Comet 17P/Holmes coma now over 5.5 million km wide: 4 times size of the sun!

Using my photograph of the 29th, astrometrically measured with Astrorecord, I updated my diagram of the growing size of comet 17P/Holmes' coma.

The coma is now over 5.5 million km wide. That is 4 times the size of the sun!

Two comets in one picture

After a week of clouds, the 29th December was a clear day. So in the evening I took the opportunity to bicycle 25 minutes to my dark spot "De Wilck" (Cospar 4354) a few km outside the town, with my new small portable Meade ETX-70 rich-field telescope.

The goal: getting some pictures of comets 17P/Holmes and 8P/Tuttle with my small Canon Ixus compact camera piggyback on the telescope.

I managed to shoot a nice picture showing both comets in one wide-field image, with the galaxies M31 and M33 as a bonus. It is shown below: it is a stack of 8 photographs exposed 15 seconds each.

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I also made a series of images of 17P/Holmes with the Ixus zoomed in at maximum. Unfortunately, after 13 images the battery of the camera was empty. Below is the stack of these 13 photographs, exposed 15 seconds each with the ETX-70 as guiding scope:

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USA 193

A belated report on my December 22 observations. December 22 was a clear, albeit moonlit night. Three objects were captured: Lacrosse 3 (97-064A), Lacrosse 5 rk (05-016B), and the failed reco satellite USA 193 (06-057A), which was the highlight of the evening. In addition, a stray was captured in one of the USA 193 images, which turned out to be the Russian Okean-O rk (99-039B).

USA 193 made a high pass. Bright and very fast due to it's low altitude, it was a spectacular appearance. It was over 20 seconds early relative to Mike's elset 07352.74304755. Below two pictures: the first showing it zipping through Cygnus (passing close to Deneb); the second showing it didappear behind the roof, with the Okean-O rk captured in the same image as a stray. Cassiopia is at top right.

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Lacrosse 5r, ISS, Iridium flares and comet 17P/Holmes

Yesterday was frosty and clear, albeit a bit moisty at the start of the night. A first quarter moon was low in the south.

I observed a nice pass of the International Space Station, two Iridium flares, and a pass of the Lacrosse 5 Rocket (05-016B).

(click images to enlarge)

Comet 17P/Holmes has grown large and very diffuse and was the target after midnight, when the sky had become less moist and the moon had set. It could still be seen naked eye, but with more difficulty than previously. It is about a degree wide. Below is a stack of 6 imges of 10 seconds each in wide-field; and a stack of 55 images of 5 seconds each at maximum zoom.

(click images to enlarge)

Comet 17P/Holmes, 3 December

Yesterday evening saw very dynamic weather, with the sky changing from open to overcast and back to open again in matters of minutes. During the short clear periods, the sky was however very transparent.

Comet 17P/Holmes was easy to see with the naked eye, as a large diffuse cloud somewhat to the right of alpha Persei.

Between 23h and 0h local time I managed to shoot 40 photographs of 5 second exposure duration each. The stacked result of these photographs is below (Canon Digital Ixus 400 compact camera on fixed tripod):

(click image to enlarge)

I revised my series of coma diameter measurements. I had been measuring astride the nucleus, but as the position of the nucleas grew more and more a-centric, that no longer resembled the largest coma diameter (perpendicular to the outflow axis, to avoid the tail). So I re-measured all images, this time determining he true maximum diameter.

Revised diagrams are below. 17P/Holmes is currently some 3.7 million km large.

(click images to enlarge)

Lacrosse 5 flaring, and another Iridium flare

A gale today had blown the skies clear by dusk. I observed Lacrosse 5 (05-016A) and saw it flare to mag. 0 at 16:49:08 +/- 5s UTC. I catched it on photograph with an exposure starting only some 2 seconds after the flare peak: but a strong gust of wind rocked the camera tripod during the exposure, leading to a disrupted trail image.

I was more lucky half an hour later, when Iridium 7 (97-020B) flared to mag. -2.5. It resulted in a nice picture:

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I combined this evenings Iridium 7 flare picture with that of the Iridium 97 flare yesterday. It nicely shows how the geometry of the orbit and fixed attitude for the Iridium constellation makes them flare at more or less the same location:

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Iridium 97 mag. -2 flare

Short clearings amidst flying clouds allowed me to image this mag. -2 flare of Iridium 97 (02-031A) flaring at 17:25:57 UTC. A few minutes earlier, Iridium 36 (97-056C) failed to deliver a predicted flare however.

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Comet 17P/Holmes getting larger and larger

Yesterday evening saw a period with clearings, which allowed me to photograph comet 17P/Holmes again. It is still visible by the naked eye, but less easy than 2 weeks ago (but still easier than M31). It is large now, going towards a degree (I measured a coma diameter of 50').

Below is a stack of 71 images of 5 seconds each with my Canon Digital Ixus 400 pocket camera on fixed tripod, and the lens on maximum zoom (3x).

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I again combined last evening's image with previous images, showing the growth of the comet in 3 weeks time:

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It was still clouded during the LEO satellite visibility window, alas.

Comet 17P/Holmes, 21.9 Nov 2007 (2)

In my previous post, I posted a 29 image stack of comet 17P/Holmes. I took 46 images that night but the software couldn't handle more than 29.

Using other software that can handle all 46 images, I get the result below, going deeper and showing the comet better:

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I used the earlier 29 image stack to make a comparison again with images obtained the previous two weeks. This again illustrates nicely the clear expansion of the comet during these two weeks:

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Comet 17P/Holmes, 21.9 Nov 2007

Yesterday evening it unexpectedly cleared. A bright waxing gibbous moon was in the sky, but nevertheless I managed to obtain a fine image of comet 17P/Holmes again. Visually, the comet was still visible by the naked eye, but less easy than previous due to the moonlight.

From the image obtained, I measured the coma to be 34.0' wide (that is more than an apparent moon diameter) at 2007 Nov 21.90. This corresponds to 2.4 million km in reality.

Below is the image obtained. It is a stack of 29 images of 5 seconds exposure each, taken with my Canon Digital Ixus 400 pocket camera at maximum zoom (3x) on a fixed tripod. Below the image are the updated size diagrams.

(click image to enlarge)

Satellites again: Lacrosse 5

Last evening finally allowed me to image a satellite pass again. Conditions were not perfect (hazy skies, later that evening it became completely overcast), but I could image a pass of the radar satellite Lacrosse 5 (05-016A).

At 17:35:20 UTC (Nov 18) it did it's infamous "disappearing trick" again, near the end of the 2nd exposure. In all, the two exposures yielded 3 points.

Comet 17P/Holmes over 2 million km large now

Another clear evening yesterday, so another photo-shoot on comet 17P/Holmes. It is still an easy naked-eye object even from the center of Leiden town, visible as a small cloud next to alpha Persei.

Compared to two nights ago the brighter inner part of the coma has now elongated and bifurcated. Below image is a stack of 29 images of 5 seconds each, taken from a fixed tripod with the Canon Digital Ixus 400 at maximum zoom (3x):

(click image to enlarge)

The bifurcation is more readily apparent in this false-colour version of the image:




A wide-field view ( a stack of 9 images of 10 seconds each) taken with the Ixus:

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Using ASTRORECORD I measured the coma size on the zoomed image to be 29.0' (Nov 17.97), corresponding to 2 million km in reality:

"Follow that comet!" (updated)

Yesterday (Nov 15-16) around local midnight it cleared again, and with comet 17P/Holmes in the zenith this meant some nice photographic results again.

The comet is still growing in size, the growth being virtually linear. Yesterday (Nov 15.98 UTC) it was 25.8' large, as measured with ASTRORECORD.

Size measurements like these can be used to calculate the true size of the cometary coma in kilometers (that's a fairly easy calculation actually, as the distance to the comet is known). This is the result:

University of Hawaii astronomers recently used a 3.6 meter telescope do determine a size of just over 1.4 million km on Nov 9th: as can be seen above, my simple Ixus camera does the job as well as the 3.6 meter telescope in getting a similar size result ( I marked the Nov 9 size as I find it in the diagram with red lines).

Below image is the image I took last night (stack of 25 images of 5 second exposure each with the Canon Ixus at 3x maximum zoom), with parts of earlier images taken Nov 7 and Nov 11 put in at the corrects scale, position and orientation.

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Below image shows a wide-field view. It is a stack of 7 images of 10 seconds each with the Ixus.

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Continued 17P/Holmes coverage

Short but bright clearings between hailshowers late last evening allowed me to image comet 17P/Holmes again. It still is a naked eye object, and still growing rapidly. It was notably larger yesterday than 4 days before.

Below is a stack of 16 images exposed 5 seconds each with the Canon Digital Ixus 400 on a fixed tripos and maximum optical zoom (3x):

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A false-colour version of this image draws attention to a slightly curved jet of gas flowing outwards (direction to the lower right in the image), and the egg-shaped coma (hint of a tail onset) that is the result:

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Below, I have combined last evening's image with that taken 4 days earlier, to show not only the movement but also the visibly growing coma diameter in these 4 days time:

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Next I used ASTRORECORD to measure the size of the coma on both images (these sizes were taken at an angle perpendicular to the sun-comet line). As the distance to the comet for these two dates is know, this allows a calculation of the actual size of the gas coma in km/miles. Last evening, this was 1.6 million km, or 1.0 million miles, growing at a rate of about 55 000 km/day or 2000 km/h:

date___________ _size____true size (km)__ _(miles)

2007 Nov 7.96___19.6’__ 1.380 million___0.862 million
2007 Nov 11.90__22.6’___1.599 million___0.999 million

How about the satellites?

SatTrackCam hasn't produced much satellite data during the past two months. The reasons for this include these:

1. A necessary focus on activities connected to a running research proposal, e.g. preparing for a selection committee hearing mid-October;

2. Generally bad weather conditions. Autumn and early winter are usually bad here, on the North Sea coast. The North Sea acts as a heat reservoir, generating clouds.

During this time of the year, the evening observing window for LEO satellites becomes shorter. Over the past weeks, when clearings developed they usually did so too late in the evening, after the end of the LEO satellite visibility window.

Movement and coma size increase of 17P/Holmes visualized

Below image is a combination of photographs I took on two different nights just over a week apart. It clearly demonstrates not only the movement of comet 17P/Holmes amongst the stars, but also the increase in the size of it's coma.

(click image to enlarge)

Yet more comet 17P/Holmes

Late last evening (around local midnight)it cleared again, and unlike two days earlier this time the sky quality was good. 17P/Holmes was an easy object for the naked eye, even from the center of Leiden.

So I repeated the experiment with 5 second exposures from a fixed tripod with my Canon Digital Ixus 400 compact camera at maximum zoom. The result is much better than the previous attempt a few days ago. This image, a stack of 16 photographs exposed 5 seconds each, highly satisfies me!

(click image to enlarge)

I also took a number of 10 second wide field images again. Below image shows (a part of) a stack of 8 wide field images, 10 second exposure each. The full constellation of Perseus is visible, with the comet as a bright yellowish object just above the alpha Persei association.

(click image to enlarge)

More comet 17P/Holmes

After a week of very bad weather, it cleared last evening. The skies were far from perfect (haze, and flying clouds), but I could snap a few pictures of comet 17P/Holmes again. The comet is a bit fainter now, and larger, but still naked eye.

I experimented with taking images with my Canon Digital Ixus pocket camera on maximum zoom on a fixed tripod. The maximum exposure to retain pinpoint stars turned out to be 5 seconds in this setting. I took a large number of such exposures, and then stacked 17 of them to simulate a 85 second exposure (1m 25s). The result was much better than I expected, and hence I am curious what the result would be whenever the sky would really be good:

(click image to enlarge)

Comet 17P/Holmes

After a long period of cloudy skies, it finally cleared last evening. Not in time to catch satellites, but in time to catch comet 17P/Holmes.

Comet 17P/Holmes dramatically brightened a week ago, from mag. +16 (!) to mag +2.5 (!!). That is spectacular and no other comet is known to do this this dramatically.

Yesterday the skies cleared only after the moon was already up. Nevertheless, and nothwithstanding my location in the middle of a town center, I could easily spot the comet with the naked eye as a bright "fuzzy" star just east of the alpha Persei group. In my 20 x 80 binoculars, it was a very bright nebulous globe. There is no sign of a tail, only a round coma some 20 arcminutes in size.

In wide field pictures, the object appears stellar due to this reason. Below image is a "stack" of three 10.7s images with my Canon Digital Ixus 400 pocket camera on a fixed tripod (so no guiding).

(click image to enlarge to full size)

Short session

Rainshowers dominate the weather since a few days. I did get a short period of clearings last night however, with very transparent sky. It enabled me to catch Lacrosse 5 (05-016A) on three images.

It did it's "disappearance trick" again at 22:30:31 UTC (Aug 19).