Friday, 30 November 2007

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).

(click image to enlarge)

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

(click image to enlarge)

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

Thursday, 22 November 2007

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:

(click image to enlarge)

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:

(click image to enlarge)

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)

Monday, 19 November 2007

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.

Sunday, 18 November 2007

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:

(click image to enlarge)

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:

Friday, 16 November 2007

"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.

(click image to enlarge)

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

(click image to enlarge)

Monday, 12 November 2007

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):

(click image to enlarge)

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:

(click image to enlarge)

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:

(click image to enlarge)

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

Saturday, 10 November 2007

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.

Friday, 9 November 2007

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)

Thursday, 8 November 2007

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)

Tuesday, 6 November 2007

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)