Griffith Observatory Astronomical Observer
Anthony Cook's comet ISON blog


December 4, 2013
by guest blogger Dr. Laura Danly, Griffith Observatory's Curator

Comet ISON is officially defunct, as far as the casual observer is concerned.  No one on Earth has yet reported being able to observe the comet from the ground, so it is too faint to be seen above the morning twilight this week.  Observatories around the world will be searching for comet ISON's remains, in the hope of piecing together what happened to ISON in its final hours. For a full post mortem on the "comet of the century" that wasn't, come to All Space Considered at Griffith Observatory, at 7:30 p.m. on Friday, December 6, in the Leonard Nimoy Event Horizon theater.

November 30, 2013 (2:00 pm  PST)

Fading  comet ISON, now retreating from the sun, is visible at the edge of the SOHO LASCO C-3 coronagraph. The comet will exit the coronagraph’s field of view later today. The Max Plank Institute for Solar System Research (in Germany) has issued an analysis (currently only in German, but translatable with Google) of the expanding dust tail visible in SOHO images. It concludes that dust production of the comet stopped 2 hours after the perihelion (closest approach to the sun) on Thursday. The comet has been inactive since then. It is unclear if the nucleus of comet ISON has fragmented, or if it survived at all. I think the lesson of comet ISON so far has been that only further observation can tell if there is more to ISON’s future or not. I also think, however, that there is no reason to expect that comet ISON will put on any kind of visual spectacle later this month.

November 29, 2013, 12:00 noon PST
by guest blogger Dr. Laura Danly, Griffith Observatory's Curator

Click here to see a movie of comet ISON passing the sun taken by SOHO.  We're all waiting to see how things develop.


November 28, 2013, 9:00 pm PST
by guest blogger Dr. Laura Danly, Griffith Observatory's Curator

After all the dire news today about comet ISON's demise it appears it may be rising from the ashes.  There are some pretty great images being posted from SOHO's LASCO C3 camera.  Check it out!  You'll need to wait a minute -- or maybe several minutes -- for the images to load. The most recent ones are at the top.  At the time of this post, the most recent image had the time stamp 2013/11/29 00:18.  The time is given in Universal Time, which is the same time zone as London. (In the old days it used to be called Greenwich Mean Time.) By the way, LASCO stands for Large Angle and Spectrometric Coronagraph and the C3 coronagraph has the widest field of view. C2 and C1 are nested inside the C3 field of view.  A coronagraph has a mask that blocks out the bright light of the sun so you can see the fainter corona -- or in this case, comet -- around it.  Enjoy!

November 28, 2013

Comet ISON looked promising late last night and early this morning in the SOHO spacecraft’s C-3 coronagraph. Checking back in at about 9 a.m., PST was a bit disappointing. Comet ISON sported a beautiful, long, forked tail, but the intensely bright area surrounding ISON’s nucleus had drastically faded. NASA provided live coverage from the Goddard Spaceflight Center in Greenbelt Maryland where the sensitive instruments of NASA’s Solar Dynamic Observatory (SDO) are controlled, and conducted a live conference with astronomers involved with the observations and with Kitt Peak National Observatory where attempts were made to image the comet during the day. Basically, aside from the lingering tail (which gets stalled by the solar wind and radiation effects), no detection of cometary activity was seen. Two hours after perihelion, the experts concluded “there’s nothing there,” and were nearly certain that ISON did not survive its brush with the sun. Six minutes after the Hang Out ended, the SOHO C2 coronagraph, which provides a view of space closer to the sun than the C-3 coronagraph, a ghostly image of ISON reappearing on the other side of the sun. A cloud of debris? A swarm of active nucleus fragment? Is ISON dead or alive? Stay tuned! Happy Thanksgiving!

November 27, 2013, 3:45 pm
by guest blogger Dr. David Reitzel, Griffith Observatory's Astronomical Lecturer

Comet ISON gave everyone a scare yesterday when radio telescopes measured a dramatic decrease in the production of molecular gas and optical observations were picking up an increase in dust production. These together led many to speculate that the ISON had finally disintegrated. As the day went on, however, ISON continued to brighten! Was this an expanding dust cloud, or is the nucleus of ISON still intact?

As of today, ISON has brightened dramatically in the SOHO wide-angle C3 coronagraph. It seems that despite the odd behavior, ISON is still with us. In fact, ISON is now so bright that the detector is "blooming" in a bright horizontal streak. Experts have expressed that this blooming begins at magnitude +0.5, or about as bright as the planet Mercury in the sky. ISON is now much brighter than that and increasing brightness very fast. At the time of this post, estimates of a visual magnitude of -1 to -2 were appearing. That makes ISON brighter than the brightest stars in the sky and it is now behaving like other sungrazing comets. Will it survive? That remains to be seen, but right now, it is still looking good.

Even though ISON is brightening by many tens of times, do not attempt to observe the comet during the day. It is still too faint to see with your naked eye and any telescopic or binocular viewing is exceptionally dangerous and should not be attempted. If any magnified sunlight enters your eyes, it will cause permanent damage to your eyes, and could lead to blindness. Instead, keep an eye on the space observatory pages linked above to see if Comet ISON manages to hold itself together against the intense sunlight or if it succumbs to the sun. We could be in for a spectacular Thanksgiving day show.

Watch Comet ISON’s close-approach to the Sun from Space

NASA has several spacecraft that continuously monitor activity on the sun and the solar corona. Because comet ISON is passing very close to the sun on November 28, several of these space solar observatories are ideally positioned to show us comet ISON at its brightest, when it is closest to the Sun. These include “STEREO Ahead”, one of two spacecraft that are close to earth’s orbit, but that are positioned on the far side of the sun from our point of view. SOHO and STEREO monitor the sun from relatively close to the Earth.

November 21-28. Comet ISON slowly crosses the view of NASA’s STEREO Ahead Spacecraft’s H1 coronagraph. The Ahead spacecraft is as far from the sun as the earth, but almost on the other side of the sun from us. These images are low-resolution and are intended to provide a “quick look” at the comet’s progress. NASA will release the full resolution images view days later, after processing. A special NASA Webpage provides an explanation of what can be seen in the images.

November 26-30 Comet ISON appears in the SOHO wide-angle C3 coronagraph, and will allow viewing the comet to within 2 degrees of the sun. Movies showing the latest 48 hours of images can be seen here.

November 28. Comet ISON is in the view of SOHO’s narrow-angle C2 coronagraph between 4am and 2pm on November 28. The device that blocks the sun from SOHO’s camera will also block the view of some of the comet between about 9:00 a.m. and 2:00 p.m. Movies showing the latest 48 hours of images can be seen here.

From approximately 9:09 a.m. to 12:19 p.m., PST, the Solar Dynamics Observatory will attempt to image comet ISON in ultraviolet wavelengths. Images will appear on their special Comet ISON Perihelion Page shortly before 10:00 a.m., PST.

November 26, 2013

Comet ISON continues to lend itself to conflicting interpretations of its behavior, now less than 2 days from its scorching encounter with the sun. While clouds interfered with observing at Griffith Observatory last week, images of the steadily brightening comet came in from around the world. Some examples are from November 22 and November 23. The clear weather on the morning of November 24 allowed me to attempt observing again from Griffith Observatory. I could see planets Mercury and Saturn and stars of Libra against the light of dawn. But neither binoculars, my 70mm refractor, nor the 12-inch Zeiss refractor revealed the comet between 5:35 a.m. and 6:00 a.m., PST. I was puzzled. Observations posted by observers around the world soon solved the mystery. Because comet ISON moved into the field of view of NASA’s STEREO Ahead H-1 coronagraph, astronomers are able to get a continuous and consistent set of brightness measurements. Kitt Peak astronomer Matthew Knight reported on the Yahoo Comet mailing list that “These show that the comet was mag 5.3 when it first appeared in (STEREO’s) HI1A on Nov 20, peaked around 4.3 on Nov 22, and gradually faded on Nov 23, reaching about 4.6 on Nov 23.96 (UT).” So when I observed from Griffith Observatory, the comet had already faded. (A Los Angeles observer named Vince Victor did succeed in imaging the comet from the San Gabriel mountains on the 24th) Since then, the comet has started to brighten again, and is now magnitude 3.7. However, no visual observation of the comet has been reported since the 24th.

Based on the dimming on the 23rd and low molecular emissions detected by microwave instruments as reported in Sky and Telescope Magazine's November 25 update, some astronomers speculated that comet ISON had died, with only the slowly spreading dust and gas from its depleted nucleus keeping it visible. The resumption of the comet’s brightening and the fairly vigorous appearance in the most recent STEREO images, however, contradicts these dire assessments. Comet ISON is at least temporarily out of our direct view in the glare of the sun, but you can see for yourself what it is doing on the space solar observatory links at the head of this blog. I am looking forward to the view from NASA’s SOHO satellite, from which the comet will start to be observable later tonight.

November 21, 2013

While our view of comet ISON at dawn continues to be obscured by clouds and rain across southern California, observations made from other parts of the world show that comet ISON continues to brighten. According to Bruce Gary in Arizona, the comet was magnitude 3.7 this morning, easily visible to the unaided eye in good conditions. From clear skies, the comet is very photogenic, as seen in these gorgeous views from Africa and from the Canary Islands.

November 19, 2013

Comet ISON continues to brighten. Reports from around the world indicate that it has reached magnitude 4.8, potentially visible to the unaided eye from dark skies. The comet’s tail is more than 7 degrees long, an actual length of more than 9 million miles. The tail now shows turbulent interaction with the solar wind. The Max Planck Institute for Solar System Research in Germany has concluded that ray-like structures in the coma (the bright head of the comet) are from fragmentation of the comet’s icy nucleus. I did manage to see the comet on the morning of the 18th. While its brightness was similar to what I saw on the 14th, the comet was very hard to see against the light of the nearly full moon even with a telescope, and no hint of the tail was visible.

November 14, 2013

I went to bed after having read a Twitter post announcing that observers in Europe had just seen ISON by unaided eye and that the comet was undergoing a surge in brightness. I woke up at 5:00 a.m. and saw the comet through my 70mm refractor. The comet was easy to find, its coma appearing as a bright, jade-colored disk with a bright starlike center. It still appears the same size as last night. I estimate its brightness as magnitude 5.8, 6 times brighter than what other observers reported 24 hours ago! The tail was still too faint to see against suburban light pollution. Only time will tell if the change in appearance is a temporary outburst, or will continue until the comet becomes spectacular!

November 13, 2013

I saw comet ISON from my back yard this morning using a 70mm refractor at 20 power. It appeared as a ghostly round glow, twice the apparent size of Jupiter. I could not see the tail against the suburban sky glow in Pasadena, California. Using a 5.5-inch f/3.5 Schmidt-Newtonian, I was able to photograph the comet (with a half-degree long tail). Processing to make the tail visible against the light-polluted sky results in the grainy appearance:


Comet ISON on November 13 at 5:00 a.m. PST. 12 15 - second exposures at ISO 400 were combined to create this view.

November 12, 2013

Speeding sunward at 120,000 miles per hour (50 km/s), comet ISON is now inside the orbit of Venus. Today, Michael Jaeger obtained another stunning image of the comet from Europe before dawn. It shows a broad dust tail and a slender ion tail. Amateur astronomer Bruce Gary, who has been performing excellent photometric (brightness measurement) observations of Comet ISON almost daily since he made the first recovery of the comet from behind the sun in August, reports that ISON is now brightening at a steady rate of 15 percent per day and has been since October 28. On November 8, ISON was shining at magnitude 7.9. Consistent with that measurement, other observers have reported seeing ISON through ordinary 7x50 binoculars from dark (light-pollution free) sites. Comet ISON appears to be on track to reach magnitude 6 (possibly visible by the unaided eye) by November 20. NASA has made a downloadable paper model of comet ISON’s trajectory near the Earth and the Sun.

November 6, 2013

JPL comet expert Zdenek Sekiana has released the newest weekly update on the “close to anemic” behavior of comet ISON up to November 2. (http://arxiv.org/abs/1310.1980). He concludes that “prospects of a spectacular show near perihelion appear to be now less likely than ever before." Since that was written, however, observers have reported some interesting changes in the comet. Photographs are beginning to show some structure in ISON’s tail, and after being stable for more than a month, over the last week the amount of gas emitted by the comet has doubled, mostly in the last 3 days. Visually, the comet is reported to have suddenly developed a strongly condensed core, and is as bright as magnitude 8.0, with at tail 0.6 degree long and visible in dark skies through 10X50 binoculars. Is ISON just waking up?

October 31, 2013


I opened the Griffith Observatory 12-inch refractor at 4:30 in the morning to observe comet ISON. I could not see the comet at the expected position, so after an hour had to take a break to print a detailed star chart. At 6:03 a.m., PDT, after dawn had started, I could see the faint image of the comet in my camera, but was unable to see it through the eyepiece. 10 exposures of 30 seconds each, taken between 6:09 and 6:21 a.m. were combined to make this 5-minute exposure of the comet. The graininess resulted from subtracting some of the light pollution and dawn glow from the picture in order to make the comet more visible. It was exciting to at last make contact with ISON, albeit indirectly!


Here is the comet and the moon at the same scale with the 12-inch on the morning of October 31.


October 30, 2013

Comet ISON is very diffuse, glowing at between magnitude 8 to 10 depending on the observer, and is healthy but developing slowly–or is on the verge of disintegrating as soon as this week–depending on which comet expert is consulted. A growing number of astronomers are coming to the conclusion that comet ISON is unlikely to ever become visible to the unaided eye unless it releases a large amount of material after its nucleus passes close to the sun on Thanksgiving Day. The comet continues to show a slowly lengthening yellow tail and a green coma in recent photographs. Comet ISON moves from Leo the Lion to Virgo the Maiden on the 5th. The comet is about 30 degrees high in the east-southeast at dawn (5:50 a.m., PDT or 4:50 a.m., PST) and can be seen in a 4-inch or larger telescope from dark skies.


October 23, 2013

Comet ISON, now in Leo the Lion, continues to slowly brighten as it approaches its November 28 close encounter with the sun. Although moonlight is currently a problem, the comet is visible through 5- inch telescopes. Astrophotographers equipped with telephoto lenses and sky tracking mounts will want to shoot ISON before dawn on the 25th as it poses with the galaxies M95, M96 and M106 in Leo.


October 16, 2013

Another eye-catching sight at the start of dawn is the close pairing of planet Mars and Leo the Lion’s bright star Regulus. They are about half as high as Jupiter, but in the east. Mars and Regulus look about equally bright but contrast strongly in color–Mars has a deep rust hue while Regulus has a blue tint. Comet Ison also is within 2 degrees of Mars, but bright moonlight will make the faint comet very difficult to see this week.


October 9, 2013

Comet ISON, about 160 million miles from earth, closes from 1½ degrees to 1 degree north of Mars this week. On the 14th, Regulus, Mars, and comet ISON align: Mars is 1 degree north of Regulus, and the comet is 1.1 degree north of Mars. Although comet ISON remains a faint telescopic object, it is a colorful and attractive object in telescopic photographs.


September 25, 2013

The orange planet Mars, appearing as faint as it ever does at magnitude 1.6, is in Leo the Lion. It rises in the east at 3:00 a.m. and is 28 degrees above the eastern horizon at 5:24 a.m. at the start of dawn. Comet ISON passes only 6.7 million miles from Mars on Tuesday, October 1. At the same time, both Mars and the comet are 199 million miles from earth. NASA’s Curiosity rover and the Mars Reconnaissance Orbiter will try to study the comet during its passage by Mars. In our sky, comet ISON, now at about magnitude 10 (10,000 times fainter than Mars), can be found through a telescope, just under 2 degrees north of the planet.


September 4, 2013

Comet ISON, C/2012 S1, also is in the vicinity of Mars and the Beehive Cluster, but remains a feeble magnitude 14, about a thousand times too faint to see by the unaided eye. Astronomers are carefully monitoring the comet to see if it will burst into activity as it draws closer to the sun, but for now at least, comet ISON is continuing the same halted development that it has been displaying since January.


August 28, 2013

Comet ISON (C/2012 S1), which was promoted widely last year as the upcoming “comet of the Century,” is in Cancer the Crab, to the lower left of Mars at dawn. The comet glows feebly at magnitude 14, one thousand times fainter than the faintest star visible to the unaided eye, and several times fainter than most predictions had anticipated. As a result, the comet remains visible only to experienced amateur and professional observers at this time. As observing prospects become clearer before the comet ISON’s close encounter with the sun on Thanksgiving Day, Griffith Observatory will provide detailed observing information, assuming the comet eventually brightens enough to observe easily.