STEREO spacecraft discovers its 100th comet, and many others!

On January 25th, 2018, Masanori Uchina (Japan) reported a small Kreutz-group comet in images from the STEREO-A spacecraft (see animation below). Not only was this Masanori’s first STEREO comet discovery, but it also coincidentally turned out to be STEREO’s 100th find! Masanori discovered his second STEREO comet only 17 days later, on February 9th, 2018 (STEREO-105)! STEREO-100 and STEREO-105 were both only two comets of a total of twenty-two recorded Kreutz-group sungrazing comets between January and mid-February 2018. Note that eight of them were observed over a period of only ten days, these all having been found (and solely observed) by STEREO!

output_waJXBcCropped animation of enhanced STEREO/SECCHI HI1-A images showing STEREO-100. Notice how this fuzzy comet brightens as it exits the animation (FOV). These were the last images of the comet before it disentigrated. Image credit: NASA/NRL STEREO/SECCHI HI1-A


STEREO-100: The story behind its discovery

Masanori Uchina spotted this comet on January 25th, 2018 when hunting the near-real time STEREO/SECCHI HI1-A images for Kreutz-group comets. Indeed, between November 2017 and March 2018 the STEREO-A spacecraft was well placed in space to observe the “Kreutz-group stream”, some coin this period the “[STEREO] Kreutz season”. Note that STEREO/SECCHI data is not quite real time (unlike SOHO/LASCO), as it takes a longer time to downlink the data from the spacecraft (2-3 days in average), hence the term “near-real time”. Indeed, Masanori found this comet in images taken on January 23rd. He reported his discovery to the STEREOHunters Yahoo Group forum shortly after spotting the comet (see his report below).

STEREO 100 report

Original report for STEREO-100 and my (unofficial) confirmation message posted some moments later. The official confirmation was done after the end of the “STEREO Kreutz season” in April 2018 by Karl Battams (USA NRL). Image credit: STEREOHunters Yahoo chat group forum.

Consequently, as STEREO/SECCHI data is not real time, this means that one must make sure that any possible “new” STEREO comets haven’t first been spotted in SOHO/LASCO. Luckily there were no prior mentions of any Kreutz-group comets that alligned with Masanori’s discovery, hence his find was a definite “STEREO discovery”! The comet most likely went unnoticed in SOHO/LASCO due to its apparent faintness and due to the SOHO/LASCO occulting pylon (see further below for more details).

Like all small Kreutz-group sungrazers, STEREO-100 most likely disentigrated before reaching perihelion. I say “most likely” as there are no actual images showing the comet disentigrating (even though it’s obvious in the case of such small comets). In fact, the last (and only) images of this comet show it to still be brightening! (see animation of STEREO-100 above). This is because the STEREO/SECCHI HI instruments do not observe the Sun and its immediate surroundings. In fact, the FOV focuses on the Solar Outflow beyond  a 15° offset from the Sun. Kreutz-group comets in average start disentigrating at about 10° (I think…). Hence, it’s the SOHO/LASCO and STEREO/SECCHI COR telescopes that usually get to observe the disentigration. However, as mentioned, STEREO-100 was too faint be observed by SOHO, thus making it even less likely to have been observed by the COR telescopes! Indeed, COR is poorly sensitive to comets, only brighter ones (that already appear obvious in SOHO) can be detected in these (see COR2-A animation of SOHO-3492 further below).

output_laVUlACropped animation of enhanced SOHO/LASCO C2 images showing the disentigration Kreutz-group comet SOHO-2465. These were the last images of the comet. Image credit: ESA/NASA/NRL SOHO/LASCO C2.

On April 16th, 2018, long after the “STEREO Kreutz season” was over, Karl Battams posted the official confirmations of the most recent STEREO comets, in which he stated that Masanori’s comet was STEREO’s 100th comet discovery! “Many congratulations to Masanori for finding STEREO’s 100th comet!“.


Backstory: STEREO’s comets

STEREO’s 100th comet discovery is the result of eleven years of intense scrutinizing of the STEREO/SECCHI images, by both professional and amateur astronomers. The first ever STEREO comet discovery was made by amateur astronomer Alan Watson (Australia) in STEREO/SECCHI HI1-B images of 2007-08-31 and 2007-09-01. The comet is unintuitively designated STEREO-65.

stereo 65STEREO-65 as seen in a strongly cropped STEREO/SECCHI HI1-B image from 2007-09-01. This was one of the last (and only) images of this comet. It was most likely too faint to be recovered in SOHO/LASCO. Image credit: NASA/NRL STEREO/SECCHI HI1-B.

This small Kreutz-group comet appeared very similar to STEREO-100, and was only officially confirmed a couple years ago, when re-inspecting the HI1-B images (hence its designation). At the time of its discovery, astronomers were still getting to know and “figuring out” STEREO/SECCHI. Consequently, because of the comet’s faintness, there was not enough evidence to support its existence (especially as the processing methods used back then were less adapted to the data). The first confirmed STEREO comet find, STEREO-1, was discovered quite a bit later, on 2008-02-19 (also by Alan Watson)! STEREO-1 was followed by STEREO-2, STEREO-3 and STEREO-4 only days later! All these four comets were of the Kreutz-group, like about 95% of STEREO’s comets! The remaining 5% are non-group comets, like STEREO-61 and STEREO-88 (see images below).

soulier C2014 C2Comet STEREO-61 imaged on 2014-03-02. (c) Jean-François Soulier

output_7GBRe9Animation of comet STEREO-88 in STEREO/SECCHI HI1-A images arcing around the Sun. The comet is seen in the upper-left quadrant of these images. These were the last images of this comet. Image credit: NASA/NRL STEREO/SECCHI HI1-A.


January 2018: A flurry of faint Kreutz-group sungrazing comets!

As mentioned previously, STEREO-100 was far from being the only STEREO comet discovery of 2018. In fact, a total of fourteen Kreutz-group STEREO comets were discovered between January 6th and February 9th, with eight of these (including STEREO-100) having appeared between January 13th and January 23rd! Below are animations of a couple comets that appeared during this mild “comet storm”. As one can see in these GIFs, the comets were indeed faint. It is mainly due to this reason that they went unnoticed SOHO/LASCO.

output_I1pw3RCropped animation of enhanced STEREO/SECCHI HI1-A images showing STEREO-94. These were the last images of the comet before it disentigrated. Image credit: NASA/NRL STEREO/SECCHI HI1-A

output_UYsCmwCropped animation of enhanced STEREO/SECCHI HI1-A images showing STEREO-96. These were the last images of the comet before it disentigrated. Image credit: NASA/NRL STEREO/SECCHI HI1-A

A couple weeks after this small flurry of Kreutz-group sungrazers, a very bright comet (about mag +2) of the same family transited the STEREO/SECCHI and SOHO/LASCO FOVs. More about this comet (SOHO-3492) can be found in a previous blog post I wrote back in February:

output_MXkQVJThe bright Kreutz-group comet SOHO-3492 as seen in STEREO/SECCHI COR2-A images of February 9th, 2018. Image credit: NASA/NRL STEREO/SECCHI COR2-A.Note that


January 2018: Why did STEREO suddenly discover so many Kreutz-group comets?

Interestingly, despite a similar number of Kreutz comets having been observed in December 2017 and January 2018, the proportion of these found either and SOHO or STEREO vary drastically! Indeed, only 13% of the 17 Kreutz comets observed in December were discovered in STEREO images. However, this proportion increased  to 75% in January!

December 2017 January 2018
SOHO Kreutz-group comets 15 4
STEREO Kreutz-group comets 2 12
Total  17 16

Table displaying the number of Kreutz-group comets discovered individually by SOHO and STEREO during December 2017 and January 2018.

This sudden and drastic increase of the STEREO discovery rate has nothing to do with the location or properties of the STEREO spacecraft. In fact, it is an effect almost enterily related to SOHO! The reason starts with the geometry of the Kreutz-group comet stream as seen from SOHO during December and January. Over the course of the year, as SOHO orbits the Sun, it observes the “Kreutz stream” from different angles, meaning that the geometry of the trajectories of Kreutz comets over the course of the year changes as seen from SOHO. These changes are already obvious from one month to another. In the case of December to January, the “Kreutz stream” moves East in the sky, further away from the SOHO/LASCO C2 FOV (see the schematic representation below). This impacts the amount of comets observed by SOHO, as the SOHO/LASCO C3 FOV has a much lower resolution than C2. Indeed, practically all Kreutz-group comet discovered in SOHO/LASCO in December are found in C2! This is because most Kreutz comets are infact too faint to show up in C3, due to the telescope’s resolution.  On top of all that, the Kreutz stream in January was mostly masked by the Occulting pylon (the device holding up the SOHO/LASCO Coronagraph). Unlike SOHO, the apparent geometry of the Kreutz stream as seen from STEREO practically didn’t change between December and January, hence it had a very good view of the comets that SOHO was missing out on! Especially as the STEREO/SECCHI HI1-A images can observe comets just as faint as those solely visible in C2!

Kreutz comets december januarySchematic representation of the trajectory of typical Kreutz-group comets as seen in SOHO/LASCO from mid-December to mid-January. The length of the curves correspond to the part of the trajectory in which the comet are usually detectable.  Notice how Kreutz-group comets observed in December [generally] survive long enough to appear in the SOHO/LASCO C2 FOV. In contrast, those observed in January rarely make it into the C2 FOV. Furthermore, notice how the trajectory of the January Kreutz comets are alot more obscured by the pylon, in comparison to the December comets. Image credit: ESA/NASA SOHO/LASCO and Trygve Prestgard.

With the reasons above, this explains why comets such as STEREO-100 went undetected by SOHO/LASCO in January, while comets of similar brightness such as SOHO-3481 and SOHO-3483 were first found and best seen in SOHO/LASCO*. Note that the latter two comets were only visible in HI1-A and C2 (see animations below).

output_s2BIxzCropped animation of enhanced STEREO/SECCHI HI1-A images showing SOHO-3478, SOHO-3481, SOHO-3483. Despite these comets being just as bright the STEREO comets of January 2018, they better appeared in SOHO/LASCO! Image credit: NASA/NRL STEREO/SECCHI HI1-A


Animation of the bright Kreutz-group sungrazing comet SOHO-3478, and its four tiny fragments (marked by the black lines, in the floowing order): SOHO-3483, SOHO-3481, SOHO-3479 and SOHO-3480. These were some the last images of these comets before their demise. Had these comets appeared only a couple weeks later, it would have been unlikely that the four fragments would have been detected by SOHO at all! They would most likely solely have appeared in STEREO, similarly to STEREO-100.


*Note that I actually first discovered SOHO-3483 in STEREO/SECCHI HI1-A images of 2018-12-20 before reporting it in SOHO/LASCO C2. This is because I was very unsure about its appearance in STEREO. It appeared better in C2 images, hence it was easier to report it using those observations. More about this comet and it’s fragments can be found in this old blog post I wrote back in December 2017:


Newly discovered Planetary Nebula candidates by amateurs!

Now with more amateur astronomers being equipped with larger instruments, along with the increasing amount of High-resolution survey data being released to the public online (SDSS, Pan-STARRS; DECaPS, etc), amateurs are playing an important role in the total number of discovered Planetary Nebulae!

Below are just some of the numerous Planetary Nebulae that were discovered in late 2017 and early 2018 by amateur astronomers. These do not include the discoveries made by the Deep Sky Hunters group (they deserve a blog post of their own! ) Anyways, this blog post is already  longer than usual! 🙂

As can be seen when looking at these discoveries, it’s obvious that there are still many beautiful Planetary Nebulae still waiting to be discovered!

CaVa 1 – Vast and complex circular Planetary Nebula

This is a beautiful circular Planetary Nebula discovered by Jean-Paul Cales et Michael Vanhuysse (France) in an Halpha image they took via their observatory in Nerpio (Spain). The nebula has a large apparent size, almost 7′ in diameter! Its morphology is almost completely circular, displaying internal heterogeneities. The nebula is also very obvious in IPHAS survey data, and also faintly detectable in images from the Digitalized Sky Survey and Pan-STARRS1. Pascal Le Dû (France) confirmed the object to be a true Planetary Nebula via his own spectroscopic observations.

CaVa1 stephane zollImage extract of CaVa 1 as imaged by Stephane Zoll (France). The image is a combination of an Halpha and OIII exposure, colour-coded red and blue respectively. Notice how the nebula almost appears as a complete (heterogeneous) disk. (c) Stephane Zoll.

CaVa1 iphas halphaIPHAS Halpha Image extract partially showing CaVa 1. In these images too the nebula is very circular, displaying an inner “bar” structure dividing the nebula in two nearly-equal halves! Image credit: IPHAS Halpha

CaVa_dssredDSS Image extract showing *very faintly* CaVa 1. In these images only the most enhaced parts of this PN appear. One can partially see the nebula as a very faint arc covering the lower and lower-right part of this image.


Su 1 – Bipolar Planetary Nebula candidate with no optical counterpart

Guyou Sun (China) discovered this very strange nebula in images from the WISE satellite, where the object displayed a Mid-Infrared signal typical of a Planetary Nebula. Atypical of Planetary Nebulae however, Su 1 appears best in the Near-Infrared,  where PNe usually appear the faintest! Furthermore, the nebula doesn’t seem to appear in optical images at all. The nebula displays a remarkable bipolar nature, especially as seen in Pan-STARRS1 images. Su 1 is also faintly apparent in Infrared images from the Digitalized Sky Survey.

Su 1 ps1Pan-STARRS1 image extract showing Su 1. Notice the object’s very obvious bipolar nature, stemming from a bright Near-Infrared central object. The object lacks an optical counterpart in Pan-STARRS1, which is very atypical of Planetary Nebulae! Image credit: Pan-STARRS1 Science Consortium

dss2ir su 1Su 1 as seen in a Near-Infrared DSS frame. The lines mark the center of the object, and is quasi-perpendicular to the orientation of the bipolar nebula (faintly visible). Image credit: DSS Plate Finder.


Tan 2 – Possible condensed elliptical Planetary Nebula

This is a small Planetary Nebula candidate discovered by Hanie Tan (China) using survey images from the WISE satellite, the Digitalized Sky Survey (DSS), SuperCosmos Halpha Sky Survey (SHS) and Pan-STARRS1. The object was first flagged as an emission-star but Pan-STARR1 clearly indicated the object to be a nebula, with the morphology and colours typical of a Planetary Nebula! The SHS images also seem to faintly reveal the object’s non-stellar nature.

Tan2ps1Pan-STARRS1 image extract showing Tan 2 as an obvious compact elliptical nebula. It’s green colorimetry in these images is typical of Planetary Nebulae. Image credit: Pan-STARRS1 Science Consortium.

Tan2 shsSHS Image comparison showing Tan 2. Notice the object’s non-stellar nature, as well as its very strong Halpha signal, typical of Planetary Nebulae. Image credit: SuperCosmos Halpha Sky Survey.


St 4 – Possible quasi-stellar Planetary Nebula

This is a small compact Planetary Nebula candidate discovered by Xavier Strottner (France) online using the Digitalized Sky Survey Plates (DSS). In these images, the object appears best in the optical plates, rather than in the Infrared DSS images (which is a good sign of a Planetary Nebula!). Despite the object apearing alot more disk-like (with a central condensation) in Pan-STARRS1, the object has the colorimetry more typical of a galaxy in those images.

st 3 dss2 aladinliteSt 4 is the small, round and diffuse object located at the center of this coloured DSS2 image extract. Its morphology is typical of compact Planetary Nebulae. Image credit: DSS2 Aladin Lite.

St 3 ps1St 3 as seen in a Pan-STARRS1 image extract. These images seem to reveal St 3 to have a round morphology with a central condensation. However, Pan-STARRS1 data is also in favour of this being a small unresolved spiral galaxy too. Image credit: Pan-STARRS1 Science Consortium.


St 9 – Possible elongated Planetary Nebula

This is another PN candidate discovered by Xavier Strottner in images from the Digitalized Sky Survey (DSS). Unlike St 3, St 9 is a rather obvious and diffuse nebula (as can be seen in the image below). It appears best in bluer images, such as in the DSS blue plates. The object is also obvious in the Mid-Infrared, displaying a typical Mid-IR signature of a PN!

st 9St 9 as seen in a coloured image from the Digitalized Sky Survey (DSS). Image credit: DSS2 Aladin lite.


Mo 7 – Possible obscured compact Planetary Nebula

Sankalp Mohan (India) discovered this small Planetary Nebula candidate in WISE satellite data, where it diplayed the typical Mid-Infrared signature of a Planetary Nebula. It was initially rejected from being kept as a PN candidate, as it did not display any signs of nebulosity (more observations were needed). It wasn’t until the release of DECaPS in 2018 that Mo 7 was a confirmed to be a nebulous, and hence a Planetary Nebula candidate!

Mo7decapsDECaPS coloured image extract showing Mo 7 as a small round nebula. These were the images that confirmed the objects nebulous nature. Image credit: DECaPS Aladin Lite.

Mo 7 allwiseAllWISE Image extract showing Mo 7 (centered). The “red” colour is due to the colour coding, with the red band corresponding to the WISE W4 filter. PNe usually respond best in these images, hence the colour! Image credit: AllWISE Aladin Lite.


LDû 36 – Possible Round and faint Planetary Nebula

This nice Planetary Nebula candidate was discovered by Pascal Le Dû (France) in images from the SHS Halpha survey. In the visible wavelength, the nebula only seems to appear in these images, even in DECaPS and Pan-STARRS1! The nebula however emits significantly in the Mid-IR, with a signature in WISE images typical similar to many PNe. Its nebulosity also seems to be visible in Mid-IR images.

LDu 36SHS Halpha Image extract showing LDû 36. Notice its round morphology, similar to many Planetary Nebulae. This is the only current optical image available for this object, so far! Image credit: SuperCosmos Halpha Sky Survey. 

LDu 36 spitzerSpitzer image extract showing a faint nebulosity and poorly defined, likely corresponding to LDû 36. Its colour-coded green colorimetry in these images is very common in the case of Planetary Nebulae. Image credit: Spitzer Aladin Lite.

Pre 43 – Possible blue Planetary Nebula with a complex morphology

I first noticed this possible Planetary Nebula in images from the WISE and DECaPS surveys online, where it appears as a rather heterogeneous, clumpy and elongated blue nebula. In images from the Digitalized Sky Survey (DSS) the nebula mixes rather well with the surrounding nebulosity, but DECaPS, Narrow-band (OIII and Halpha) and WISE Mid-Infrared images clearly indicate it to be seperate and an independent nebula!

Pre 43 BertPre 43 as seen in a OIII+NII image extact taken by Bert Van Donkelaar. The nebula appears as a tiny blue patch of nebulosity at the center of this image. The image indicates that Pre 43 emits strongly in the OIII band, typical of PNe. (c) Bert Van Donkelaar.

Pre 43 decapsDECaPS Image extract showing Pre 43. In these images it appears as a complex, heterogeneous, clumpy and elongated blue nebula. The brightest part of this nebula is 0.5′ x 0.7′ in size. This is surrounded by a faint, vague and blue halo measuring perhaps 2′ x 1′ in size. Image credit: DECaPS Aladin Lite.

shs Pre 43 short red halphaImage comparison between a SHS Short Red and Halpha frame showing Pre 43. Notice how the nebula only seems to appear in Halpha. This is typical of Planetary Nebulae as they most often have hydrogen emissions. Image credit: SuperCosmos Halpha Sky Survey.


DeGaPe 51 – Possible vast circular Planetary Nebula

This is an apparently round nebula that appears best in OIII narrow band images, discovered by the APO team (Thierry Demange, Richard Galli and Thomas Petit) in combined narrow band images. The team photographs the sky regularly using OIII, Halpha and SII filters (then combining them them to create a coloured “SHO” image), to obtain images like the one below! Except for in OIII, DeGaPe 51 is optically very faint, being undetectable in most optical surveys, including Pan-STARRS1!

Discovery SHO image extract showing DeGaPe 51. Notice its rather round morhpology as seen in these images, appearing mainly in the OIII band (colour coded blue). (c) APO Team.

DeGaPe 51 SHS HalphaSHS Halpha Image extract of DeGaPe 51. Notice how the object is poorly detectable in this image. Other than these survey images, the nebula seems to be absent in other optical survey, such as the Digitalized Sky Survey and even Pan-STARRS1! Image credit: SuperCosmos Halpha Sky Survey

DeGaPe 54 – Possible Stellar Planetary Nebula

This is yet another Planetary Nebula candidate discovered by the APO team in their combined SHO narrow-band images. This object is very stellar as seen in survey data, not even DECaPS indicate any signs of a nebulous nature! Furthermore, the object displays an Infrared excess atypical of most PNe! Only narrow band images seem to indicate this object to have PN-like charactersistics.

Discovery SHO image extract showing DeGaPe 54, located at the center of this image. Despite its stellar morphology, its flashy green colour in this image clearly distinguishes it from the rest of the background stars! (c) APO Team

DeGaPe 54 DECAPSDeGaPe 54 as seen in the combined colour DECaPS images. Unlike the SHO image, the object is impossible to distinguish from the surrounding stars! This image also suggests the object could be slightly obscured by the nebulosity in this region. Image credit: DECaPS Aladin Lite.


DeGaPe Object 3 – Possible diffuse Planetary Nebula?

As of April 12th, 2018 this is the most recent discovery made by the APO team. It’s a rather faint and diffuse object that could be a Planetary Nebula. However, based on its designation, this status is still pending. The nebula is optically faint (not even detectable in DECaPS images!), essentially emitting in OIII. In the Mid-IR however the nebula is obvious, with a typical PN-like signature in WISE!

Discovery SHO image extract of DeGaPe Object 3. Notice its rather diffuse morhpology as seen in these images, appearing mainly in the OIII band (colour coded blue). (c) APO Team.

Ra 66 – Strongly obscured compact Planetary Nebula candidate

This Planetary Nebula candidate was discovered by Thierry Raffaeili (France) using the available SDSS images online, via The nebula is round and apparently compact. It is optically faint, but it has a much brighter Infrared counterpart (with a Mid-Infrared signal typical of most Planetary Nebulae). Its faintness in optical images is most likely due to this object being strongly obscured behind thick dust of a star forming region.

PN Ra 66 sdssCombined colour SDSS image extract showing Ra 66 as a faint round nebulosity, laying next to a relatively bright star. The colorimetry of the nebula in these images is not typical of a Planetary Nebula, but this effect might just be due to this object being strongly obscured behind thick dust of a star forming region. Image credit: SDSS Aladin Lite.

Ra 66 allwiseCombined Mid-Infrared AllWISE image extract showing Ra 66. Its colorimetry in these images is the typical signature of a Planetary nebula (similar to Mo 7, further above). Image credit: AllWISE Aladin Lite

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 object 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 c2Figure 1: SOHO/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 amateur astronomers, including Michal Kusiak (Poland) and Rob Matson (USA) quickly intervened that same day and confirmed his sightings.

With the available SWAN images at the time of discovery, Michal derived a possible preliminary orbit in favour 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_xilhpEFigure 2: Animation of Comet 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 their resolution. In addition, one can see the comet disappear 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 the object’s peak brightness, as comets tend to be very unpredictable. Indeed, while some comets quickly flare-up into “great comets”, others may brighten slowly or even disintegrate. In fact, both these scenarios are especially applicable to sungrazers! Comet C/2012 S1 (ISON) was a good example of a sungrazer that failed to meet the expectations of many. The comet gained lots of attention from the media over the course of 2012-2013, as it was believed that it could reach a similar peak brightness to the full moon. Unfortunately, comet ISON brightened much slower than many had hoped, reaching no more than mag -2 at its best, before fully disintegrating (see figure 3). Moreover, the ESA/HST failed to recover ISON after perihelion!

comet ison hi1a 20131201Figure 3: Enhanced STEREO/SECCHI HI1-A image extract showing the dusty remnant of comet ISON taken three days after its perihelion. Image credit: NASA/NARL STEREO/SECCHI HI1-A.

Unfortunately, no definitive ground-based observations of comet SWAN were obtained of during its inbound journey, as the comet had already entered daylight as seen from Earth. 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. Consequently, we could only rely on SOHO/LASCO and STEREO/SECCHI to follow up on this object. With only a handful of 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 difficulty in predicting the brightness of comets, most assumed that the object would (at least) be a fainter rival to comet Lovejoy. This implied that it would be clearly visible in the real time (low quality) STEREO/SECCHI HI1-B beacon data. Strangely, however, it was hardly detectable in those images (see figure 4). In fact, the HI1-B images showed the brightness to be typical of a bright (but “ordinary”) SOHO/STEREO comet! This was immediately supported by SOHO/LASCO C3 a couple of days later (see figure 6). Notice the similar appearance between SOHO-3184 (a typical “bright” Kreutz sungrazer) and comet SWAN (see figure 5).  This suggested that the comet it was unlikely going to survive past perihelion.

images/SWAN/SWAN_hi1b_SW.jpgFigure 4: Comet 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 order to explain these unexpected observations, two main hypothesis were initially proposed. The first was that Comet SWAN was originally a much larger object that fragmented while present in the SOHO/SWAN FOV. This meant that the object observed in SOHO and STEREO could be one fragment of an incoming “cluster” of comets. This was rapidly ruled out as no such cluster was subsequently observed. The second explanation was that the object might have had unusually strong Hα-emissions, knowing that SOHO/SWAN (compared to SOHO/LASCO and STEREO/SECCHI) observes the sky in the Hα band. This was equally ruled out after studying the comet using various SOHO filters.

comparison comet swanFigure 5: Comparison 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_5gznpAFigure 6: Animation 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 disintegration). Image credit: ESA/NASA/NRL SOHO/LASCO C3.

On March 14th, the comet entered the SOHO/LASCO C2 FOV (see figure 1). As sadly predicted, it did not re-emerged from perihelion. In fact, the comet had already started fading (disintegrating) while present in the C3 FOV (figure 6). Similarly, the comet’s last moments were recorded by the STEREO/SECCHI COR1 and COR2 cameras. There too it was obvious that comet SWAN was much smaller than comet Lovejoy (see figure 7 and 8).

comet swan lovejoy cor2bFigure 7: Comparison between comet SWAN (left) and comet Lovejoy (right). Notice the very large difference in brightness between the two, comet SWAN being a lot fainter! Image credit: NASA/NRL STERE/SECCHI HI1-B.

output_CjqrInFigure 8: Animation 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.

A couple of days after the comet had vanished, high resolution HI1-B images were made available, showing the comet to briefly display a “forked” tail as a result of the interacting solar wind (see figure 9).

output_NSy9zVFigure 9: Animation 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.

The reason for the comet’s unexpectedly faint appearance remains unknown. Some still speculate that the object suffered an outburst while it was present in the SOHO/SWAN FOV, or that it was a larger comet progressively disintegrated soon after discovery. The answer will most likely never be known.

Although, despite its faintness, it was still a relatively bright SOHO comet. Indeed, it is not every day that the SOHO and STEREO telescopes are treated to a comet of this brightness!

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!