Six years since the discovery of comet SWAN, the sungrazer!

It was six years ago, in early March of 2012, that Ukrainian amateur astronomer Vladimir Bezugly noticed an obvious comet rapidly approaching the Sun in SOHO/SWAN images. Unlike any ordinary comet, derived orbital elements from the SWAN images revealed the comet to be a Kreutz-group sungrazer! This was interesting because no such sungrazer had ever been detected in these images, not even comet C/2011 W3 (Lovejoy), aka the Great Christmas comet of 2011! This lead to speculation that this newly discovered comet (C/2012 E2 (SWAN)) would potentially brighten into an exceptionally bright naked-eye comet!

comet swan c2SOHO/LASCO C2 image extract of Comet SWAN taken on March 14th, 2012. Image credit: ESA/NASA/NRL SOHO/LASCO C2.

On March 8th, 2012, Vladimir Bezugly posted a message on the SOHOHunters forum indicating that a bright object could be seen close to the Sun in two SOHO/SWAN images, with the speculation that it might be Kreutz-group comet, if real. Other amateurs astronomers, including Michal Kusiak (Poland) and Rob Matson (USA) quickly intervened that same day and confirmed his sightning!

With the available SWAN images at the time of discovery, Michal Kusiak derived a possible preliminary orbit in favor of a Kreutz-group sungrazer! As quoted from the SOHOhunter message, Michal’s exact words were “ I do not want to [express] excessive enthusiasm, but it looks really interesting“! As of that day, amateur and professional astronomers were following the comet closely during its inbound journey towards perihelion!

output_xilhpEComet SWAN as seen in the  SOHO/SWAN Comet tracker images, including some of the discovery frames! Notice how the comet appears rather stellar in these images, which is due to the resolution of these images. Also, one can see the comet dissapear behind the occulted region of the images on March 10th. Image credit: ESA/NASA/LATMOS SOHO/SWAN.

Despite the excitement, astronomers were cautious about estimating a peak brightness of this object, as comets can have a very unpredictable behavior. Indeed, comets can quickly flare up into beautiful and bright objects, as they may suddenly disentigrate and fade out of view! One example more recent than comet SWAN was comet C/2012 S1 (ISON), which gained lots of attention from the media, as it was speculated that it could be a “Great comet” in late-2013! Contrary to these speculations, comet ISON brightened slower than predicted, and didn’t reach more than mag -2 at perihelion, before fully disentigrating!

comet ison hi1a 20131201Enhanced STEREO/SECCHI HI1-A image exctract showing the dusty remnant of comet ISON taken three days after its perihelion. Image credit: NASA/NARL STEREO/SECCHI HI1-A.

Unfortunately, no definitve ground based observations could be obtained of this comet during its inbound journey, as the comet was unfortunately too close to the Sun. In other words, as seen from Earth, the comet was located in daylight, masked by the intense light of the Sun! I say “definitive” because amateur astronomer Terry Lovejoy (Australia) was later able locate a “stellar-looking” object in an image he took on March 10th, 2012 at about the expected location of the comet!

Only SOHO/LASCO and STEREO/SECCHI images could follow up on this object. With only the several SWAN images available, it was difficult to estimate a precise time when the comet would enter the FOV of either of those telescopes.

Despite the unpredictability of the comet’s brightness, most assumed that the comet would at least be a fainter rival comet comet Lovejoy, hence it was expected that it would be clearly detectable in the real time (low quality) STEREO/SECCHI HI1-B beacon images. Instead, it was hardly detectable in those images! In fact, these images showed the comet to be uncomparable to the brightness of comet Lovejoy. Moreover, it seemed like it would comparable to an “ordinary”, relatively bright SOHO/STEREO comet, such as SOHO-3184 or STEREO-23! This was later supported by SOHO/LASCO C3 observations when it entered the FOV on March 13th!

images/SWAN/SWAN_hi1b_SW.jpgComet SWAN as seen in the low quality STEREO/SECCHI HI1-B beacon images. Notice how the comet is poorly resolved and very faint in this image. Image credit: NASA/NRL Karl Battams STEREO/SECCHI HI1-B.

In SOHO/LASCO C3 images, there too, like observed in the real time  HI1-B images, comet SWAN was uncomparable in brightness to comet Lovejoy. It seemed no different than the rather typical bright comets occasionally observed by SOHO (on an almost-yearly basis)! Notice in the image comparison below the similarity in brightness between SOHO-3184 (a typically bright Kreutz sungrazer) and comet SWAN! Unfortunately, it didn’t seem like it would become an exceptionally bright object, or even less survive perihelion…

Due to these observations, there were speculations that the comet might have been a direct fragment from a much larger comet that fragmented while in the SWAN FOV, suggesting that this object might be followed by a storm of Kreutz-group comets! However, this was not observed to be the case. Another suggestion: Knowing that the SWAN observes in the Halpha band (unlike LASCO), it was thought that the brightness of the comet in SWAN might be due to strong Halpha emissions. However, while studying the comet in different filters in SOHO/LASCO, this was proven not to be the case either…

comparison comet swanComparison between comet SWAN (left) and SOHO-3184 (right), the latter being a relatively bright Sungrazing comet, alot fainter than comet lovejoy (and definitely not detectable in SWAN!). Notice how they are rather comparable to each other, in brightness. Image credit: NASA/NRL SOHO/LASCO C3.

output_5gznpAAnimation of SOHO/LASCO C3 image extracts showing Comet SWAN rapidly approaching perihelion. Notice how the comet brightens until the last image, where the head seems fainter and more elongated (likely the result of severe disentigration). Image credit: ESAN/NASA/NRL SOHO/LASCO C3.

On March, 14th, the comet entered the SOHO/LASCO C2 FOV (see the first image, above), and as predicted, after passing behind the SOHO/LASCO occulter, it never re-emerged… The comet was already fading before having entered SOHO/LASCO C2 images, as can be seen in the animation above.

The final moments were also observed in the  STEREO/SECCHI COR images, where the comet also appeared no different from any of the “ordinary” bright Kreutz comets occasionally observed in these images. Below is a comparison between comet Lovejoy and SWAN in COR2-B, notice the very obvious contrast in brightness!

comet swan lovejoy cor2bComparison between comet SWAN (left) and comet Lovejoy (right). Notice the very large difference in brightness between the two, comet SWAN being alot fainter! Image credit: NASA/NRL STERE/SECCHI HI1-B.

output_CjqrInAnimation of (slightly compressed) COR1-A images showing the final moments of comet SWAN. These are some of the last images ever taken of this comet. Image credit: NASA STEREO/SECCHI COR1-A.

The high-resolution HI1-B images were released just after the comet vanished. In these frames, one can clearly see the effect of the Solar wind on the tail of the comet, as can be seen in the animation below!

output_NSy9zVAnimation of comet SWAN as seen in HI1-B images. Notice the effect of the Solar wind on the tail of this comet, causing the comet to temporarily sport an apparent “forked” tail! Image credit: NASA/NRL STERE/SECCHI HI1-B.

In the end, despite comet SWAN being alot fainter than expected, it was still a rather spectacular comet! It’s not every day that the SOHO/LASCO and STEREO/SECCHI telescopes are treated to a comet of this brightness! 🙂

The reason for the comet’s unusual brightness however still remains unknown. Some speculate that the comet suffered an outburst while it was in the SOHO/SWAN FOV, or that it was a larger comet that disentigrated a few days after discovery… The answer will most likely never be known!


Bright sungrazer recently observed by STEREO!

On February 7th, 2018, amateur astronomer Zhijian Xu (China) reported a previously unknown Kreutz-group comet in images taken by the SOHO spacecraft (LASCO C3 instrument). The comet quickly brightened and was soon very prominent, perhaps only a couple/few magnitudes in brightness on 2018-02-08! In this post I discuss the comet as seen from the perspective of STEREO-A.output_MXkQVJAnimation of the comet’s final moments as seen in COR2-A. Notice how the head of the comet seems to have nearly vanished in the later frames. Image credit: NASA/NRL STEREO/SECCHI COR2-A.

In STEREO, the comet was first recovered by its discoverer in HI1 images taken on 2018-02-05. By 2018-02-07 the comet started displaying a very long and prominent tail, clearly interacting with the Solar wind (see below).  The comet exited the HI1 FOV on 2018-02-08 at 05:30 UT, but the tail persisted hours after leaving those images! In fact, the Solar wind caused significant disturbances in the comet’s tail just after it exited the HI1 FOV (see below)!

output_EndUO9output_lxMcK8Left: Animation of the comet before exiting the FOV on 2018-02-08. Notice its bright head and obvious tail. Image credit: NASA/NRL STEREO/SECCHI HI1-A.

Right: Animation of the comet’s tail in HI1-A persisting after the comet itself left the FOV. Notice how the tail suddenly appears “forked” and becomes “wavy”, these are disturbances caused by the tail’s interaction with the outflowing Solar wind. Image credit; NASA/NRL STEREO/SECCHI HI1-A.

The comet reached its peak brightness in the COR2 FOV, at some point around 15:00 UT on 2018-02-08. Past that time the comet started fading, and its head was clearly reducing in size, indicating that it was rapidly disentigrating. The last images of this “doomed” comet were taken by the COR1-A telescope on 2018-02-08 at 22:00-23:00 UT, before it passed behing the telescope’s occulter. Unsurprisingly, it was never seen to re-emerge.

output_Fem4UpThe final moments of the comet as seen from the COR1-A images. Notice how the comet’s tail persists after having passed behind the occulter. These were the last images taken of the comet. Image credit: NASA STEREO/SECCHI COR1-A

The comet appears to be a member of the Kreutz-group. These account for about 85% of all Sungrazing comets observed by SOHO. The family includes many “Great comets”, most notably C/1882 R1, C/1965 S1 (Ikeya-Seki) and C/2011 W3 (Lovejoy)!


Sungrazer Project, STEREOHunters Yahoo Forum and personal observations.

Finding stars that aren’t stars: Planetary nebulae discovered by the APO team!

The Atacama Photographic Survey (APO) is a remotely controlled observory in the Atacama desert run by French amateur astronomers Thierry Demange, Richard Galli and Thomas Petit (APO-team). Its chosen location makes it ideal to observe the wonders of the Southern Sky, with stunning images having been taken of the Carina and Prawn Nebula, among many others! However, their technique of imaging have revealed a few tens of Planetary Nebulae that otherwise mimick the appearance of ordinary stars! DeGaPe 4 finalExtract of NGC 3576 taken by the APO-team using the SHO method (SII+Halpha+OIII). The image reveals one of their discoveries: DeGaPe 4, a possible “stellar” Planetary Nebula. Notice how its flashy green colour stands out in comparison to the rest of the stars in this image! (c) APO-team.

The APO-team has been imaging the Southern sky since 2014, but it wasn’t until the beginning of 2015 that they made their first (accidental!) discovery: DeGaPe 1 (see further below). As the team started imaging using the SHO technique (combining SII, Halpha and OIII exposures), they started noticing “stars” that displayed particular fluorescent colours that clearly stood out in their images. It turns out that these objects were not stars at all, but are more likely small and/or compact Planetary Nebulae! Their distinct colours in SHO images are due to their strong OIII, Halpha and SII emissions, atypical of “ordinary” stars. Below are some examples of their “stellar” PN candidate discoveries. DeGaPe discoveriesMosaic of put together by the author of twelve stellar Planetary Nebula candidates discovered by the APO-team. Notice their unusually flashy green or blue colours in comparison to the surrounding stars. KnDeGaPe 1 was co-discovered with austrian PN hunter Matthias Kronberger. (c) APO-team.

In fact, some of their discoveires appear compact to the point that not even the high-resolution DECaLS images can display their nebulous nature! Furthermore, their Mid-IR signal doesn’t always display the “typical” colours of PNe! Hence, only SHO imagery are able to really reveal their PN-like nature. Hence, no wonder why these PN candidates were discovered only recently!DEGAPE 43DeGaPe 43: A PN-like object in APO SHO imagery (left), but that in DECaLS (middle) appears completely stellar and that displays an WISE signal atypical of most PNe! PNe in WISE tend to peak in the W4 band (will appear red in AllWISE images due to their colou-coding). Image credit: APO-team, DECaLS and AllWISE Aladin Lite. 

Unlike objects such as DeGaPe 43 (above), the rest of their finds display typical Mid-IR signals, and/or appear nebulous (at least quasi-stellar) in DECaLS. DeGaPe 6 is one such typical PN-like object!Degape 6 sho apo decalsDeGaPe 6: an PN-like object in APO SHO imagery (left), that displays a surrounding halo in DECaLS (middle) with a rather typical PN-like mid-IR signal as seen in AllWISE (right). Image credit: APO-team, DECaLS and AllWISE Aladin Lite.

As of February 2018, the team has discovered a total of 50 Planetary Nebula candidates, most of them being of stellar morphology, as seen above. The rest however display a very obvious nebulous nature. In fact their first discovery (DeGaPe 1) was a very faint and round PN candidate located at the edge of the Vela Supernova Remnant! Other of their nebulous finds include DeGaPe 2, DeGaPe 50 and DeGaPe Object 2 (see further below).DeGaPe 1Discovery image of DeGaPe 1. The image is taken in OIII+Halpha and shows the object to have an asymetric round appearance, appearing mostly visible in the OIII filter. (c) APO-team.

One of their more interesting nebulous finds is DeGaPe Object 2. Located in Ara. It’s a possible vast (about 8′-9′) HII candidate with a rather chaotic morphology. Its appearance is similar to many Supernova Remnants (which is what it was first thought it could be!). DeGaPe Object 2Zoomed view on DeGaPe Object 2, imaged by the APO-team using the SHO method. Notice its rather chaotic and aymetric nature. (c) APO-team.

More about the APO-team, their observatory and their finds can be found on their website;

Their wevsite also includes the full-scale images that they take, wether it be in SHO, Halpha+OIII or LRGB!


Petit, T. (2018) Atacama Photographic Survey, Available at:

Acker A. (2016) ‘LES NEBULEUSES HISTOIRE D’UNE COOPERATION’, Astronomie, February, 2016, pp. 26-32.


Nova Muscae 2018, the story!

On January 14th, 2018, when imaging around the Carina constelation, amateur astronomer Rob Kaufman (Australia) discovered a bright new Nova that had gone missed by professional surveys! Now known as Nova Muscae 2018, it is the only Nova to have been recorded in the Musca constellation since 1983!

NMus2018 widefield, 16 Jan 2018 textDiscovery image of Nova Muscae 2018. At this large scale it seems nothing more but a faint star among a million others! (c) Rob Kaufman

On the night of January 14th, 2018, amateur astronomer Rob Kaufman  decided to image comet C/2016 R2 (PanSTARRS) from his home in Bright (Victoria, Australia). His equipment consists of a Canon DSLR (EOS 650D) together with a 55mm F/5.6 lens. For star tracking he uses a Vixen Polarie monture.

When finished tracking C/2016 R2, he decided he would image the area surrounding the Carina constellation, perhaps with the second thought of discovering a new Nova. Hence, he was surprised when he noticed a bright (mag +7) star that was nowhere to be seen in his older images! Being a dedicated Nova hunter since 2010, Rob knew that one must be cautious with such objects. Indeed, one has to be sure that an apparent Nova is not the result of a Minor planet or any other kind of variable star (Mira stars or Eclipsing Binaries for example). Not to mention one must make sure that the transient is unreported!

PNV J11261220-6531086, 14 Jan 2018 crop textCropped version of the discovery image (above), showing Nova Muscae 2018 as a very obvious object! (c) Rob Kaufman

As he gradually worked through the required checks above, he realized what he had found was most likely a Nova, and neither of the “false alarms” mentioned previously. Hence, he finally he decided to prepare a discovery report for the Central Bureau for Astronomical Telegrams (CBAT). As he was preparing the report, he could still not believe his find, as it seemed too good to be true. Then just before submitting his report, he realized his find was bright enough to obtain a low-resolution spectra! Hence he brought back out his equipment to obtain the results below! His spectra indicated the transient to have evident Hydrogen emission. This confirmed his find to indeed be a true Nova! The simultaneously presence of Fe-II lines in the spectra indicated that the transient was more precisely a classical FeII nova. With this information now in hand, he finally posted his report to the CBAT. It soon  recieved a primary designation as PNV J11261220-6531086, and later it was given its second designation as Nova Musca 2018.

PNV J11261220-6531086 spectrum, 14 Jan 2018 textSpectrum of Nova Musca 2018 as taken by Rob Kaufman soon after discovery. These results confirmed his object to indeed be a Nova! (c) Rob Kaufman.

It didn’t take long before other astronomers started getting involved with Rob’s find. Robert Fidrich (Hungary) was the first to take confirmations of the object, using the T13 telescope at the iTelescope network. With Rob’s and Robert’s images, Daniel Bamberger (Germany) and Patrick Schmeer (Germany) were able to determine some more precise coordinates for the transient.

Daniel was also able to recover the nova in data from the All Sky Automated Survey for SuperNovae (ASAS-SN). This showed the eruption to have initiated almost a couple weeks earlier, between January 1st and 3rd. On January 3rd ASAS-SN indicated the Nova to be around mag +8.8. This indicated that the transient to still be brightening.

light_curve_87fd7dc5-af64-42aa-9f2e-59b05de938f9Preliminary lightcurve obtained by the ASAS-SN. These earliest magnitude measurments of Nova Musca 2018. As one can see, the eruption started between MJD 4 and 6 (Jan 1 and 3). Image credit: ASAS-SN Sky Patrol (Shappee et al. 2014ApJ…788…48S and Kochanek et al. 2017PASP..129j4502K).

AAVSO data collected by many observers over the course of the Eruption shows the Nova to have reached a maximum magnitude close to Vmag +6.5 on January 15th, and has been slowly fading ever since. At the time of the submission of this post, the Nova seems to be around mag +8 (see AAVSO lightcurve below). Hence, the Nova just grazed naked-eye visibility in mid-January! Furthermore, one report indicates a positive naked-eye detection of the transient under very good sky conditions!

aavso nova musca 2018

AAVSO light curve (Johnson V magnitude and Visual measurments) of Nova Musca 2018 (updated January 28th, 2018) since its maximum on January 15th, 2018. Notice it’s slow and linear fading. This lightcurve is the based on measurments taken by many astronomers and AAVSO contributors world wide. Image credit: The Amarican Association of Variable star observers (AAVSO).

The following (via the link below) GIF animation put together by Ernesto Guido (Italy) shows the comparison of Nova 2018 Muscae before its eruption and at it’s brightest! The former image is a DSS plate taken in 1998, while the latter is an image taken by Ernesto Guido and Alfonso Noschese on January 15th. In their image they estimated the nova to be close to mag +6.3.

Copy link:


AAVSO VSX Sebastian Otero (2018) Nova mus 2018, Available at: (Accessed: 28th January 2018).

CBAT Various (2018) CBAT PNV J11261220-6531086, Available at: (Accessed: 28th January 2018).

Private communication/mails with Rob Kaufman.

Solar Observatories observe the demise of a bright Sungrazer and its many fragments!

On December 21st, both the Solar Heliospheric Observatory (SOHO) and the Solar Terrestrial Relations Observatory Ahead (STEREO-A) observed the demise of a bright Sungrazing comet, presumably a Kreutz-group member! Moreover, the comet was accompanied by four small fragments, all which vanished along with this bright comet.

output_zJVm5eAnimation of the bright new Sungrazing comet, and its four tiny fragments (marked by the black lines)!  These were some the last images of these comets before their demise. Image credit: ESA/NASA SOHO/LASCO C2.

The bright comet was discovered in the publically available SOHO/LASCO C3 images on December 19th, by Polish amateur astronomer Szymon Liwo. At the time the discovery images were taken the comet was still very faint, but it quickly brightned over the next couple of days to become a magnificient object!

comet 20171219 discoveryExtract of one of the discovery SOHO/LASCO C3 images of the bright comet (circled). Notice the dense starfield of the Milky Way in the background! Image credit: ESA/NASA SOHO/LASCO C3.

Only several hours before the comet’s demise, Masanori Uchina (Japan) and Worachate Boonplod (Thailand) reported three faint surrounding fragments in SOHO/LASCO C3 and C2 images. The 4th one was reported by yours truly a day later, in SOHO/LASCO C2 images, after having spotted it in STEREO/SECCHI HI1-A frames. However, all fragments appeared best in the SOHO/LASCO C2 images (see animation above).

output_Dx83P8Animation of all 5 comets in STEREO/SECCHI HI1-A diff images. All the four faint fragments are marked by the red lines. One of them is only partially distinguishable from the bright comet. The first one to leave the Field-of-view was discovered in these images. Notice the intense solar outflow entering the FOV. Image credit: NASA/NRL STEREO/SECCHI HI1-A.

All five comets were visible in STEREO/SECCHI HI1-A images. Personally, I found some of them difficult to spot in those images, but they were definitely all there! The comet I reported was perhaps the most difficult to observe (as its clearly the faintest of them all). When I first found it in STEREO, I thought it was one of the previously known 3 fragments, until I noticed those were located elsewhere in these images! I wasn’t convinced by its appearance in STEREO, so I searched for it in SOHO/LASCO C2 images, where it definitely appeared. Hence I reported it in those images.

More than being used to recover all of the four fragments, the STEREO gave us a stunning view of the bright comet. In these images, not only did we observe a long tail (like in SOHO/LASCO), but the tail dynamics were very obvious (see animation below). This is caused by the interaction between the comet and the intense Solar wind.

2017_12_20_kreutz_HI1AAnimation of the bright comet as seen in STEREO’s HI1-A images. Notice how the Solar wind interacts with the comet’s tail, causing it to continuosly move! Notice how some of the fragments are also apparent in these images. Image credit: NASA/NRL STEREO/SECCHI HI1-A.

Like SOHO/LASCO C2, the STEREO/SECCHI CO2-A telescope also captured the comet’s very last moments. Below is an animation of the comet’s diesntigration as seen in these images. The small fragments were too faint to appear in these images.

output_pMOgXZAnimation of four COR2-A frames showing the demise of the bright comet. Image credit: NASA STEREO/SECCHI COR2-A.

The comets are most likely members of the Kreutz-group, a vast family of comets resulting from the continuous fragmentation of a bright sungrazing comet observed millenniums ago. These account for about 85% of all Sungrazing comets observed by SOHO. The family includes many “Great comets”, most notably C/1882 R1, C/1965 S1 (Ikeya-Seki) and C/2011 W3 (Lovejoy)!

More unknown Nebulae discovered by amateurs online!

Using the publically available images online, such as the Digitalized Sky Survey (DSS) and the Pan-STARRS1 dataset, amateurs have continued to spot previously unknown nebulae that have yet to be catalogued! In this post, I feature Mo Object 2, Pre Object 3, Su Object 1 and Su Object 2. Most, if not all, of these objects are likely somewhat associated with Star forming regions. The nebulae were all found when hunting specifically for Planetary Nebula candidates.

newer nebulae amateursDSS2 and Pan-STARRS1 extracts of Mo Object 2, Pre Object 3, Su Object 1 and Su Object 2. Image credit: DSS2 and the Pan-STARRS1 Science Consortium.

Mo Object 2: A beautiful Reflection Nebula in Auriga, discovered by Sankalp Mohan (India) in the Mid-IR WISE images, in September. The nebula seems to be associated with a small and obscured star forming region.  The object is located within the Auriga Star forming region, rich in many such nebulae, as can be seen in the area surrounding IC 417, also a member of the Auriga Star forming region.

IC 417DSS2 image extract of IC 417, a vast emission nebula assoctiated with a massive star forming region. One can notice many surrounding reflection nebulae (blue nebulosity), similar to Mo Object 2. Image credit: DSS2

Pre Object 3: Accidental find when trying to recover Pre Object 2 in Pan-STARRS1 data. It was found by Trygve Prestgard (France) and appears to be a cometary globule. It was found only minutes after having first spotted Pre Object 2, in September, 2017.  This nebula is located in a area rich in active star formation, hence many cometary globules.

Pre object 2 and 3Pan-STARRS1 image extract showing Pre Object 3 (upper left) and Pre Object 2 (low right). Pre Object 3 was found in these images when trying to recover Pre Object 2. Image credit: Pan-STARRS1 Science Consrtium.

Su Object 1: This is a nice fan-shaped nebulosity in Auriga, appearing strongly in Optical Red images. The nebula was found by Guyou Sun (China) in October, 2017, using the DSS2 and Pan-STARRS1 images.

Su Object 2: Another find by Guyou Sun, this is an obvious nebulosity in Cassiopeia. The object is located in an area rich in star formation, with many other interesting nebula nearby. This includes reflection nebulae such as LBN 590 and emission nebula associated to HII regions such as NGC 7822.

LBN 590 and NGC 7822DSS2 image extracts of reflection nebula LBN 590 and star forming region NGC 7822. The latter is actually zoomed-in on a only a portion of the NGC 7822 region, known as the Elephant Trunks, which are vast pillars of star formation. Image credit: DSS2

The hunt for unknown nebulae online continues, available to anyone with an internet connection, spare time and lots of patience! Publically available data, even as old as 50 years, still hide many unknown nebulae wating to be discovered!


IC 4628 and the land of a thousand Planetary Nebulae!

IC 4628, also known as the Prawn Nebula, is a vast emission nebula in Scorpius. Its large apparent size and its brightness makes it a popular target among astrophotographers in the Southern Hemisphere. Despite having been known for well over a century, it’s only over the past decade (especially these last few years!) that astronomers realized that many small (stellar) Planetary Nebulae lie within its vicinity. Most having been found by amateur astronomers!

prawnAllWISE image extract of IC 4628 and some its neighbouring Planetary Nebulae.  Image credit: Aladin Lite.

Planetary Nebulae candidates DeGaPeKn 1 and 2 were discovered independently by Matthias Kronberger (Austria) and the APO team from France (made up of Thierry Demange, Richard Galli and Thomas Petit). Matthias found the nebulae in mid-IR data from WISE and from Halpha images of the MASH project. The APO team discovered them in their narrow-band SII-OIII-Halpha images of IC4628.

Pre 11 was discovered by Trygve Prestgard (France) in 2016 when re-inspecting the APO team’s narrow band images and the WISE data of the area. The nebula is partially obscured by the nebulosity of IC 4628, making it slightly more difficult to observe. The MASH images of the area were highly contaminated by IC 4628.

Mo 5 was discovered most recently by Sankalp Mohan (India) using the available WISE data. It’s optical brightness is similar to DeGaPeKn 1 and 2, but its Halpha emissions as seen in MASH images are less pronounced.

The two remaining nebulae were discovered by the MASH team a few years before the amateur finds.

Faint Sungrazer twins vanish together!

On November 25th, 2017 two faint sungrazing comets were seen plunging towards the Sun together. Like most small sungrazers, these did not survive their solar encounter. In fact, they most likely vanished before reaching perihelion! The comets were of unequal brightness; the fainter comet leading the brighter one by only half an hour!

twin comets 2017 11 25Strongly cropped and contrasted SOHO/LASCO C2 image extract showing both comets. The brighter one shows hints of a tail, while the faint leading fragment simply appears fuzzy. These are what most sungrazing comets look like in SOHO/LASCO. Image credit: ESA/NASA SOHO/LASCO C2.

Both comets were discovered by Worachate Boonplod (Thailand) via the Sungrazer Project. He found the brighter companion in SOHO/LASCO C3 images of 2017-11-24 (see below). 12 hours later he reported the fainter fragment in SOHO/LASCO C2 images. It’s possible, if not likely, that these fragments split from each other very recently, maybe only decades ago?

Faint sugrazing comets like these represent the majority of comets observed by the SOHO/LASCO coronagraph. Most of these are detected by highly dedicated amateur astronomers via the Sungrazer Project, who spend countless hours scanning the latest SOHO/LASCO images in search for these objects.

soho twin 2017 11 25Image extract of one of the discovery SOHO/LASCO C3 image of the brighter component. The fainter leading fragment is too faint to be readibly visible in this image. Image credit: ESA/NASA SOHO/LASCO C3.

The two comets are most likely a members of the Kreutz-group, a vast family of comets resulting from the fragmentation of a bright sungrazing comet observed millenniums ago. These two comets clearly indicate the fragmentation among Kreutz-group comets is still an ongoing process!

The 2017 return of 96P/Machholz, what did we see?

On October 27th, 2017 comet 96P/Machholz reached its 6th Perihelion passage since it’s discovery in 1986. At the time Don Machholz discovered this comet it had already passed perihelion. 96P/Machholz is a rather unusual comet, in the case of its composition (reltaively low in C2, C3 and Cyanogen) and unusual orbit for a short periodic comet (very inclinated and eccentric).

In this (unusually long) post I will go into some depth regarding the inbound journey and  perihelion passage of 96P/Machholz as seen by the Solar and Heliospheric Observatory (SOHO), Solar TErrestrial RElations Observatory Ahead (STEREO-A) and by  some ground-based observations.

Nota bene: This is an updated version of a Blog post published on this website during the beginning of November.

Ground-based Observations

Before perihelion, the comet was only visible from the Southern-Hempisphere, quickly moving North and rapidly brightening. The comet wasn’t observable for very long, as it stayed extremely faint until about a month before perihelion.  Soon, by mid-October, it entered daylight as seen from Earth.

96P Machholz mattiazzoComet 96P/Machholz imaged by on October 2nd with C11 at f/6.3 + QHY 163m ccd. The comet was estimated to be about mag +15 in this image. (c) Michael Mattiazzo.

Michael Mattiazzo’s (Australia) magnitude measurments from October 8th to October 16th are listed below. Also, on October 2nd he estimated the comet to be about +15 mag. Rob Kauffman (Australia) estimated it to be around +13 mag on October 10th, well in accordance well Michael’s measurments.

Photometric and astronomic measurments of 96P/Machholz by Michael Mattiazzo. Notice the rapid brightening of this object as it rapidly moves towards perihelion.

Date/time UT    Coordinates (J2000.0)   Mag

2017 10 08.41448 13 40 26.50 -44 35 56.9 13.6 N
2017 10 09.42241 13 39 50.58 -43 43 17.8 13.0 N
2017 10 14.41992 13 36 19.45 -38 40 51.7 12.1 N
2017 10 15.41653 13 35 30.95 -37 24 39.3 11.2 N
2017 10 16.41198 13 34 41.12 -36 06 42.9 10.7 N


SOHO/SWAN Observations

Days later the comet was already close to +11 mag, and was hence detectable in SOHO’s  SWAN images. In these images it was possible to follow up on the brightening, as the object had passed within the Daylight zone as seen from Earth.  By late October the comet passed behind the “Sun-Occulted zone”, meant to block out the intense Ultraviolet sunlight from saturating the SWAN images.

96P Machholz swanSOHO/SWAN image extracts showing 96P/Machholz brightening as it was approaching the Sun (behind the blacked-out zone). Image credit: ESA/NASA/LATMOS SOHO/SWAN

STEREO HI1-A Observations

At about the same time the comet was passing behind the occulter in SWAN images, on October 23rd, it entered the FOV of the STEREO/SECCHI HI1-A imager. In these images the comet was bright. It was also showing a long (several degrees, and growing) prominent tail. Consequently, by the time the comet had left the FOV on October 24th, the tail was still visible after many hours. Furthermore, one could clearly see the impact of the Solar wind on the comet’s tail, causing it to appear discontinous and curvy.

96P Machholz hi1aComet 96P/Machholz entering STEREO’s HI1-A FOV (October 23rd) and the comet on October 25th when it had already left the FOV. Notice how the tail still persists almost a day after the comet left the FOV! Furthermore, notice the tail’s discontinous and curvy nature, caused by its interaction with the Solar Wind. Image credit: NASA STEREO/SECCHI HI1-A.

SOHO/LASCO observations

On october 25th, only a couple of days before perihelion, the comet entered the SOHO LASCO C3 images. Based on these images the comet appeared close to mag +2. It kept at about this brightness during its passage in SOHO/LASCO. The comet left the SOHO/LASCO C3 FOV on October 29th. In these images it was possible to distinguish two tails.

96P Machholz C3Composite image extract showing comet 96P/Machholz’s at different times when transiting the SOHO/LASCO C3 FOV. Image credit: ESA/NASA SOHO/LASCO C3

Between October 27th and 29th, amateurs reported three faint fragments leading the comet in SOHO/LASCO C3 images. Two of them correspond to 96P/Machholz-B and 96P/Machholz-C, discovered during the comet’s passage in SOHO/LASCO in 2012. The third fragment is a new discovery. The comet’s were solely observed by SOHO, not even STEREO/SECCHI images could detect them.

thumbnail_fragments.jpgSOHO/LASCO C3 (long-exposure) extract showing 96P/machholz and its three faint leading fragments. Two of them correspond to 96P/Machholz-B and C, discovered in 2012. The third one is a previously unknown fragment. Image credit: ESA/NASA/NRL Karl Battams.

Fragmentation events are nothing new to this comet. In fact, it’s likely that the precursors of the Marsden and Kracht-I comet groups were chunks that broke off from 96P/Machholz somewhere around 1000 years ago.

marsden group comet in c2An example of a bright Marsden group comet as seen in a SOHO/LASCO C2 image extract. This comet is possibly a piece of a much a larger chunk that broke off from 96P/Machholz a millenium ago. Image credit: ESA/NASA SOHO/LASCO C2.


STEREO COR-A Observations

On October 26th comet Machholz entered the STEREO/SECCHI COR2 FOV. In these images the comet was a prominent object. At its best it appeared to be around mag +2 and showed a long and prominent tail. The comet left the FOV on October 28th.

96P Machholz COR2STEREO COR2-A image extracts showing Comet 96P/Machholz before perihelion and after. Notice the prominent nature of this object in these images. Image credit: NASA STEREO/SECCHI COR2-A.

The comet also rapidly transited the COR1-A FOV on October 27th, near perihelion. Unfortunately the comet was hardly detectable in these images, as the it was practically on the other side of the Sun as seen from STEREO-A.

96P Machholz COR1STEREO COR1-A image extract showing 96P/Machholz. In these images the comet was hardly detectable, this image is perhaps one of the better COR1-A images of it. Image credit: NASA STEREO/SECCHI COR1-A.


According to Alan Hale (USA), the comet is expected to stay unobservable from the ground until about February 2018, when the comet will start entering the night sky again. By then unfortunately the comet will have become very faint. Luckily, until then, the SOHO/SWAN images has a good view of the comet. The comet reappeared in SWAN during the beginning of November, appearing bright but fading, while heading Eastward.

96P machholz swan post perihelionSOHO/SWAN image extract of 96P/Machholz only days after it reappeared from behind the occulter. Despite the low resolution of the images, a faint tail is still apparent. Image credit: ESA/NASA/LATMOS SOHO/SWAN.



I wish to thank Charles Bell, Alan Hale, Michael Mattiazzo and Ian Musgrave for the information they provided to help write (and correct) this post!

Today was the demise of a relatively bright Sungrazing comet!

Today, the Solar and Heliospheric Observatory (SOHO) witnessed the death of a relatively bright Sungrazing comet. Despite this being the case of all ~3400 comets discovered by SOHO, only a small fraction of these were as bright as this one!

bright comet octoberAn image extract showing the comet only hours before it vanished. The comet had already started to fade several hours before this image was taken. Image credit: ESA/NASA SOHO/LASCO C2.

The comet was discovered on 2017-10-13 by amateur astronomers Hanjie Tan (China) and Worachate Boonplod (Thailand) in the real time SOHO/LASCO images online. When it first found, the comet was still very faint, but it brightenened nicely as it kept approaching the Sun. Around 2017-10-13 20:00 UT the comet started rapidly fading.

soho lasco discovery image rel br cometOne of the comet’s discovery images. Image credit: ESA/NASA SOHO/LASCO C3

The comet appears to be a member of the Kreutz-group. These account for about 85% of all Sungrazing comets observed by SOHO. The family includes many “Great comets”, most notably C/1882 R1, C/1965 S1 (Ikeya-Seki) and C/2011 W3 (Lovejoy)!