Saturday, November 30, 2013
Venus over Chinatown
Comet C/2012 S1 ISON Keeps On Keeping On (29 November UT)
|Comet C/2012 S1 ISON seen in the SOHO LASCO C3 instrument from 12:30 UT 29 November.It is 0.107AU from the Sun by the end.||C/2011 W3 Lovejoy in SOHO C3 (16 December 2011 UT). Lovejoy is 0.08 AU from the Sun here. Image credit NASA/SOHO|
Comet ISON keeps on going, despite several news reports suggesting its demise, the comet still looks more or less comet like over 24 hours from perihelion (for views of what it looked like then see here, and its subsequent return here and here). For comparison I show the other great survivor, comet C/2011 W3 Lovejoy.
Lovejoy was brighter, and continued to brighten developing a spectacular tail before its ultimate demise. ISON is fading slowly, although what is probably the synchronic tail is developing nicely.
It is still too early to write ISON off yet, but it is also still too early to determine if we can see it in the skies in the next few days.
A nice ABC article immediately post perihelion, which quotes me, is here.
Friday, November 29, 2013
Comet C/2012 S1 ISON stays on track (29 November UT)
|Comet C/2012 S1 ISON seen in the SOHO LASCO C3 instrument at 06:18 UT 29 November. Stars indicated for comparison with chart. Click to embiggen||Chart of the predicted position of ISON at 06:18 UT 29 November.Click to embiggen|
In the wake of the dramatic breakup and revival of comet ISON as it rounded the Sun, once again there has been speculation that it is significantly off track.
Here I show one of the latest SOHO images together with the predicted position of ISON at the same time, using old orbit parameters. ISON is exactly where it should be, between Chi Ophiuchus and the dim star TYC-6210-254-1. Measuring their positions I find the present position of ISON is within 6" of teh predicted poition, well within the measurement error from the images.
Pre-perihelion track positions diagram and predictions are here.
Note the broad fan shape of comet ISON at the moment, comet ISON seems to be reviving, a bit. But it is still not clear what we are seeing is a pile of gravel with attitude, or a substantial chunk of comet remnant. Karl Battams and the STEREO team think it likely that there is a substantial chunk of material, Terry Lovejoy and Jacub Cerny think it likely there is not.
All I can say is keep on watching, even if it is just gravel with attitude, it is still beautiful and we can still learn a lot.
Comet ISON, It's Not Dead Yet! (it may go for a little walk)
|Latest 12 images from the SOHO LASCO C3instrument animated. Comet ISON breaks up, but some comet-looking material comes out the other side. You can see the remnants of the old tail on the other side of the Sun.||Latest 30 low resolution beacon images from the STEREO COR2B instrument animated. As for LASCO C3 you can see a big bright blob of material coming out.|
C/2012 S1 ISON continues to amaze. After fizzing out, it seems to have turned on again. Whether this is just a bunch of gravel fizzing out or a fragment of nucleus turning on again, as happened with comet Lovejoy is not clear. Because of the orientation of the comet and it's orbit in COR2B it looks like it is spinning, but this is just a line of sight effect. However, looking carefully at the image it may be that we are seeing the beginning of new tail production. Only time will tell, so we need to keep on watching.
Monty Python: "I'm not dead yet!".
Is Comet C/2012 ISON channelling comet Lovejoy? (post perihelion, 28 November 2013)
|Latest 30 images from the SOHO LASCO C2 instrument animated. Comet ISON breaks up, but some material comes out the other side.||Latest 30 low resolution beacon images from the STEREO COR2A instrument animated. The Big blob is Venus. As for LASCO C2 you can see the breakup, but something continues on.|
C/2012 S1 ISON reached perihelion. And then broke up, and then something continues on. It might be just gravel and dust, or there might be a chunk big enough to be comet like. This is not unlike what happened to comet Lovejoy. Only time will tell if there is a chunk big enough to turn on again.
Insert favourite Monty Python or Princess Bride Quote here.
Thursday, November 28, 2013
Comet C/2012 S1 ISON Brightens More, Prospectes for Perihelion (28 November 2013)
|Latest 30 images from the SOHO LASCO C3 instrument animated. Comet ISON skims past delta Scorpii.||Latest 30 low resolution beacon images from the STEREO COR2A instrument animated. The Big blob is Venus.|
We are just over 7 hours away from comet C/2012 S1 ISON reaching perihelion. What an amazing trip it has been, with the comet defying all expectations, stops and starts in brightness increase, dramatic outbursts and fades.
Now on the last leg of its long journey, which began around a million years ago in the Oort cloud at the edge of the solar system, in a few short hours it will skim around a solar diameter from the surface of the sun, being exposed to almost unimaginable heart wich will vaporize the very dust on its surface.
Will it survive is the question on everyone's lips? How bright will it get?
Currently it is outperforming C/2011 W3 Lovejoy, latest brightness estimates put it at around magnitude -3 (a bit dimmer than Venus ), quite a bit above Lovejoy at the same time, and ISON has a more complex tail. The twin tails you see in the LASCO C3 instrument are a broad dust tail and a synchronic dust streamer. No ion tail can be seen in the LASCO C3 image at the moment (info from the latest CBET via Jakub Cerny).
So, what happenes next? Will it disintegrate? For typical Kreutz sungrazer comets with radii under 100 meters, they tend to disintegrate at 10 solar radii from the Sun. ISON is much larger than 100 meteres (somewhere between 1 Km and 2.4 Km in radius), but the 10 Solar radii checkpoint is at around 12:00 UT in a half an hour from now as I type. If it passes this check point, then there is a good chance it will get to perihelion. After that, it's all still up in the air. Karl Battams of the STEREO mission is enthusiastic but cautious. Jakub Cerny has a detailed post here were he expects it not to survive.
How bright will it get? Jakub Cerny reports J. N. Marcus as saying it will not get too much brighter, as the heat from the Sun begins to vaporise the dust grains.
If it survives perihelion, it's grazing approach to the Sun, what happens then? Will it be like Lovejoy and disintegrate a few days later, leaving us with a pale and impressive tail? Perhaps the best analogs will be two sungrazers of around 1 Km radius, the great Southern Comet of 1880 and C/1970 K1, which survived and were reasonably bright with decently long tails for a short time.
So if ISON survies we might expect it to not be as bright as C/2006 P1 McNaught, but brighter than Lovejoy.
The best we can say is "don't count your comets before they are hatched". As the excitement mounts you can watch the comet in various spacecraft instruments (links here) . No matter what happens, this is the first sungrazing comet from the Oort cloud, so the show will be well worth watching.
So happy comet watching folks.
Is Comet C/2012 S1 ISON on Track?
|Comet C/2012 S1 ISON seen in the SOHO LASCO C3 instrument at 05:06 UT 28 November. Stars indicated for comparison with chart.||Chart of the predicted position of ISON at 05:06 UT 28 November|
There has been some rumination on the interwebs that comet ISON is off course. Here I show one of the latest SOHO images with the predicted position of ISON, using an old orbit. ISON is exactly where it should be; right next to delta Scorpii.
Comet C/2012 S1 ISON Brightens, comparison with Lovejoy (28 November 2013)
|Comet C/2012 S1 ISON in the SOHO Lasco C3 imager at 00:30 UT 28 November 2013||Comet C/2011 w3 Lovejoy in the SOHO Lasco C3 imager at 09:30 UT 15 December 2011||Overlay of the two images|
Comet ISON continues to brighten, its head is now brighter than comet Lovejoy at a similar distance from the Sun in the STEREO imager (ISON was at 0.084 AU from the Sun in this image, Lovejoy was closer at 0.079 AU). ISON's tail is a bit wimpier though.
What does this all mean for ISON's chances of survival? Who knows, we just have to keep watching.
How Bright is ISON? Comparing Comet ISON to Lovejoy
How bright is comet C/2012 S1 ISON now? It's pretty hard to tell with the images we have, as we don't really have high resolution images with good comparison stars at the moment. So I've compared ISON as it looks now to C/2011 W3 Lovejoy as it looked when it just entered the SOHO LASCO C3 imager and STEREO COR2B imager.
Both comets look roughly the same in the SOHO images, but Lovejoy looks brighter in the COR2B images. Unfortunately I don't know where Lovejoy was with respect to COr2B, so I don't know if this is due to the comet being closer to the camera.ISON looks around the same brightness as
Still, overall it is looking similar to Lovejoy at the moment, perhaps it will perform like Lovejoy?
Wednesday, November 27, 2013
Comet ISON Reaches Perihelion Tomorrow (28 November 2013)
At this time it is a mere degree (that's one fingerwith) form the Sun (see here for diagrams). If you are not an experienced solar observer DO NOT look for it in daylight, your eyes can be severely damaged by exposure to the Suns glare.
However, a bevy of spacecraft will be observing, and you can watch from the safety of your computer screens.
These times are taken from Karl Battams info sheet.
November 28, 0400UT: Enters STEREO/SECCHI COR-2A (15:00 AEDST)
November 28, 1300UT: Enters SOHO/LASCO C2 (24:00 AEDST)
November 28, use links above for everything except the SDO.
~1600 - 2300UT: Transits STEREO/SECCHI COR-1B (10:00 29th AEDST)
~1700 - 2200UT: Transits STEREO/SECCHI COR-1A (15:00 AEDST)
~1720 - 1920UT: Transits SOHO/SUMER (15:00 AEDST)
~1810 – 2010UT: Transits STEREO/SECCHI EUVI-B (15:00 AEDST)
~1820UT +/- ?? hr: Transits SDO/AIA! (15:00 AEDST)
Post-Perihelion: November 28 2300UT: Exits SOHO/LASCO C2 (10:00 29th AEDST)
November 29 1400UT: Exits STEREO/SECCHI COR-2A (01:00 30th AEDST)
November 29 2000UT: Exits STEREO/SECCHI COR-2B (07:00 30th AEDST)
November 30 2300UT: Exits SOHO/LASCO C3 (10:00 31st AEDST)
November 31 0000UT: Enters STEREO/SECCHI HI-1A (to Dec 7) (11:00 AEDST)
There is always some lag in transmission from the spacecraft to Earth, so you won't actually be watching live, but it will be pretty close.
Comet C/2012 S1 ISON meets a Coronal Mass Ejection (or does It?) 27 November 2013
|Comet C/2012 S1 ISON in the field of view of the STEREO COR2B imager (lower left). Jupiter is the bright dot center left. Animation of 30 STEREO images. Click to embiggen.||Comet C/2012 S1 ISON in the field of view of the SOHOLASCO C3 imager (lower left). Animation of 30 SOHO images. Click to embiggen.|
Comet ISON may not have reached unaided eye visibility, but it is certainly putting on a show in the bevy of spacecraft observing it. Today ISON entered the field of view of the STEREO COR2B imager and the SOHO LASCO C3 imager. We only have the low resolution images from the STEREO COR2B imager at the moment, but it appears to have caught a dramatic moment.
When a Coronal Mass Ejection blasts out of the Sun and slams into the comet, causing great disruption to the tail.
As you can see, at the time the time (around 4:40 UT) when the CME apparently slams into the comet in COR2B, it is nowhere near the comet in LASCO C3.
If you look at the image to the left, this is the NASA Goddard solar wind/CME model, you may need to click on it and embiggen to see in detail, but the CME blasts out bottom right and misses ISON (top right) by a great distance.
The apparent CME impact is just a line of sight effect.
As ISON makes its final plumet into the Sun tomorrow, it may encounter, or appear to encounter, other CME's. Interpreting these will require a good understanding of where the CME actually is, and avoid confounding by line of sight effects.
Tuesday, November 26, 2013
Comet C/2012 S1 ISON in STEREO H1A (23 November 2013)
|Comet C/2012 S1 ISON imaged in the STEREO satellites H1A instrument on 23 November. 2P/Enke is to the top right and ISON is the big bright thing to the centre. 13 images stacked in ImageJ and aligned then the images differenced to cancel out stars. The vertical lines are imaging artefacts from Earth being too bright (off screen).Click to embiggen||Comet C/2012 S1 ISON imaged in the STEREO satellites H1A instrument on 21 November. 2P/Enke is to the top right and ISON is the big bright thing to the bottom left. 26 Images stacked in ImageJ, then the images differenced to cancel out stars and assembled into an animation. The vertical lines are imaging artefacts from Earth being too bright (off screen).Click to embiggenYou will need to click on the image to embiggen it.|
Comparison of Comet ISON on the 21st and 23rd in high resolution stereo H1A fits images. While there is a lot of debate over ISON's fate, I think these images show the comet is still in play.
In the images above I have used Comet Al's ImageJ macro for using image differencing to really pull out the detail in the comet.
Although to the same scale comet ISON looks a trace dimmer on the 23rd vs the 21st, however this is basically image brightness scaling issues. You can see the comet apparently change significantly in brightness, but comet 2P Enke does the same in parallel. ISON has an extensive tail with what looks like knots of material moving down it, just as in the 21st.
In the images below I have taken a different approach, using a log transform to try and bring out some of the detail in the comets tail. It gives a somewhat different view of the knots moving down the tail, and extensive billows of material in the tail.
I have not had a chance to do calibrated estimates of the comets. However, I think the imminent demise of ISON is less likely from these images and the medium resolution images from the 25th.
|Comet C/2012 S1 ISON imaged in the STEREO satellites H1A instrument on 23 November. 2P/Enke is to the right and ISON is the big bright thing in the centre. 13 images stacked in ImageJ and aligned then LOG processed to enhance dim details. Click to embiggen. Asteroid Kleopatra is towards the bottom of the image.||Comet C/2012 S1 ISON imaged in the STEREO satellites H1A instrument on 21 November. All 26 Images stacked in ImageJ, then the images LOGed to enhance detail and assembled into an animation. You will need to click on the image to embiggen it.|
The Sky This Week - Thursday November 28 to Thursday December 5
The New Moon is Tuesday December 3. The Moon is at perigee on the 4th.
Evening sky looking west as seen from Adelaide at 21:00 pm ACDST on Thursday December 5. Venus is quite high in the evening sky above the Teapot asterism of Sagittarius. The inset shows the telescopic view of Venus. Similar views will be seen elsewhere at the equivalent local times. Click to embiggen.
Venus slowly falls back in the evening twilight. It can easily be seen shortly after sunset (indeed, with a little effort you can see it before sunset) until late in the evening.
The brightest (spectacularly so) object above the western horizon it is still visible up to three hours or more after sunset (depending on how flat your western horizon is) when the sky is fully dark. Venus is beginning to sink to the horizon, but will be spectacular for many weeks hence.
Venus is in the Constellation of Sagittarius. It is a distinct crescent moon shape in even small telescopes. This week Venus is above the "Teapot" asterism of Sagittarius and is not far from the crescent Moon on December 3rd.
Jupiter is in the constellation Gemini. Mars is is in the constellation of Leo but moves into Virgo by the end of the week. Saturn and Mercury are in Libra.
Mars rises still higher in the morning twilight, and is visible well before twilight. The crescent Moon is close to Mars on the 28th.
Jupiter is now well above the northern horizon near the bright stars Castor and Pollux, the twins of Gemini. It is quite easy to see in the morning sky well into the twilight. Jupiter's Moons are now readily visible in binoculars. There are some good Moon events on the 1st and 2nd. Jupiter rises around 10:30 pm local daylight saving time, but is best for telescopes in the early morning.
Mercury and Saturn are just visible low in the eastern horizon before dawn. They are visited by the Moon on December 2, but will be very difficult to see unless you have a flat, level horizon..
Comet C/2013 R1 Lovejoy and Comet C/2012 S1 ISON are no longer visible. If ISON has survived its journey around the Sun on the 28th then it may be spectacular in the morning skies of the Northern Hemisphere.
There are lots of interesting things in the sky to view with a telescope. Especially with Venus so prominent in the sky. If you don't have a telescope, now is a good time to visit one of your local astronomical societies open nights or the local planetariums.
Printable PDF maps of the Eastern sky at 10 pm AEDST, Western sky at 10 pm AEDST. For further details and more information on what's up in the sky, see Southern Skywatch.
Labels: weekly sky
Has Comet ISON disintedgrated? (or is it disintedgrating)
There has been a lot of buzz in the astronomy community over the last 8 hours of so over news that comet C/2012 S1 ISON may be breaking up/ has already broken up. There are several elements to this.
A CalTech team using the IRAM millimeter telescope in Spain has reported a 20 fold fall in molecular emission lines from 21 November to 25 November. They interpret this as a disintegration of the comet. The TRAPPIST team reports a fall in dust production rates by a factor of 3, AfRho measurements by the CARA team suggest nuclear erosion. Terry Lovejoy has measured strong non-gravitational forces which may suggest a breakup. Dan Fishers notes an alternate view of the CalTech results.
Against this the comet looks healthy and brightening in the STEREO images. This could be due to the comet being an expanding cloud of reflective dust though.
Comet C/2012 S1 ISON, more tail action in H1A (23 November, 2013)
Comet ISON in medium resolution PNG images from STEREO H1A,while more detailed than the beacon images, they are somewhat limited for analysis, using 38Ari, Lambda Ceti, Mu Ceti and Xi Tau (O Tau that I used for the images from the 21st is behind the label), the comet stars of around magnitude 2.7 (this is probably fainter than it actually is due to the CCD response of H1A and pixel saturation in the processed PNG), and the comet brightening by 0.5 magnitudes over the course of the day.
Monday, November 25, 2013
Comet C/2012 S1 ISON in STEREO H1A, great tail action (21 November 2013)
|Comet C/2012 S1 ISON imaged in the STEREO satellites H1A instrument on 21 November. 2P/Enke is to the top right and ISON is the big bright thing to the bottom left. Single frame of 26 images stacked in ImageJ and aligned then the images differenced to cancel out stars. The vertical lines are imaging artefacts from Earth being too bright (off screen).Click to embiggen||All 26 Images stacked in ImageJ, then the images differenced to cancel out stars and assembled into an animation. You will need to click on the image to embiggen it.|
Comet ISON has moved further into the field of view of the STEREO H1 inager, and it looks quite stunning.
In the images above I have used Comet Al's ImageJ macro for using image differencing to really pull out the detail in the comet. Comet ISON shows amazing detail in it's tail, there may be some tail rotation, and you can see knots of material moving down the comets tail. In contrast Enke's tail is quite thin, but whips around a fair bit.
In the images below I have taken a differnt approach, using a log transform to try and bring out some of the detail in the comets tail. It gives a somewhat differnt view of the knots moving down the tail.
It tried estimating the magnitude of the comet using the reference stars Rho Ari (5.56), 38 Ari (5.18), Lambda Ceti (4.69), Mu ceti (4.28) and O Tau (3.61). It get the comet starting at magnitude 5 at the begining of the day, and magnitude 4.5 by the end of the day. This is probably an underestimate due to the spectral response of the H1A CCD camera. My estimate of the magnitude of Enke was 5.5, a full magnitude less than predicted.
However, the key point is irrepective of the absolute magnitude, the comet is steadily brightening. An analysis of the brightening of images from the 23rd.
Certainly, whatever happens in the next few days, ISON is giving us a pretty good show.
|Comet C/2012 S1 ISON imaged in the STEREO satellites H1A instrument on 21 November. 2P/Enke is to the right and ISON is the big bright thing to the bottom left. Single frame of 26 images stacked in ImageJ and aligned then LOG processed to enhance dim details. Click to embiggen||All 26 Images stacked in ImageJ, then the images LOGed to enhance detail and assembled into an animation. You will need to click on the image to embiggen it.|
Readers Images of comets ISON and Lovejoy
Reader Krishan Kara sent me these marvellous shots of comet C/2012 S1 ISON and C/2013 R1 Lovejoy, taken on November 19 in Brisbane (note that he holds the copyright on these images, so please ask if you want to copy or use them). The most amazing thing about these shots is that they are unguided! Great work Krishan..
Sunday, November 24, 2013
Comet C/2012 S1 ISON enters STEREO H1A (20 November, 2013)
|Comet C/2012 S1 ISON imaged in the STEREO satellites H1A instrument on 20 November. 2P/Enke is to the right and ISON is the big bright thing to the bottom left. 13 images stacked in ImageJ and aligned . Click to embiggen||12 Images stacked in ImageJ, then the images differenced to cancel out stars and assembled into an animation. You will need to click on the image to embiggen it, The process crops out ISON, but you can see the movement of Enke's tail.|
Comets ISON has finally entered the field of view of the STEREO H1A instrument. The left-hand image was processed in ImageJ as usual, The right-hand image was processed using a difference macro in ImageJ which subtracts out non moving pixels to bring out more details with the comets. Enke and ISON have active tails (which you can't see for ISOn as it just enters in the last few frames), but you may wish to compare the 20th in H1A with the comets appearance on the 20th in H2A.
4BC radio interview on Antibiotics
Saturday, November 23, 2013
Comet C/2012 S1 ISON, good tail action in STEREO (20 November, 2013)
|Comet C/2012 S1 ISON imaged in the STEREO satellites H2A instrument on 20 November to 14 November. 3 comets, Mercury and the Pleiades are labelled so you know where to look in the animation. 12 images stacked in ImageJ, aligned then the imges differenced to cancel out stars. Click to embiggen||12 Images stacked in ImageJ and assembled into an animation. You will need to click on the image to embiggen it, so that you can see ISON, Lovejoy and 2P/Enke and their tails at their best.|
The latest images of comets ISON, Lovejoy and Enke in the STEREO H2A instrument. The data was processed using a difference macro in ImageJ which subtracts out non moving pixels to bring out more details with the comets. Enke and ISON have active tails, and I may have caught the edge of a tail disconnection event with ISON.
14th, reprocessed using Comet Al's difference macro to the same scale (the Pleiades is near the leftahnd edge and Mercury is just entering the field).
You can clearly see the active tail now, and the brightness jump when the out burst occurs is still readily seen.
ISON is very obviously brighter on the 20th, have to do some astrometry to determine how bright.
I have lots of images to download and process, this may take a while. But clearly the plotting of tail and brigness evolution is well worth it.
Friday, November 22, 2013
Comet C/2012 S1 ISON in STEREO H1 A Beacon Images (20-22 November, 2013)
|Comet C/2012 S1 ISON as seen in the low resolution beacon images from the H1A instrument form 20-22 November. Nice and bright with a good tail. The tow bright objects are Mercury and Earth, respectively.||Animated GIF of the 10 frames of ISON entering the H1A imager. Click to embiggen. Looks like there is some significant tail activity.|
Comet C/2012 S1 ISON continues to pass through the field of view of the STEREO H1A instrument. Even in the low resolution images at the momen it is looking good, much brighter than 2P/Enke was.It should be great when we get the high resolution images in a couple of days.
Comet 2P/Enke in STEREO, 19 November 2013
While waiting of comet ISO to turn up in the high resolution STEREO H1A images (as opposed to the low resolution beacon images) here's a nice image of 2P/Enke in H1A. Comet Al gave me his ImageJ macro for using image differencing to really pull out the detail in the comet. You can see some great motion in the tail of the comet this way, better than the raw images.