Tuesday 24 February 2009

Comet C/2007 N3 Lulin from Leiden

The weather is horrible these days, so I was much surprised by short clearings developing around local midnight last night. These allowed me a short peek and photo session on comet C/2007 N3 Lulin.

In the ETX-70 (small 7 cm refractor) at 14x, visually the comet was a nice fuzzy ball with a tail in NW-SE direction. Easy to find, especially as it was only a few degrees from Saturn.

I had only a short window of opportunity to photograph the comet before clouds came in again. Below image is a stack of 24 x 10 second exposures, made with the Canon EOS 450D (@800 ISO) and EF 50/2.5 Macro lesn (@ F2.8) between 23:18 and 23:26 UTC (23 feb).

Note that the conditions were far from perfect: not the best of skies, the comet low in the sky (35 degrees), and in the middle of Leiden town! So I am happy with the result.

(click image to enlarge)

Saturday 21 February 2009

Aftermath of a space collision

Over 200 fragments of the Feb 10th collision between Kosmos 2251 and Iridium 33 have now been catalogued. Together, they form two impressive orbital planes filled with debris. The amount of Kosmos 2251 debris catalogued so far is about twice as large as that for Iridium 33 - it seems the Kosmos took the most serious blow.

Most of this debris will stay up for tens of years. About 6% of the Kosmos and 3% of the Iridium debris will decay in the next 2.7 years.

(click images to enlarge)

Monday 16 February 2009

Feb 15 Texas-Nebraska daylight fireball was NOT satellite debris

Sightings of a bright daylight fireball seen from Texas to Nebraska on February 15th, have been widely reported in the press.

Contrary to what the FAA appears to be stating, this was definitely NOT debris from the collision between the Iridium 33 and Kosmos 2251 satellites on February 10th.

Video footage of the fireball (see below) shows that it moved clearly too fast for that, and was of too short duration, to be decaying satellite debris. In stead it is in line with a meteoritic fireball (asteroidal debris).

There is a clear difference in speed between the two categories: asteroidal/cometary debris moves at at least 11 km/s (and usually much faster) and typically lasts only a few seconds (as this fireball did). Satellite debris decaying moves at 7.5 to 8 km/s, so clearly slower, and typically has a much longer duration (due to the slower speed, but also because it enters at shallow angles). The video footage is incompatible with the appearance of decaying satellite debris. It is completely compatible with a meteoric fireball (asteroidal debris).

Thursday 12 February 2009

In Memoriam: Iridium 33

On 10 February 2009 at 16:56:00 UTC, Iridium 33 (97-051C) collided in orbit with the defunct Russian Kosmos 2251 satellite (93-036A). The collision occurred at 789 km altitude over the Siberian arctic, near 97.9 E, 72.5 N, with an orbital interception angle of 83.5 degrees. A cloud of rapidly spreading debris is now all that remains.

The collision occured at roughly the same altitude as the Chinese ASAT test on Fengyun 1C, and the resulting scenario for the debris cloud will be roughly similar to the latter event. An analysis of the Fengyun 1C debris field formation by Kelso can be read here.

On May 18th 2007, when Iridium 33 was still happy, alive and flaring, I shot the picture below:

(click image to enlarge)