the image on his website labels the main ones very nicely when you mouse-over. As you'd expect from a region like this, there are many bright nebulae, a few herbig-haro objects, a loose open cluster (ASCC 122), and even a couple of NGC galaxies.

  Sharpless is catalogued as being centred in the top part of this image, right at a bright knot in LBN 437 which is full of active star formation. Its also noted to be 160 arc-minutes in extent, but as you can clearly see the nebulosity extends significantly further than that in the north-south direction; nearly 240 arc-minutes. This is large HII region of which Sharpless 126 is only a part, and its size is in part due to its proximity at about 2000 light-years.

  All of this is illuminated by 10 Lacertae which is near the centre of the image and the brightest star in the area. 10 Lacertae is a massive O9V star, a suspected beta Cepheid, and an optical double with an 10th magnitude companion (S 813) about an arc-minute away. There's a 15th magnitude companion (TRN 36) at only 3.6 arc-seconds, which seems very challenging observation to me! Its nature is uncertain. Most of the bright stars here, including 10 Lacertae, are members of the Lacerta OB1 association.

  It's worth mentioning that 8 Lacertae near the centre of the nebulosity has featured as one of Bob Argyle's Double Stars of the Month, back in October 2009.

  James Whinfrey - Website Administrator.

• August 2021 - Picture of the Month

  Abell 61 in the Constellation of Cygnus

  

  No planetary nebulae in Picture of the Month since December 2019! That one was an Abell planetary nebula too, Abell 6. So it was high time to feature another, and since Patrick has pointed out plenty for visual observers recently, I felt compelled to choose something much fainter.

  Abell 61 is about 4.5 degrees to the WSW of delta Cygnii sitting just off Cygnus's northern wing tip around 4600 light-years away. As you can see, it's approximately round with a little distortion to the lower left side and differential brightening of the rim that seems to be caused by interaction with the interstellar medium (ISM). It's an old planetary nebula, and therefore a faint one, with a visual magnitude of 13.5 spread over its 3.4 arc-minutes diameter.

  The central star is magnitude 17 hot variable of about 0.5 solar mass that may, or may not, be a close binary. I believe the star is captured in this image (the bluish point) along with some subtle internal detail and a number of faint background galaxies.

  According to the Night Sky Observer's Guide (NSOG) Abell 61 is just visible with an O-III filter through a 16–18inch telescope, so all's not lost for the visual observer.

  I love the subtlety of the planetary nebula in this image. It appears to be emerging from that bank of bright stars.

  James Whinfrey - Website Administrator.

• The Eagle Nebula (M16) in Serpens

  July 2021 - Picture of the Month

  

  I can't quite believe that I've failed to feature an image of this object. The Eagle Nebula (Messier 16) is an imagers' favourite that even those of who are eyeball-oriented astronomers can observe.

  I think that Nik's image makes a terrific composition of all that star-forming glory. We have the 'Pillars of Creation' featured in the centre with the 'Stellar Spire' seeming to be projected towards the Eagle's head from the left. Both structures hide newly-formed stars within them.

  Buzzing around the Eagle's head are the stars of open cluster NGC 6611, over 500 of them according to Archinal and Hynes. All are young, massive and very luminous. This cluster is responsible for the cavity in the dust cloud that give the Eagle nebula its shape, and illuminated the Pillars.

  James Whinfrey - Website Administrator.

• Bernes 149 in Scorpius

  June 2021 - Picture of the Month

  

  After last months galaxies I've returned to our own with an image of a particularly stiking reflection nebula. Striking because it's set against that band of dark nebula from which it's emerged thanks to those eye-searing stars near the centre of the image. What a composition.

  This is the Lupus 3 dark cloud, one of several in a complex that is producing many of the new low mass stars in our vicinity, and home to the reflection nebula GN 16.05.2 which is illuminated by HR 5999, the lower of those two central stars. This pair of stars are an exception to the Young Stellar Objects (YSOs) typically found in the region. They're both Herbig Ae/Be stars: more massive than most and precursors of supergiant stars.

  Both Lupus 3 and these stars have been the target for detailed imaging and measurement by professionals seeking to learn more about star formation, and the VLT resolved a circumstellar dusty disc around HR 5999 in the mid-infrared.

  However on this occasion I've chosen Fabian's wonderful image because it's a reminder of how much fascinating structure there is in the night sky.

  James Whinfrey - Website Administrator.

• The Arp 286 Galaxy Group in Virgo

  May 2021 - Picture of the Month

  

  I could talk about Halton Arp and his inclusion of these three galaxies in his Atlas of Peculiar Galaxies, or about the signs of interaction clearly visible in this image, or perhaps even the interesting structure presented here.

  But Owen is much better at that, so why not read his Galaxy of the Month feature for this month to learn more about this fabulous group, including how to observe them.

  Honestly, I picked this image because interacting groups of galaxies are beautiful. Owen also has a link to another incredible amateur image.

  James Whinfrey - Website Administrator.

• The Southern Pleiades (IC 2602) in Carina

  April 2021 - Picture of the Month

  

  It was time for another open cluster and Marco's image of IC 2602 caught my eye with its light haze of nebulosity and punchy crisp stars.

  IC 2602 isn't a rich cluster with about 60 members spread over its 100 arc-minute diameter. This is a binocular object and the 5th and 6th magnitude main members are easily observed in any small instrument, or naked eye. However, most of the members are fainter than those of the Pleiades in Taurus.

  What isn't fainter is that central star, Theta Carinae. It's a large (around 15 solar masses) blue star that appears to be significantly younger, at a tenth of the age, than open cluster of which it's a member. The reason for this is that it's a blue straggler: a star that has been rejuvenated by the transfer of mass from a neighbouring star. These aren't common in open clusters so this is a special star worthy of featuring itself.

  Right below Theta Carinae (to the south) you can see a faint condensation of stars on the border of the image. This is another open cluster called Melotte 101 which is much further away than IC 2602: around 6500 light-years rather than 540. It adds some stardust sparkle to the field of view.

  James Whinfrey - Website Administrator.

• Spiral Galaxy NGC 3432 in Leo Minor

  March 2021 - Picture of the Month

  

  Another galaxy! Actually two, but the main event is that edge-on spiral in which David has captured the patterns of dust and star formation. I said two didn't I. Actually this image is full of faint PGC galaxies once you start to look carefully. I also particularly love the framing of that trio of bright 10 magnitude stars.

  David's notes

  NGC 3432 has a magnitude of 11.3 and was discovered by William Herschel on March 19, 1787. It is some 45 million light-years away and its distinctive shape is due to the ongoing gravitational interaction with UGC 5983, a magnitude 16.3 dwarf galaxy to the southwest of NGC 3432. This interacting pair of galaxies is included in Arp’s catalogue with the label Arp 206.

  Data were gathered over several nights between 26 March and 15 April 2020 and comprised 25 x five-minutes luminance and 10 x five-minutes each of RGB, binned 2 x 2. I used an 8-inch Ritchey-Chretien with a QSI 683 camera.

  James Whinfrey - Website Administrator.

• Spiral Galaxy NGC 2403 in Camelopardalis

  February 2021 - Picture of the Month

  

  I've gone for a galaxy this month because we're heading towards season, and besides when was the last time I had one on Picture of the Month (it was May 2020). So if you're going to choose a galaxy it might as well be a spectacular example of its kind.

  I think that NGC 2403, as presented here by David Ratledge, is just that: a bright spiral galaxy actively forming stars and hence supernovae. It's part of the M81 group, and relatively local to us at about 10 million light-years. It's been the subject of more than one APOD, and it was even Galaxy of the Month in January 2013.

  Most importantly it's a galaxy that I've managed to observe from my light polluted home even marking it as worth a revisit. It was caught at relatively low power (x64) with my 10-in scope, as always a darker sky would have been helpful. I didn't catch much detail that night, which explains the note to revisit. So this isn't just another object for astrophotographers.

  James Whinfrey - Website Administrator.

• The NGC 2264 in Monoceros

  January 2021 - Picture of the Month

  

  Is the open cluster the main feature in this image I wonder? Perhaps I've misnamed this month's article, but NGC 2264 does refer to the Cone Nebula, at the bottom of the frame, and the Christmas Tree Cluser that provides bright star at its tip.

  But that hardly covers the extent of the nebulosity here. The Fox Fur Nebula is towards the top right, and shows wonderful texture (that's much better in the version of Thomas's website). The field is full of glowing dust!

  The bright star near the centre of this image is magnitude 4.66 S (15) Monocerotis that lights up the nebula with a hint of blue reflection. Jim Kaler points out that this is actually two large stars (12 and 18 solar masses) in a close orbit of about 26 AU, so you're not going to split that. But you might like to know that it's also an uneven double with a magnitude 8.5 companion about 3" distant (STF 950 AB).

  The open cluster is easy to observe with binoculars or small telescopes, this field is about a degree across so it's not small. Unfortunately it takes a large telescope and filters to make much of that glorious nebulosity visually. However, as demonstrated here, it is a spectacular target for those with a camera.

  James Whinfrey - Website Administrator.